Digital amplitude modulating

[Adam]

Hello there,
I am jus a newbie
Well I want to design a digital amplitude modulator circuit based on
CMOS chips. At the moment I have no idea which one though. Can an
expert in the field help me and direct me to suitable chip for the
job?
I want it for frequencies just below 200 kHz.
Beside, I prefer single supply rather than split one's.

Thanks a lot for any direction.

 

[John Fields]

Hello there,
I am jus a newbie
Well I want to design a digital amplitude modulator circuit based on
CMOS chips. At the moment I have no idea which one though. Can an
expert in the field help me and direct me to suitable chip for the
job?
I want it for frequencies just below 200 kHz.
Beside, I prefer single supply rather than split one's.

Thanks a lot for any direction.

 

[Simon S Aysdie]

Hello there,
I am jus a newbie
Well I want to design a digital amplitude modulator circuit based on
CMOS chips. At the moment I have no idea which one though. Can an
expert in the field help me and direct me to suitable chip for the
job?
I want it for frequencies just below 200 kHz.
Beside, I prefer single supply rather than split one's.

Thanks a lot for any direction.

You're vague on what you mean by "digital amplitude modulator."

Anyway, if you want basic DSB-SC AM, then any old CMOS transmission
gate (driven by an LO for the chopping) will do and it is an
extraordinarily simple circuit.

If you want IQ (quadrature) modulation, then you'll need an orthogonal
chopping source (LO) and another transmission gate. You'd have to
combine (sum) the chopper outputs correctly, but it is more or less
just two basic DSB-SC modulators with the quadrature outputs summed
correctly. A "perfect" 90 degree LO can be had by a div-by-4 D-FF
circiut.

Pretty dog-gone easy for your frequency requirement.

 

[MooseFET]

Hello there,
I am jus a newbie
Well I want to design a digital amplitude modulator circuit based on
CMOS chips. At the moment I have no idea which one though. Can an
expert in the field help me and direct me to suitable chip for the
job?
I want it for frequencies just below 200 kHz.
Beside, I prefer single supply rather than split one's.

Thanks a lot for any direction.

Consider an AND or OR gate. Look at what it does to the modulation
and carrier signals when you hook them to the inputs.

If those aren't right for what you need try an XOR gate.

If still no luck, look at 74HC4051, 52 and 53.

 

[Simon S Aysdie]

Consider an AND or OR gate. Look at what it does to the modulation
and carrier signals when you hook them to the inputs.

If those aren't right for what you need try an XOR gate.

If still no luck, look at 74HC4051, 52 and 53.

He said _amplitude_ modulation.

 

[MooseFET]

He said _amplitude_ modulation.

Yes and look at what all of those do.

AND gates AM modulate with carrier.

XORs do double side band supressed carrier.

The OR produces an inverted sort of AM

The 405X can do lots of other things.

 

[Simon S Aysdie]

Yes and look at what all of those do.

AND gates AM modulate with carrier.

XORs do double side band supressed carrier.

The OR produces an inverted sort of AM

The 405X can do lots of other things.

sigh.

 

[Adam]

Can some show me an amplitude modulator made by those chips?

what about 4066 Quad Bilateral Switch
any schematic for it please?

 

[Jan Panteltje]

Can some show me an amplitude modulator made by those chips?

what about 4066 Quad Bilateral Switch
any schematic for it please?

+2.5V 0V
| |
R1 [ ] 100k | 74HC4053
| 0 \ C2 100pF
LF --------||----------------0 \ 0--------------||----- 1MHz AM modulated
C1 1uF | |
| [ ] R2 10k
Audio 5V pp RF 0V / 5V |
square wave ///
1MHz
When no audio, the switch swicthes between 0V and +2.5V,
resulting in a 2.5V pp RF carrier.

When audio is present, the peak amplitude of the RF carrier is set by it.
C2 R2 for a high pass.
Better use a LC there.

 

[Jan Panteltje]

Can some show me an amplitude modulator made by those chips?

what about 4066 Quad Bilateral Switch
any schematic for it please?

+2.5V 0V
| |
R1 [ ] 100k | 74HC4053
| 0 \ C2 100pF
LF --------||---------A -----0 \ 0--------------||----- 1MHz AM modulated
C1 1uF | |
| [ ] R2 10k
Audio 5V pp RF 0V / 5V |
square wave ///
1MHz
When no audio, the switch swicthes between 0V and +2.5V,
resulting in a 2.5V pp RF carrier.

When audio is present, the peak amplitude of the RF carrier is set by it.
C2 R2 for a high pass.
Better use a LC there.

Eh, correction, better have an opamp 1x buffer in 'A',
else R 2 shorts much of the signal.

 

[MooseFET]

Can some show me an amplitude modulator made by those chips?

what about 4066 Quad Bilateral Switch
any schematic for it please?

+2.5V 0V
| |
R1 [ ] 100k | 74HC4053
| 0 \ C2 100pF
LF --------||----------------0 \ 0--------------||----- 1MHz AM modulated
C1 1uF | |
| [ ] R2 10k
Audio 5V pp RF 0V / 5V |
square wave ///
1MHz
When no audio, the switch swicthes between 0V and +2.5V,
resulting in a 2.5V pp RF carrier.

When audio is present, the peak amplitude of the RF carrier is set by it.
C2 R2 for a high pass.
Better use a LC there.

If the input is an analog signal as you show, the 4053 is a better
part for this job:


-----+---------/\/\-------+--------/\/\-------+------
! ! !
! ---!-\ !
----O ! >------------
<------------------!+/
GND ------O


This circuit doesn't have any of the problems with loading the input
and passing the modulation signal, the analog switch circuit you
suggested would have.

The OP, however asked for digital. An AND gate would do it for a
digital input.

 

[Jan Panteltje]

Can some show me an amplitude modulator made by those chips?

what about 4066 Quad Bilateral Switch
any schematic for it please?

+2.5V 0V
| |
R1 [ ] 100k | 74HC4053
| 0 \ C2 100pF
LF --------||----------------0 \ 0--------------||----- 1MHz AM modulated
C1 1uF | |
| [ ] R2 10k
Audio 5V pp RF 0V / 5V |
square wave ///
1MHz
When no audio, the switch swicthes between 0V and +2.5V,
resulting in a 2.5V pp RF carrier.

When audio is present, the peak amplitude of the RF carrier is set by it.
C2 R2 for a high pass.
Better use a LC there.

If the input is an analog signal as you show, the 4053 is a better
part for this job:


-----+---------/\/\-------+--------/\/\-------+------
! ! !
! ---!-\ !
----O ! >------------
<------------------!+/
GND ------O


This circuit doesn't have any of the problems with loading the input
and passing the modulation signal, the analog switch circuit you
suggested would have.

The OP, however asked for digital. An AND gate would do it for a
digital input.

True, however if the audio (modulating signal) was _also_ digital,
in the sense of say 8 bits wide, then you can in the above circuits
simply use 8 resistors (or R2R or course):

D0 128k -|
D1 64k -|
D2 32k -|
D3 16k -|_____________||_______ analog audio to your circuit.
D4 8k -| ||
D5 4k -|
D6 2k -|
D7 1k -|

Now we have good music quality AM

You could also use a AD converter and use the reference as RF input,
'digital potentiometer', I have done that too.

This is something an AND gate will not do, only useable for morse type
on /of AM.

 

[Jan Panteltje]

On a sunny day (Thu, 13 Sep 2007 05:52:36 -0700) it happened MooseFET
<[email protected]>:

Actually this gives me an idea with AND gates:

8 bits digital audio AM modulator:

D0 --------------------------- AND --- 128k ---
RF -- |
|
D1 --------------------------- AND --- 64k ---
RF -- |
|
D2 --------------------------- AND --- 32k ---|
RF -- |
|
D3 --------------------------- AND --- 16k ---|
RF -- |
|--------||------ RF
D4 --------------------------- AND --- 8k ---|
RF -- |
|
D5 --------------------------- AND --- 4k ---|
RF -- |
|
D6 --------------------------- AND --- 2k ---|
RF -- |
|
D7 --------------------------- AND --- 1k ---
RF --

You could perhaps replace the ANDs with RF power amps of 1, 2, 4, 8, 16, 32, 64, and 128 W,
combine ouputs in some coupler, and use the data lines to switch these on.

 

[Simon S Aysdie]

This circuit doesn't have any of the problems with loading the input
...

Not loading a circuit means not extracting any energy.

The OP, however asked for digital. An AND gate would do it for a
digital input.

Oxymoronically, now I understand your confusion.

 

[MooseFET]

Not loading a circuit means not extracting any energy.


Oxymoronically, now I understand your confusion.

No I am not confused. It appears that you were. Like I said an AND
gate does amplitude modulation of digital signals. When the
modulating signal is high, the amplitude of the carrier on the output
is bigger (0-5V) than when the modulating signal is low. This is
exactly what the OP asked for.

 

[MooseFET]

On a sunny day (Thu, 13 Sep 2007 05:52:36 -0700) it happened MooseFET
<[email protected]>:

True, however if the audio (modulating signal) was _also_ digital,
in the sense of say 8 bits wide, then you can in the above circuits
simply use 8 resistors (or R2R or course):

D0 128k -|
D1 64k -|
D2 32k -|
D3 16k -|_____________||_______ analog audio to your circuit.
D4 8k -| ||
D5 4k -|
D6 2k -|
D7 1k -|

Now we have good music quality AM

You can do quite a bit better than that without putting the parts
count up to the moon. If you have a system clock at several times the
output frequency, you can pulse the end of the resistor on for part of
a cycle to get in between values.

You could also use a AD converter and use the reference as RF input,
'digital potentiometer', I have done that too.

This is something an AND gate will not do, only useable for morse type
on /of AM.

If you boost the high frequencies in the voice and then run it into a
comparitor and then put the AND gate on the output of the comparitor,
you can understand what is being said. It sounds really awful though.

 

[Jan Panteltje]

You can do quite a bit better than that without putting the parts
count up to the moon. If you have a system clock at several times the
output frequency, you can pulse the end of the resistor on for part of
a cycle to get in between values.

You can decrease part further by using an old carbon mike and a resistor ;-)

+5
|
[ ]
|----------------> analog audio
||O carbon
| microphone
///

 

[MooseFET]

You can do quite a bit better than that without putting the parts
count up to the moon. If you have a system clock at several times the
output frequency, you can pulse the end of the resistor on for part of
a cycle to get in between values.

You can decrease part further by using an old carbon mike and a resistor ;-)

+5
|
[ ]
|----------------> analog audio
||O carbon
| microphone
///

If you stand a little closer to the listener, you can reduce the parts
count further.

Also:

A carbon microphone between a signal gnerator and antenna will
transmit voice.

 

[Jan Panteltje]

in the sense of say 8 bits wide, then you can in the above circuits
simply use 8 resistors (or R2R or course):

D0 128k -|
D1 64k -|
D2 32k -|
D3 16k -|_____________||_______ analog audio to your circuit.
D4 8k -| ||
D5 4k -|
D6 2k -|
D7 1k -|

Now we have good music quality AM

You can do quite a bit better than that without putting the parts
count up to the moon. If you have a system clock at several times the
output frequency, you can pulse the end of the resistor on for part of
a cycle to get in between values.

You can decrease part further by using an old carbon mike and a resistor ;-)

+5
|
[ ]
|----------------> analog audio
||O carbon
| microphone
///

If you stand a little closer to the listener, you can reduce the parts
count further.

Also:

A carbon microphone between a signal gnerator and antenna will
transmit voice.

Yes, carbon mike rules!

 

[Rich Grise]

On a sunny day (Fri, 14 Sep 2007 06:23:44 -0700) it happened MooseFET

On a sunny day (Thu, 13 Sep 2007 19:13:52 -0700) it happened MooseFET
<[email protected]>:

in the sense of say 8 bits wide, then you can in the above circuits
simply use 8 resistors (or R2R or course):

D0 128k -|
D1 64k -|
D2 32k -|
D3 16k -|_____________||_______ analog audio to your circuit.
D4 8k -| ||
D5 4k -|
D6 2k -|
D7 1k -|

Now we have good music quality AM

You can do quite a bit better than that without putting the parts
count up to the moon. If you have a system clock at several times the
output frequency, you can pulse the end of the resistor on for part of
a cycle to get in between values.

You can decrease part further by using an old carbon mike and a resistor ;-)

+5
|
[ ]
|----------------> analog audio
||O carbon
| microphone
///

If you stand a little closer to the listener, you can reduce the parts
count further.

Also:

A carbon microphone between a signal gnerator and antenna will
transmit voice.

Yes, carbon mike rules!

Anybody remember last April 1, when they announced this new technology
that used acoustic waves for information transfer?

The punch line was, "turn to your neighbor, and ask him/her what today's
date is."

I don't remember the acronym, but I think I spotted it right away, at
the time.

I did a quick google search, but I think maybe these seasonal jokes
are kind of ephemeral, and don't remember the exact acronym.

Thanks,
Rich