Hello!
I'm making a function generator with an AD9833 and an Arduino Nano. I want to make the offset voltage, gain, frequency and waveform digitally controlled, but I'm stuck at the amplifier part. I thought of using a digital pot, but they are hard to get a hold of where I live and I read that they can't really handle high(ish) frequencies well. Then I thought that maybe I could have a fixed gain op-amp and control the input signal; I set the op-amp gain at 2, connected the signal to a voltage divider with a MOSFET, instead of the low side resistor. In theory, changing the Vgs, I should be able to control resistance and the gate is easy to control with a microcontroller, but after I made the circuit on a breadboard, the output signal was DC.
I came across some VCA (voltage controlled amplifier) ICs, but I am avoiding going that route, since I want to finish this project soon.
I would love to hear your suggestions on how I can accomplish this!
maybe i'm misunderstanding your question, but could'nt you use a pga? (programable gain amplifier)?
my "favorite" pga is the pga281.
here are some options on digikey: Digikey PGA's
User_temp:
I came across some VCA (voltage controlled amplifier) ICs, but I am avoiding going that route, since I want to finish this project soon.
= Not clear
This is the easiest way, you can control gain the same way as LED brightness = PWM with regulated pulse width + capacitor = regulated DC voltage use that to feed pin 4 of TDA7052.
This is what I tried, but with a MOSFET. I'll try using a JFET and see how it works.
Thanks!
79galinakorczak:
= Not clear
This is the easiest way, you can control gain the same way as LED brightness = PWM with regulated pulse width + capacitor = regulated DC voltage use that to feed pin 4 of TDA7052.
I meant that shipping takes around 2 months and I don't want to wait that long.
Also, I've thought of using an audio amp, but they usually work to about 20Khz, so the frequencies of more than that won't probably work.
Still, thanks for the suggestion! I'll look into audio amps and see if they have frequency capabilities I need.
What about a switched attenuator network? Normally you'd want some boosting of level
from a DDS chip anyway so a VGA like for instance the AD8260 makes more sense than
just attenuation, although you could boost the output into a switched attenuator network.
A digipot with low resistance value like 1k is going to have a reasonable bandwidth, BTW,
there's nothing special about them, other than a bit of stray capacitance, they are simply
resistive.
Post#3
Put a capacitor between R2 and R1 and connect R2 to Vcc through 20k resistor.
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