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Newbie - Trying to simulae 3.5MHz Xmtr - LTSpice

Discussion in 'Electronic Design' started by Talion, Dec 23, 2004.

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  1. Talion

    Talion Guest

    Greetings,

    I have never used a schematic capture program before and I am just getting back
    into electronics after many years, so I'm a bit rusty. Please bear with me.

    I am trying to simulate a low-power transmitter in the 3.5 MHz range in LTSpice.
    I would like to look at a plot of the emissions at ANT to see what my frequency
    output looks Like. Effectively, a frequency spectrum plot. I understand I should
    use an FFT plot after running a transient simulation, but I seem to be having no
    luck.

    I'm at a loss as to whether my schematic is faulty, I don't understand how to
    properly use LTSpice or both. In particular, I wonder if I have configured the
    crystal properly (a colorburst crystal) and whether I need a 50 Ohm load instead
    of the ANT output?

    Any insight would be appreciated, and I thank you in advance.

    My LTSpice circuit follows:

    ----- snip 3.5MHZ xmtr.asc -----

    Version 4
    SHEET 1 892 680
    WIRE 96 144 48 144
    WIRE -16 144 -16 208
    WIRE -80 272 -80 288
    WIRE -80 288 -16 288
    WIRE -80 208 -16 208
    WIRE -16 288 -16 336
    WIRE 48 224 48 144
    WIRE 48 144 -16 144
    WIRE 48 304 48 400
    WIRE 48 400 336 400
    WIRE 112 240 112 224
    WIRE 112 224 160 224
    WIRE 160 192 160 224
    WIRE 160 224 192 224
    WIRE 192 288 192 320
    WIRE 192 320 112 320
    WIRE 112 320 112 336
    WIRE 48 144 48 32
    WIRE 112 32 144 32
    WIRE 160 96 208 96
    WIRE 432 400 464 400
    WIRE 464 400 464 416
    WIRE 256 128 256 96
    WIRE 256 96 336 96
    WIRE 432 96 464 96
    WIRE 336 128 336 96
    WIRE 336 96 368 96
    WIRE 336 208 336 400
    WIRE 336 400 368 400
    WIRE 336 400 336 448
    WIRE 256 192 256 336
    WIRE 288 448 336 448
    WIRE 208 448 160 448
    WIRE 160 448 160 464
    WIRE 208 32 208 96
    WIRE 208 96 256 96
    WIRE 464 96 464 16
    WIRE 464 16 560 16
    FLAG -16 336 0
    FLAG 112 336 0
    FLAG 464 416 0
    FLAG 256 336 0
    FLAG 160 464 0
    FLAG 560 16 ANT
    IOPIN 560 16 Out
    SYMBOL polcap -96 208 R0
    WINDOW 3 24 64 Left 0
    SYMATTR Value 33µ
    SYMATTR InstName C1
    SYMATTR Description Capacitor
    SYMATTR Type cap
    SYMATTR SpiceLine V=10 Irms=60m Rser=2.3 MTBF=1000 Lser=0 mfg="Nichicon"
    pn="UPR1A330MAH" type="Al electrolytic" ppPkg=1
    SYMBOL res -32 192 R0
    SYMATTR InstName R1
    SYMATTR Value 5.6k
    SYMBOL res 32 208 R0
    SYMATTR InstName R2
    SYMATTR Value 15k
    SYMBOL res 96 224 R0
    SYMATTR InstName R3
    SYMATTR Value 470
    SYMBOL npn 96 96 R0
    SYMATTR InstName Q1
    SYMATTR Value 2N2222
    SYMBOL Misc\\xtal 112 16 R90
    WINDOW 0 0 32 VBottom 0
    WINDOW 3 32 32 VTop 0
    SYMATTR InstName C3
    SYMATTR Value 3.56169600e-014
    SYMATTR SpiceLine Rser=3.56169600e-014 Lser=0.0555779237 Cpar=8.90424001e-012
    SYMBOL ind 320 112 R0
    SYMATTR InstName L1
    SYMATTR Value 2.5µh
    SYMATTR SpiceLine Ipk=1
    SYMBOL voltage 304 448 R90
    WINDOW 0 -32 56 VBottom 0
    WINDOW 3 32 56 VTop 0
    WINDOW 123 0 0 Left 0
    WINDOW 39 0 0 Left 0
    SYMATTR InstName V1
    SYMATTR Value 9
    SYMBOL polcap 144 48 R270
    WINDOW 0 0 32 VBottom 0
    WINDOW 3 32 32 VTop 0
    SYMATTR InstName C4
    SYMATTR Value 0.01µ
    SYMATTR Description Capacitor
    SYMATTR Type cap
    SYMATTR SpiceLine V=10 Irms=60m Rser=2.3 MTBF=1000 Lser=0 ppPkg=1
    SYMBOL polcap 176 224 R0
    WINDOW 3 24 64 Left 0
    SYMATTR Value 0.01µ
    SYMATTR InstName C2
    SYMATTR Description Capacitor
    SYMATTR Type cap
    SYMATTR SpiceLine V=10 Irms=60m Rser=2.3 MTBF=1000 Lser=0 ppPkg=1
    SYMBOL polcap 240 128 R0
    WINDOW 3 24 64 Left 0
    SYMATTR Value 100µ
    SYMATTR InstName C5
    SYMATTR Description Capacitor
    SYMATTR Type cap
    SYMATTR SpiceLine V=10 Irms=60m Rser=2.3 MTBF=1000 Lser=0 ppPkg=1
    SYMBOL polcap 368 112 R270
    WINDOW 3 24 64 Left 0
    SYMATTR Value 100µ
    SYMATTR InstName C6
    SYMATTR Description Capacitor
    SYMATTR Type cap
    SYMATTR SpiceLine V=10 Irms=60m Rser=2.3 MTBF=1000 Lser=0 ppPkg=1
    SYMBOL polcap 368 416 R270
    WINDOW 3 24 64 Left 0
    SYMATTR Value 0.01µ
    SYMATTR InstName C7
    SYMATTR Description Capacitor
    SYMATTR Type cap
    SYMATTR SpiceLine V=10 Irms=60m Rser=2.3 MTBF=1000 Lser=0 ppPkg=1
    TEXT -98 514 Left 0 !.tran 0 10m 0 startup
    TEXT -128 464 Left 0 !.option plotwinsize=0

    ------ snip end of file ------
     
  2. Rich Grise

    Rich Grise Guest

    I'd like to know where you expect to get a 35.61696 femtoHertz crystal. ;-)

    Cheers!
    Rich
     
  3. Andrew Holme

    Andrew Holme Guest

    [snip]

    It'll never oscillate with 33uF and 100uF capacitors grounding the base and
    collector. After reducing these, and increasing L1, I got it to oscillate
    but not at 3.5MHz. I haven't checked the crystal model. I tried the
    crystal parameters from the LTSpice "Pierce.asc" demo in your circuit but
    that didn't work either.

    Most people seem to make Pierce oscillators with a JFET.

    I read that simulating high-Q resonators is difficult in Spice.
     
  4. dd

    dd Guest

    I have not run your listing on LT spice but have experience of crystal
    oscillators in LT.
    The crystal oscillator regenerates narrow band noise every cycle to
    build oscillation a crystal with Q 1 million may take 100 milliseconds
    to start to full amplitude i.e. 100000cycles. Depends on degree of
    excess loop gain)
    Spice under transient conditions calculates many times for each cycle
    hence the start up difficulty. LT has fiddle factors that you can change
    but the results are iffy.
     
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