74HCU04 LC Osc

Discussion in 'Electronic Design' started by Andrew Holme, Oct 8, 2006.

  1. Andrew Holme

    Andrew Holme Guest

    I built this 5 MHz oscillator using a Toko KANK4174 inductor, which is
    specified as having a Q of 100:



    74HCU04
    |\
    .------| >O-----o----
    | |/ |
    | .-.
    | | |
    | | | 3k3
    | 4.8uH '-'
    | ___ |
    o------UUU------o
    | |
    --- ---
    --- 390p --- 390p
    | |
    | |
    === ===
    GND GND
    (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

    Peak-to-peak voltage at the output is about 3V. Peak-to-peak voltage across
    either capacitor is about 0.5V

    The 3k3 forms a potential divider with the impedance across the capacitor:

    0.5 / 3 = Z / (3k3 + Z)
    Z = 660 ohms

    Dynamic impedance across the capacitively-tapped tuned circuit = Rp = 4*Z =
    2640 ohms

    Q = Rp/wL = 2640 / (2*pi*5e6*4.8e-6) = 17.5

    Why is my calculated Q so low?

    TIA
    Andrew
    Andrew Holme, Oct 8, 2006
    #1
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  2. Andrew Holme wrote:
    > I built this 5 MHz oscillator using a Toko KANK4174 inductor, which is
    > specified as having a Q of 100:
    >
    >
    >
    > 74HCU04
    > |\
    > .------| >O-----o----
    > | |/ |
    > | .-.
    > | | |
    > | | | 3k3
    > | 4.8uH '-'
    > | ___ |
    > o------UUU------o
    > | |
    > --- ---
    > --- 390p --- 390p
    > | |
    > | |
    > === ===
    > GND GND
    > (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
    >
    > Peak-to-peak voltage at the output is about 3V. Peak-to-peak voltage across
    > either capacitor is about 0.5V
    >
    > The 3k3 forms a potential divider with the impedance across the capacitor:
    >
    > 0.5 / 3 = Z / (3k3 + Z)
    > Z = 660 ohms


    Doesn't this formula assume that the 3 represents a zero
    impedance 3 volt source? I think you need to replace this
    voltage with the no load voltage from the inverter, and add
    the inverter's effective (Thevenin equivalent) output
    impedance to the 3k3 series resistor to approximate the
    effective resistance in series with the resonator.

    > Dynamic impedance across the capacitively-tapped tuned circuit = Rp = 4*Z =
    > 2640 ohms
    >
    > Q = Rp/wL = 2640 / (2*pi*5e6*4.8e-6) = 17.5
    >
    > Why is my calculated Q so low?
    >
    > TIA
    > Andrew
    >
    >
    John Popelish, Oct 8, 2006
    #2
    1. Advertising

  3. Andrew Holme

    Mike Monett Guest

    "Andrew Holme" <> wrote:

    > I built this 5 MHz oscillator using a Toko KANK4174 inductor, which is
    > specified as having a Q of 100:
    >
    >
    >
    > 74HCU04
    > |\
    > .------| >O-----o----
    > | |/ |
    > | .-.
    > | | |
    > | | | 3k3
    > | 4.8uH '-'
    > | ___ |
    > o------UUU------o
    > | |
    > --- ---
    > --- 390p --- 390p
    > | |
    > | |
    > === ===
    > GND GND
    > (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)


    The calculated resonant frequency is 5.202142 MHz, so XL = 156.8929 ohms.

    With an inductor Q of 100, you need to add a resistor in series or parallel
    with the inductor. The series value RS = 1.568929 ohms, and the parallel
    value RP = 15689.2908 ohms.

    > Peak-to-peak voltage at the output is about 3V. Peak-to-peak voltage
    > across either capacitor is about 0.5V


    The voltage across the capacitors is 3V p-p. The inductor provides a 180
    degree phase reversal, so the capacitor voltages are 180 degrees apart. The
    voltage across the inductor is 6V p-p.

    > The 3k3 forms a potential divider with the impedance across the
    > capacitor:
    >
    > 0.5 / 3 = Z / (3k3 + Z)
    > Z = 660 ohms


    The capacitive reactance XC = 78.446 ohms. I don't know where you got 660
    ohms, but it is incorrect.

    You are forgetting about resonance. Many people make this mistake. You
    cannot use the capacitive reactance as part of a voltage divider. You have
    to view the tank as part of a pi network. The inductor Q, plus the
    capacitor ratio, determines the input impedance.

    The inverter adds some delay, so the actual frequency of oscillation is
    slightly lower than the calculated tank resonance frequency. This changes
    the phase angle slightly, and makes the actual tank impedance very
    difficult to calculate. It is better to do this in SPICE and let it take
    care of these details.

    You can use the technique described in my article below on Crystal
    Oscillators to start the oscillator in steady-state. This speeds the
    analysis, and is still quite useful for tank Q's as low as 100.

    I use Microcap 8 since it has the peak search feature needed to locate the
    steady-state oscillation amplitude. PSpice may have a similar feature, but
    I have not figured how to do this in LTspice.

    > Dynamic impedance across the capacitively-tapped tuned circuit = Rp =
    > 4*Z = 2640 ohms
    >
    > Q = Rp/wL = 2640 / (2*pi*5e6*4.8e-6) = 17.5
    >
    > Why is my calculated Q so low?


    Using SPICE, the bandwidth at the -3dB points is 26.330 kHz. The center
    frequency is 5.20188 MHz, so the Q = 5.20188e6/(2*26.33e3) = 98.782

    This shows the 3.3K resistor has little effect on the loaded tank Q.

    > TIA
    > Andrew


    Regards,

    Mike Monett

    Antiviral, Antibacterial Silver Solution:
    http://silversol.freewebpage.org/index.htm
    SPICE Analysis of Crystal Oscillators:
    http://silversol.freewebpage.org/spice/xtal/clapp.htm
    Noise-Rejecting Wideband Sampler:
    http://www3.sympatico.ca/add.automation/sampler/intro.htm
    Mike Monett, Oct 8, 2006
    #3
  4. Andrew Holme

    Jim Thompson Guest

    On Sun, 08 Oct 2006 13:07:13 -0400, Mike Monett <> wrote:

    >"Andrew Holme" <> wrote:
    >
    >> I built this 5 MHz oscillator using a Toko KANK4174 inductor, which is
    >> specified as having a Q of 100:
    >>
    >>
    >>
    >> 74HCU04
    >> |\
    >> .------| >O-----o----
    >> | |/ |
    >> | .-.
    >> | | |
    >> | | | 3k3
    >> | 4.8uH '-'
    >> | ___ |
    >> o------UUU------o
    >> | |
    >> --- ---
    >> --- 390p --- 390p
    >> | |
    >> | |
    >> === ===
    >> GND GND
    >> (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

    >
    >The calculated resonant frequency is 5.202142 MHz, so XL = 156.8929 ohms.


    OK so far.

    >
    >With an inductor Q of 100, you need to add a resistor in series or parallel
    >with the inductor. The series value RS = 1.568929 ohms, and the parallel
    >value RP = 15689.2908 ohms.


    Neeerp! What's the Q before any added resistor?

    [snip]
    >
    >The inverter adds some delay, so the actual frequency of oscillation is
    >slightly lower than the calculated tank resonance frequency. This changes
    >the phase angle slightly, and makes the actual tank impedance very
    >difficult to calculate. It is better to do this in SPICE and let it take
    >care of these details.


    Not discernibly lower at 5MHz.

    [snip]

    ...Jim Thompson
    --
    | James E.Thompson, P.E. | mens |
    | Analog Innovations, Inc. | et |
    | Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
    | Phoenix, Arizona Voice:(480)460-2350 | |
    | E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
    | http://www.analog-innovations.com | 1962 |

    I love to cook with wine. Sometimes I even put it in the food.
    Jim Thompson, Oct 8, 2006
    #4
  5. Andrew Holme

    Ken Smith Guest

    In article <Xns985686A63AC4FNoemailadr@208.49.80.251>,
    Mike Monett <> wrote:
    >"Andrew Holme" <> wrote:
    >
    >> I built this 5 MHz oscillator using a Toko KANK4174 inductor, which is
    >> specified as having a Q of 100:
    >>
    >>
    >>
    >> 74HCU04
    >> |\
    >> .------| >O-----o----
    >> | |/ |
    >> | .-.
    >> | | |
    >> | | | 3k3
    >> | 4.8uH '-'
    >> | ___ |
    >> o------UUU------o
    >> | |
    >> --- ---
    >> --- 390p --- 390p
    >> | |
    >> | |
    >> === ===
    >> GND GND
    >> (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)

    [...]

    >You are forgetting about resonance. Many people make this mistake. You
    >cannot use the capacitive reactance as part of a voltage divider.


    Actually you can use capacitors and inductors and combinations there of as
    "voltage dividers". You just have to be prepared to have higher voltages
    coming out of the divider than went in etc because the impedances are not
    in phase. You have to include the "j"s in the math to get the right
    answers.

    --
    --
    forging knowledge
    Ken Smith, Oct 9, 2006
    #5
  6. Andrew Holme

    John - KD5YI Guest

    "Andrew Holme" <> wrote in message
    news:egb173$fkc$1$...
    >I built this 5 MHz oscillator using a Toko KANK4174 inductor, which is
    >specified as having a Q of 100:
    >
    >
    >
    > 74HCU04
    > |\
    > .------| >O-----o----
    > | |/ |
    > | .-.
    > | | |
    > | | | 3k3
    > | 4.8uH '-'
    > | ___ |
    > o------UUU------o
    > | |
    > --- ---
    > --- 390p --- 390p
    > | |
    > | |
    > === ===
    > GND GND
    > (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
    >
    > Peak-to-peak voltage at the output is about 3V. Peak-to-peak voltage
    > across either capacitor is about 0.5V
    >
    > The 3k3 forms a potential divider with the impedance across the capacitor:
    >
    > 0.5 / 3 = Z / (3k3 + Z)
    > Z = 660 ohms
    >
    > Dynamic impedance across the capacitively-tapped tuned circuit = Rp = 4*Z
    > = 2640 ohms
    >
    > Q = Rp/wL = 2640 / (2*pi*5e6*4.8e-6) = 17.5
    >
    > Why is my calculated Q so low?
    >
    > TIA
    > Andrew


    Hi, Andrew -

    Is the inductor's Q specified at 5 MHz? Be sure to account for the different
    intrinsic skin effect, if not.

    I have played with your circuit in LTSpice but I cannot reproduce your
    voltages. Inductor Q at 5 MHz may have something to do with it, but also
    Trise, Tfall, Tdelay of the inverter has a large effect. I used the Philips
    data sheet to specify those items and then adjusted them to get your values.
    I assumed Vcc of 3V since the inverter in LTSpice is a behavorial one and
    your output was 3V. What instrument did you use to measure the voltage? What
    was the probe impedance?

    If you want the LTSpice netlist, let me know. Good luck.

    John
    John - KD5YI, Oct 9, 2006
    #6
  7. Andrew Holme

    Jim Thompson Guest

    On Mon, 09 Oct 2006 01:05:07 GMT, "John - KD5YI"
    <> wrote:

    >
    >"Andrew Holme" <> wrote in message
    >news:egb173$fkc$1$...
    >>I built this 5 MHz oscillator using a Toko KANK4174 inductor, which is
    >>specified as having a Q of 100:
    >>
    >>
    >>
    >> 74HCU04
    >> |\
    >> .------| >O-----o----
    >> | |/ |
    >> | .-.
    >> | | |
    >> | | | 3k3
    >> | 4.8uH '-'
    >> | ___ |
    >> o------UUU------o
    >> | |
    >> --- ---
    >> --- 390p --- 390p
    >> | |
    >> | |
    >> === ===
    >> GND GND
    >> (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
    >>
    >> Peak-to-peak voltage at the output is about 3V. Peak-to-peak voltage
    >> across either capacitor is about 0.5V
    >>
    >> The 3k3 forms a potential divider with the impedance across the capacitor:
    >>
    >> 0.5 / 3 = Z / (3k3 + Z)
    >> Z = 660 ohms
    >>
    >> Dynamic impedance across the capacitively-tapped tuned circuit = Rp = 4*Z
    >> = 2640 ohms
    >>
    >> Q = Rp/wL = 2640 / (2*pi*5e6*4.8e-6) = 17.5
    >>
    >> Why is my calculated Q so low?
    >>
    >> TIA
    >> Andrew

    >
    >Hi, Andrew -
    >
    >Is the inductor's Q specified at 5 MHz? Be sure to account for the different
    >intrinsic skin effect, if not.
    >
    >I have played with your circuit in LTSpice but I cannot reproduce your
    >voltages. Inductor Q at 5 MHz may have something to do with it, but also
    >Trise, Tfall, Tdelay of the inverter has a large effect. I used the Philips
    >data sheet to specify those items and then adjusted them to get your values.
    >I assumed Vcc of 3V since the inverter in LTSpice is a behavorial one and
    >your output was 3V. What instrument did you use to measure the voltage? What
    >was the probe impedance?
    >
    >If you want the LTSpice netlist, let me know. Good luck.
    >
    >John
    >


    In PSpice, assuming QL=100, the effective Q is ~45.

    A real 74HCU04 (I have the device-level models) is quite good, and has
    a barely noticeable effect at 5.2MHz.

    ...Jim Thompson
    --
    | James E.Thompson, P.E. | mens |
    | Analog Innovations, Inc. | et |
    | Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
    | Phoenix, Arizona Voice:(480)460-2350 | |
    | E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
    | http://www.analog-innovations.com | 1962 |

    I love to cook with wine. Sometimes I even put it in the food.
    Jim Thompson, Oct 9, 2006
    #7
  8. Andrew Holme

    Mark Guest

    John - KD5YI wrote:
    > "Andrew Holme" <> wrote in message
    > news:egb173$fkc$1$...
    > >I built this 5 MHz oscillator using a Toko KANK4174 inductor, which is
    > >specified as having a Q of 100:
    > >

    snip
    > >
    > > Why is my calculated Q so low?
    > >

    >

    100 is the UNLOADED Q of the inductor.

    In the circuit the Q is the LOADED Q.

    Mark
    Mark, Oct 9, 2006
    #8
  9. Andrew Holme

    Mike Monett Guest

    "John - KD5YI" <> wrote:

    > Hi, Andrew -


    > Is the inductor's Q specified at 5 MHz? Be sure to account for the
    > different intrinsic skin effect, if not.


    > I have played with your circuit in LTSpice but I cannot reproduce your
    > voltages. Inductor Q at 5 MHz may have something to do with it, but
    > also Trise, Tfall, Tdelay of the inverter has a large effect. I used
    > the Philips data sheet to specify those items and then adjusted them
    > to get your values. I assumed Vcc of 3V since the inverter in LTSpice
    > is a behavorial one and your output was 3V. What instrument did you
    > use to measure the voltage? What was the probe impedance?


    > If you want the LTSpice netlist, let me know. Good luck.


    > John


    John,

    I tried to find the inductor on the toyo site but it was not listed.

    Usually the Q for that value is measured at 7.9MHz. This is no too far from
    5.2MHz, so it should be fairly close. But I find a Q of 100 a bit high.
    Usually it's around 30 to 50.

    I did my analysis at 5V, so it will be a bit different from yours. Could
    you post your ASC file so we can compare the results from MicroCap 8?

    Regards,

    Mike Monett

    Antiviral, Antibacterial Silver Solution:
    http://silversol.freewebpage.org/index.htm
    SPICE Analysis of Crystal Oscillators:
    http://silversol.freewebpage.org/spice/xtal/clapp.htm
    Noise-Rejecting Wideband Sampler:
    http://www3.sympatico.ca/add.automation/sampler/intro.htm
    Mike Monett, Oct 9, 2006
    #9
  10. Andrew Holme

    Didi Guest

    This triggered a 15+ year old memory... Back then I needed a 110-120
    MHz
    clock generator (TTL levels); I did it using a 74AS00 (or was it
    04?...), an inductor
    I had routed on the PCB, a crystal - I had to locate something suitable
    to work
    between 115 and 120 MHz at 5-th, and a tiny trimcap... Obviously each
    unit
    had to be trimmed so the LC frequency would match the crystal, the
    "lock"
    was easily identifiable on a scope. The footprint was that of a typical
    metal
    crystal oscillator (DIP-14 corner pins only style), the height somehat
    more.
    It worked and managed to stay "locked" to the crystal over a pretty
    wide
    temperature range (that AS or F chip was quite an oven, especially
    at about 120 MHz... :).
    Just a related memory, hopefully on something mad enough to be worth
    remembering :).

    Dimiter

    ------------------------------------------------------
    Dimiter Popoff Transgalactic Instruments

    http://www.tgi-sci.com
    ------------------------------------------------------

    Jim Thompson wrote:
    > On Mon, 09 Oct 2006 01:05:07 GMT, "John - KD5YI"
    > <> wrote:
    >
    > >
    > >"Andrew Holme" <> wrote in message
    > >news:egb173$fkc$1$...
    > >>I built this 5 MHz oscillator using a Toko KANK4174 inductor, which is
    > >>specified as having a Q of 100:
    > >>
    > >>
    > >>
    > >> 74HCU04
    > >> |\
    > >> .------| >O-----o----
    > >> | |/ |
    > >> | .-.
    > >> | | |
    > >> | | | 3k3
    > >> | 4.8uH '-'
    > >> | ___ |
    > >> o------UUU------o
    > >> | |
    > >> --- ---
    > >> --- 390p --- 390p
    > >> | |
    > >> | |
    > >> === ===
    > >> GND GND
    > >> (created by AACircuit v1.28.6 beta 04/19/05 www.tech-chat.de)
    > >>
    > >> Peak-to-peak voltage at the output is about 3V. Peak-to-peak voltage
    > >> across either capacitor is about 0.5V
    > >>
    > >> The 3k3 forms a potential divider with the impedance across the capacitor:
    > >>
    > >> 0.5 / 3 = Z / (3k3 + Z)
    > >> Z = 660 ohms
    > >>
    > >> Dynamic impedance across the capacitively-tapped tuned circuit = Rp = 4*Z
    > >> = 2640 ohms
    > >>
    > >> Q = Rp/wL = 2640 / (2*pi*5e6*4.8e-6) = 17.5
    > >>
    > >> Why is my calculated Q so low?
    > >>
    > >> TIA
    > >> Andrew

    > >
    > >Hi, Andrew -
    > >
    > >Is the inductor's Q specified at 5 MHz? Be sure to account for the different
    > >intrinsic skin effect, if not.
    > >
    > >I have played with your circuit in LTSpice but I cannot reproduce your
    > >voltages. Inductor Q at 5 MHz may have something to do with it, but also
    > >Trise, Tfall, Tdelay of the inverter has a large effect. I used the Philips
    > >data sheet to specify those items and then adjusted them to get your values.
    > >I assumed Vcc of 3V since the inverter in LTSpice is a behavorial one and
    > >your output was 3V. What instrument did you use to measure the voltage? What
    > >was the probe impedance?
    > >
    > >If you want the LTSpice netlist, let me know. Good luck.
    > >
    > >John
    > >

    >
    > In PSpice, assuming QL=100, the effective Q is ~45.
    >
    > A real 74HCU04 (I have the device-level models) is quite good, and has
    > a barely noticeable effect at 5.2MHz.
    >
    > ...Jim Thompson
    > --
    > | James E.Thompson, P.E. | mens |
    > | Analog Innovations, Inc. | et |
    > | Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
    > | Phoenix, Arizona Voice:(480)460-2350 | |
    > | E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
    > | http://www.analog-innovations.com | 1962 |
    >
    > I love to cook with wine. Sometimes I even put it in the food.
    Didi, Oct 9, 2006
    #10
  11. Andrew Holme

    John - KD5YI Guest

    "Mike Monett" <> wrote in message
    news:Xns9856DB270D30ANoemailadr@208.49.80.251...
    > "John - KD5YI" <> wrote:
    >
    >> Hi, Andrew -

    >
    >> Is the inductor's Q specified at 5 MHz? Be sure to account for the
    >> different intrinsic skin effect, if not.

    >
    >> I have played with your circuit in LTSpice but I cannot reproduce your
    >> voltages. Inductor Q at 5 MHz may have something to do with it, but
    >> also Trise, Tfall, Tdelay of the inverter has a large effect. I used
    >> the Philips data sheet to specify those items and then adjusted them
    >> to get your values. I assumed Vcc of 3V since the inverter in LTSpice
    >> is a behavorial one and your output was 3V. What instrument did you
    >> use to measure the voltage? What was the probe impedance?

    >
    >> If you want the LTSpice netlist, let me know. Good luck.

    >
    >> John

    >
    > John,
    >
    > I tried to find the inductor on the toyo site but it was not listed.


    Yes, I tried to find it as well. No luck.

    > Usually the Q for that value is measured at 7.9MHz. This is no too far
    > from
    > 5.2MHz, so it should be fairly close. But I find a Q of 100 a bit high.
    > Usually it's around 30 to 50.



    I agree that the Q seems to be specified unusually high.


    > I did my analysis at 5V, so it will be a bit different from yours. Could
    > you post your ASC file so we can compare the results from MicroCap 8?


    Yes, of course. See below.

    > Regards,
    >
    > Mike Monett


    I also added some series resistance to each capacitor to make their Q about
    1000. The inductor is specified to be 1.5 ohms.

    The Trise (equals Tfall) is a bit longer thant the Philips data sheet says.
    Also, the Tdelay is longer. I don't remember any more gotchas at this time.
    If you have questions, please ask. My email is groups5 at verizon dot com.

    I have been interested in the difficulties of measuring Q for some time now.
    I will be following this thread as closely as my situation permits.

    John

    ***********************************************

    Version 4
    SHEET 1 880 680
    WIRE 96 128 -96 128
    WIRE 208 128 160 128
    WIRE 96 160 96 144
    WIRE 208 160 208 128
    WIRE -96 272 -96 128
    WIRE 0 272 -96 272
    WIRE 128 272 80 272
    WIRE 208 272 208 240
    WIRE 208 272 128 272
    WIRE -96 288 -96 272
    WIRE 128 288 128 272
    WIRE -96 368 -96 352
    WIRE 128 368 128 352
    FLAG 96 160 0
    FLAG 128 368 0
    FLAG -96 368 0
    SYMBOL Digital\\inv 96 64 R0
    WINDOW 3 -199 2 Left 0
    SYMATTR InstName A1
    SYMATTR Value Trise=20n Td=30n Vhigh=3
    SYMBOL res 192 144 R0
    SYMATTR InstName R1
    SYMATTR Value 3k3
    SYMBOL cap 112 288 R0
    SYMATTR InstName C1
    SYMATTR Value 390p
    SYMATTR SpiceLine Rser=.08
    SYMBOL ind 96 256 R90
    WINDOW 0 5 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName L1
    SYMATTR Value 4µ8
    SYMATTR SpiceLine Rser=1.5
    SYMBOL cap -112 288 R0
    SYMATTR InstName C2
    SYMATTR Value 390p
    SYMATTR SpiceLine Rser=.08
    TEXT -316 160 Left 0 !.tran 0 20u 0 1n
    John - KD5YI, Oct 9, 2006
    #11
  12. Andrew Holme

    Mike Monett Guest

    "John - KD5YI" <> wrote:

    >> Could you post your ASC file so we can compare the results from
    >> MicroCap 8?


    > Yes, of course. See below.


    OK, Thanks. I'll take a look and see what the differences are.

    > I also added some series resistance to each capacitor to make
    > their Q about 1000.


    That's probably realistic Q at 5MHz, but the inductor Q will
    dominate.

    > The inductor is specified to be 1.5 ohms.


    That's probably the max DC resistance. That won't have much effect in
    this circuit where the input bias is probably in the attoamp region:)

    I redid the analysis using a Q of 30 and VCC of 3V.

    The inductor series resistance went to 5.229 ohms, and the cap
    voltage dropped to 585.192 mV which is close to Andrew's value. So I
    think the problem is an inductor Q of 100 was way too high.

    The AC analysis showed the center frequency dropped slightly from
    5.202142MHz to 5.199250 MHz. I'm using NMOS and PMOS devices to
    model the 74U04, so probably the prop delay increased slightly. The
    rise and fall time doesn't seem to have much effect since the
    inverter output is aligned with the sinusoidal waveform across the
    tank input cap.

    The bandwidth at the -3.015dB points is 174.5454 KHz, so the loaded
    Q is 5.199250e6 / 174.5454e3 = 29.787, which is very close to the
    original Q of 30. This shows as the inductor Q decreases, the 3.3k
    resistor has even less effect on bandwidth. Which is what you expect.

    > The Trise (equals Tfall) is a bit longer than the Philips data
    > sheet says. Also, the Tdelay is longer. I don't remember any more
    > gotchas at this time. If you have questions, please ask. My email
    > is groups5 at verizon dot com.


    Thanks, I'll look at the LTspice version and see how it compares to
    MicroCap 8.

    > I have been interested in the difficulties of measuring Q for some
    > time now. I will be following this thread as closely as my
    > situation permits.


    > John


    Thanks, John. Don't work too hard:)

    Regards,

    Mike Monett

    Antiviral, Antibacterial Silver Solution:
    http://silversol.freewebpage.org/index.htm
    SPICE Analysis of Crystal Oscillators:
    http://silversol.freewebpage.org/spice/xtal/clapp.htm
    Noise-Rejecting Wideband Sampler:
    http://www3.sympatico.ca/add.automation/sampler/intro.htm
    Mike Monett, Oct 9, 2006
    #12
  13. Andrew Holme

    Mike Monett Guest

    Mike Monett <> wrote:

    > The bandwidth at the -3.015dB points is 174.5454 KHz, so the
    > loaded Q is 5.199250e6 / 174.5454e3 = 29.787, which is very close
    > to the original Q of 30. This shows as the inductor Q decreases,
    > the 3.3k resistor has even less effect on bandwidth. Which is what
    > you expect.


    Something didn't seem right with these high Q values, so I went back
    and checked. It turns out I was measuring the bandwidth wrong. To do
    the AC analysis, I simply broke the loop and injected the AC source
    to the input of the inverter. However, the output of the inverter
    changes with load when operating in the linear region, so the
    apparent Q was too high.

    Since the output is normally close to saturation when the oscillator
    is running at normal amplitude, we can consider the top of the 3.3k
    resistor is effectively at RF ground.

    Eliminating the inverter and connecting the AC source to the top of
    the 3.3k resistor gives a bandwidth of 236.158 KHz, and a resulting
    Q of 5.197476e6 / 236.158e3 = 22.0084.

    So the 3.3k has more effect on the tank Q than previous calculations
    showed. This makes sense.

    Regards,

    Mike Monett

    Antiviral, Antibacterial Silver Solution:
    http://silversol.freewebpage.org/index.htm
    SPICE Analysis of Crystal Oscillators:
    http://silversol.freewebpage.org/spice/xtal/clapp.htm
    Noise-Rejecting Wideband Sampler:
    http://www3.sympatico.ca/add.automation/sampler/intro.htm
    Mike Monett, Oct 9, 2006
    #13
  14. Andrew Holme

    Andrew Holme Guest

    John - KD5YI wrote:
    [snip]
    > Hi, Andrew -
    >
    > Is the inductor's Q specified at 5 MHz? Be sure to account for the different
    > intrinsic skin effect, if not.
    >
    > I have played with your circuit in LTSpice but I cannot reproduce your
    > voltages. Inductor Q at 5 MHz may have something to do with it, but also
    > Trise, Tfall, Tdelay of the inverter has a large effect. I used the Philips
    > data sheet to specify those items and then adjusted them to get your values.
    > I assumed Vcc of 3V since the inverter in LTSpice is a behavorial one and
    > your output was 3V. What instrument did you use to measure the voltage? What
    > was the probe impedance?
    >
    > If you want the LTSpice netlist, let me know. Good luck.
    >
    > John


    Hi John,

    Vdd is 5V. The voltages were measured with 1Mohm x10 'scope probes.

    The coil is from the old 10K series, and Q is 100 according to my old
    Cirkit catalogue.

    I reproduced the voltages in LTSpice (see below). I think my original
    (back of envelope) maths was wrong; and my circuit is functioning
    correctly.

    Thanks,
    Andrew.



    Version 4
    SHEET 1 880 680
    WIRE -112 144 -336 144
    WIRE 16 144 -32 144
    WIRE 96 144 16 144
    WIRE 208 144 176 144
    WIRE 320 144 288 144
    WIRE -336 192 -336 144
    WIRE 16 208 16 144
    WIRE 320 208 320 144
    WIRE -336 320 -336 272
    WIRE 16 320 16 272
    WIRE 320 320 320 272
    FLAG -336 320 0
    FLAG 16 320 0
    FLAG 320 320 0
    SYMBOL cap 304 208 R0
    SYMATTR InstName C1
    SYMATTR Value 390p
    SYMBOL cap 0 208 R0
    SYMATTR InstName C2
    SYMATTR Value 390p
    SYMBOL ind 80 160 R270
    WINDOW 0 32 56 VTop 0
    WINDOW 3 5 56 VBottom 0
    SYMATTR InstName L1
    SYMATTR Value 4.8µH
    SYMBOL res 304 128 R90
    WINDOW 0 0 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName R1
    SYMATTR Value 1.5
    SYMBOL res -16 128 R90
    WINDOW 0 0 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName R2
    SYMATTR Value 3k3
    SYMBOL voltage -336 176 R0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V1
    SYMATTR Value SINE(0 1.5 5000000)
    TEXT -370 506 Left 0 !.tran 20us
    Andrew Holme, Oct 9, 2006
    #14
  15. Andrew Holme

    Andrew Holme Guest

    Andrew Holme wrote:
    > John - KD5YI wrote:
    > [snip]
    > > Hi, Andrew -
    > >
    > > Is the inductor's Q specified at 5 MHz? Be sure to account for the different
    > > intrinsic skin effect, if not.
    > >
    > > I have played with your circuit in LTSpice but I cannot reproduce your
    > > voltages. Inductor Q at 5 MHz may have something to do with it, but also
    > > Trise, Tfall, Tdelay of the inverter has a large effect. I used the Philips
    > > data sheet to specify those items and then adjusted them to get your values.
    > > I assumed Vcc of 3V since the inverter in LTSpice is a behavorial one and
    > > your output was 3V. What instrument did you use to measure the voltage? What
    > > was the probe impedance?
    > >
    > > If you want the LTSpice netlist, let me know. Good luck.
    > >
    > > John

    >
    > Hi John,
    >
    > Vdd is 5V. The voltages were measured with 1Mohm x10 'scope probes.
    >
    > The coil is from the old 10K series, and Q is 100 according to my old
    > Cirkit catalogue.
    >
    > I reproduced the voltages in LTSpice (see below). I think my original
    > (back of envelope) maths was wrong; and my circuit is functioning
    > correctly.
    >
    > Thanks,
    > Andrew.


    [snip]

    I've done some more simulation in LTSpice and plotted the Bode response
    of the LC network, and I now lean back towards thinking that my
    original math *was* correct, and something is wrong with my circuit.
    The key thing is that the voltages at either end of the 3k3 resistor
    are in phase. The only way I can get this in simulation is by placing
    a large value resistor in series with the inductor. Could the Toko
    coil be saturating?
    Andrew Holme, Oct 9, 2006
    #15
  16. Andrew Holme

    Mike Monett Guest

    "Andrew Holme" <> wrote:

    >> Vdd is 5V. The voltages were measured with 1Mohm x10 'scope probes.
    >>
    >> The coil is from the old 10K series, and Q is 100 according to my old
    >> Cirkit catalogue.
    >>
    >> I reproduced the voltages in LTSpice (see below). I think my
    >> original (back of envelope) maths was wrong; and my circuit is
    >> functioning correctly.
    >>
    >> Thanks,
    >> Andrew.

    >
    > [snip]
    >
    > I've done some more simulation in LTSpice and plotted the Bode
    > response of the LC network, and I now lean back towards thinking that
    > my original math *was* correct, and something is wrong with my
    > circuit. The key thing is that the voltages at either end of the 3k3
    > resistor are in phase. The only way I can get this in simulation is
    > by placing a large value resistor in series with the inductor. Could
    > the Toko coil be saturating?


    Hi Andrew,

    It's unlikely the inductor is saturating. However, there are a number of
    other problems that should be addressed. Here are some of them:

    1. It is unlikely the inductor is 4.8uH. The nearest standard value is
    4.7uH. This means the center frequency should be 5.257 MHz, not 5.00 MHz as
    your LTspice file assumes.

    2. A Q of 100 is certainly possible at these frequencies, but probably not
    in a standard commercial inductor. The expected Q is probably between 30
    and 50. You should be able to measure the actual Q and inductance of your
    coil with a simple sig generator, inexpensive frequency counter, and scope.

    3. The 1.5 ohm resistor in your LTspice file is probably the maximum dc
    resistance. This gives a much larger Q than expected for standard
    inductors. You can easily calculate the proper value to use in your LTspice
    analysis using more realistic Q values.

    4. Your LTspice file drives the tank with a 5.00 MHz sine wave. This is
    below the resonant frequency of the tank, so the resulting signal
    amplitude you measure in SPICE has little relation to your actual circuit.

    5. If you did a Bode plot, you should have noticed the resonant frequency
    was well above 5.00 MHz. This should have alerted you that something was
    wrong with your analysis.

    And so on...

    With the large number of basic issues shown above, there are probably even
    more involved with your bench measurements. These would likely take a long
    time to resolve.

    Regards,

    Mike Monett

    Antiviral, Antibacterial Silver Solution:
    http://silversol.freewebpage.org/index.htm
    SPICE Analysis of Crystal Oscillators:
    http://silversol.freewebpage.org/spice/xtal/clapp.htm
    Noise-Rejecting Wideband Sampler:
    http://www3.sympatico.ca/add.automation/sampler/intro.htm
    Mike Monett, Oct 9, 2006
    #16
  17. Andrew Holme

    Joop Guest

    On 9 Oct 2006 05:10:43 -0700, "Andrew Holme" <>
    wrote:

    >
    >Andrew Holme wrote:
    >> John - KD5YI wrote:
    >> [snip]
    >> > Hi, Andrew -
    >> >
    >> > Is the inductor's Q specified at 5 MHz? Be sure to account for the different
    >> > intrinsic skin effect, if not.
    >> >
    >> > I have played with your circuit in LTSpice but I cannot reproduce your
    >> > voltages. Inductor Q at 5 MHz may have something to do with it, but also
    >> > Trise, Tfall, Tdelay of the inverter has a large effect. I used the Philips
    >> > data sheet to specify those items and then adjusted them to get your values.
    >> > I assumed Vcc of 3V since the inverter in LTSpice is a behavorial one and
    >> > your output was 3V. What instrument did you use to measure the voltage? What
    >> > was the probe impedance?
    >> >
    >> > If you want the LTSpice netlist, let me know. Good luck.
    >> >
    >> > John

    >>
    >> Hi John,
    >>
    >> Vdd is 5V. The voltages were measured with 1Mohm x10 'scope probes.
    >>
    >> The coil is from the old 10K series, and Q is 100 according to my old
    >> Cirkit catalogue.
    >>
    >> I reproduced the voltages in LTSpice (see below). I think my original
    >> (back of envelope) maths was wrong; and my circuit is functioning
    >> correctly.
    >>
    >> Thanks,
    >> Andrew.

    >
    >[snip]
    >
    >I've done some more simulation in LTSpice and plotted the Bode response
    >of the LC network, and I now lean back towards thinking that my
    >original math *was* correct, and something is wrong with my circuit.
    >The key thing is that the voltages at either end of the 3k3 resistor
    >are in phase. The only way I can get this in simulation is by placing
    >a large value resistor in series with the inductor. Could the Toko
    >coil be saturating?

    Your math was probably correct.

    I used Netcalc to translate the components to parallel form. This
    gives (with RL=1.52 ohm and 74HCU04 Rout=0):

    4.8uH // 195pF // 13200 ohm

    Q=Rp*w*C => 16.8

    Which is pretty close to yours.

    Cheers,

    Joop
    Joop, Oct 9, 2006
    #17
  18. Andrew Holme

    Joop Guest

    >>I've done some more simulation in LTSpice and plotted the Bode response
    >>of the LC network, and I now lean back towards thinking that my
    >>original math *was* correct, and something is wrong with my circuit.
    >>The key thing is that the voltages at either end of the 3k3 resistor
    >>are in phase. The only way I can get this in simulation is by placing
    >>a large value resistor in series with the inductor. Could the Toko
    >>coil be saturating?

    >Your math was probably correct.
    >
    >I used Netcalc to translate the components to parallel form. This
    >gives (with RL=1.52 ohm and 74HCU04 Rout=0):
    >
    >4.8uH // 195pF // 13200 ohm
    >
    >Q=Rp*w*C => 16.8
    >
    >Which is pretty close to yours.
    >
    >Cheers,
    >
    >Joop

    Sorry I made some wrong calculations there.
    It should have been:

    4.8uH // 195pF // 7277 ohm

    And Q = 7277*2*pi*195pico = 46.3

    After the messy calculations I though I'd better check it in LT-spice.
    The -3dBV bandwidth = 112K

    Which gives Q = f/delta-f = 5200/112 = 46.4
    That should be better.
    Joop, Oct 9, 2006
    #18
  19. In article <>,
    Andrew Holme <> wrote:

    > I've done some more simulation in LTSpice and plotted the Bode
    > response of the LC network, and I now lean back towards thinking
    > that my original math *was* correct, and something is wrong with
    > my circuit. The key thing is that the voltages at either end of
    > the 3k3 resistor are in phase. The only way I can get this in
    > simulation is by placing a large value resistor in series with
    > the inductor. Could the Toko coil be saturating?



    V1 V2
    3k3 | R L |
    ---/\/\----(1)---+---/\/\---))))---+
    | |
    Z12--> C1=== ===C2
    | |
    -----------(2)---+-----------------+--0v

    If I've done the algebra right, Z12 is not resistive
    if calculated at w.L = 1/(w.C1) + 1/(w.C2), which
    is the resonant frequency of the pi-network.

    Z12 = 1/R*(w.C1)^2 - j/(w.C1).

    That looks like a resistor in series with a capacitor.
    If the Q is high then R is low and the resistive part
    is very high compared to the capacitive part.

    To get your 0.5V for V1 and V2 then R is about 9.4 ohms.

    --
    Tony Williams.
    Tony Williams, Oct 11, 2006
    #19
  20. Andrew Holme

    Mike Monett Guest

    Tony Williams <> wrote:

    >
    > V1 V2
    > 3k3 | R L |
    > ---/\/\----(1)---+---/\/\---))))---+
    > | |
    > Z12--> C1=== ===C2
    > | |
    > -----------(2)---+-----------------+--0v
    >
    > If I've done the algebra right, Z12 is not resistive
    > if calculated at w.L = 1/(w.C1) + 1/(w.C2), which
    > is the resonant frequency of the pi-network.
    >
    > Z12 = 1/R*(w.C1)^2 - j/(w.C1).
    >
    > That looks like a resistor in series with a capacitor.
    > If the Q is high then R is low and the resistive part
    > is very high compared to the capacitive part.
    >
    > To get your 0.5V for V1 and V2 then R is about 9.4 ohms.


    Hi Tony,

    A series resistance of 9.4 ohms would produce an inductor Q of 15.7. This
    is lower than typical commercial inductors, which may have typical Q's of
    30 to 50. This indicates there may be some error in the measurement. For
    example, the nearest standard inductor is 4.7uH, so the tank resonance will
    occur at 5.257MHz, not at 5.00MHz as Andrew assumes.

    Below is an LTspice ASC file of a pi network at 5.00 MHz using a 4.7uH
    inductor and a typical Q of 30. The second file is the plt file with the
    phase of the current through the 3.3k resistor shown on a separate graph.

    As shown in the AC analysis, the phase angle of the current through the
    resistor around resonance is very close to zero degrees. This indicates the
    input impedance of the tank near resonance is resistive, and not capacitive
    as many people seem to think.

    The reason is the inductor provides a 180 degree phase reversal, so the
    capacitive currents cancel at the input to the pi network. This places the
    resistive portion of the tank impedance in series with the 3.3k input
    resistor.

    Since the phase angle changes rapidly around resonance, an attempt to
    calculate the input impedance quickly runs into trouble as you don't know
    the exact frequency the circuit will oscillate at. This means SPICE is the
    best and easiest way to analyze these circuits.

    Here's the ASC file:

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Version 4
    SHEET 1 880 680
    WIRE -192 144 -256 144
    WIRE -112 144 -192 144
    WIRE 16 144 -32 144
    WIRE 96 144 16 144
    WIRE 208 144 176 144
    WIRE 320 144 288 144
    WIRE -256 192 -256 144
    WIRE 16 208 16 144
    WIRE 320 208 320 144
    WIRE -256 320 -256 272
    WIRE 16 320 16 272
    WIRE 320 320 320 272
    FLAG -256 320 0
    FLAG 16 320 0
    FLAG 320 320 0
    FLAG -192 144 Vin
    FLAG 320 144 Vout
    FLAG 16 144 VCap
    SYMBOL cap 304 208 R0
    SYMATTR InstName C1
    SYMATTR Value 431.1pf
    SYMBOL cap 0 208 R0
    SYMATTR InstName C2
    SYMATTR Value 431.1pf
    SYMBOL ind 80 160 R270
    WINDOW 0 32 56 VTop 0
    WINDOW 3 5 56 VBottom 0
    SYMATTR InstName L1
    SYMATTR Value 4.7µh
    SYMBOL res 304 128 R90
    WINDOW 0 0 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName R2
    SYMATTR Value 4.92
    SYMBOL res -128 128 M90
    WINDOW 0 0 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    SYMATTR InstName R1
    SYMATTR Value 3k3
    SYMBOL voltage -256 176 R0
    WINDOW 123 24 134 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR Value2 AC 1
    SYMATTR InstName V1
    SYMATTR Value SINE(0 1.5 5000000)
    TEXT -80 72 Left 0 ;'5.0 MHz pi Network
    TEXT -216 360 Left 0 !.ac lin 10k 4.8e6 5.2e6

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    Here's the PLT file

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    [AC Analysis]
    {
    Npanes: 2
    {
    traces: 1 {34603011,0,"I(R1)"}
    X: ('M',2,4.8e+006,40000,5.2e+006)
    Y[0]: (' ',1,0.000223872113856834,0.2,0.000288403150312661)
    Y[1]: (' ',0,-8,2,10)
    Log: 0 2 0
    GridStyle: 1
    PltPhi: 1
    },
    {
    traces: 2 {524290,0,"V(vout)"} {524293,0,"V(vcap)"}
    X: ('M',2,4.8e+006,40000,5.2e+006)
    Y[0]: (' ',1,0.10471285480509,0.7,0.25409727055493)
    Y[1]: (' ',0,-240,30,60)
    Log: 0 2 0
    GridStyle: 1
    PltMag: 1
    }
    }

    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


    Regards,

    Mike Monett

    Antiviral, Antibacterial Silver Solution:
    http://silversol.freewebpage.org/index.htm
    SPICE Analysis of Crystal Oscillators:
    http://silversol.freewebpage.org/spice/xtal/clapp.htm
    Noise-Rejecting Wideband Sampler:
    http://www3.sympatico.ca/add.automation/sampler/intro.htm
    Mike Monett, Oct 11, 2006
    #20
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