Digital amplitude modulating

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.

Reply to
Adam
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Start here:

http://en.wikipedia.org/wiki/Modulation
Reply to
John Fields

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.

Reply to
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.

Reply to
MooseFET

He said _amplitude_ modulation.

Reply to
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.

Reply to
MooseFET

sigh.

Reply to
Simon S Aysdie

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

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

Reply to
Adam

On a sunny day (Thu, 13 Sep 2007 02:50:56 -0700) it happened Adam wrote in :

+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.

Reply to
Jan Panteltje

On a sunny day (Thu, 13 Sep 2007 10:54:37 GMT) it happened Jan Panteltje wrote in :

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

Reply to
Jan Panteltje

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

-----+---------/\\/\\-------+--------/\\/\\-------+------ ! ! ! ! ---!-\\ ! ----O ! >------------

Reply to
MooseFET

On a sunny day (Thu, 13 Sep 2007 05:52:36 -0700) it happened MooseFET wrote in :

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.

Reply to
Jan Panteltje

On a sunny day (Thu, 13 Sep 2007 05:52:36 -0700) it happened MooseFET wrote in :

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.

Reply to
Jan Panteltje

Not loading a circuit means not extracting any energy.

Oxymoronically, now I understand your confusion.

Reply to
Simon S Aysdie

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.

Reply to
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.

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.

Reply to
MooseFET

On a sunny day (Thu, 13 Sep 2007 19:13:52 -0700) it happened MooseFET wrote in :

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

+5 | [ ] |----------------> analog audio ||O carbon | microphone ///
Reply to
Jan Panteltje

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.

Reply to
MooseFET

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

Yes, carbon mike rules!

Reply to
Jan Panteltje

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

Reply to
Rich Grise

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