I've designed this circuit as an attempt to make a radio receiver that can receive AM signals and turn them into DC voltage levels based on the amplitude of the carrier wave.

To explain it simply: the two op amps at the bottom right act kind of like a differentiator, with the capacitor acting as a time delay. This "block" outputs an on signal whenever the slope of the wave is downward, which is very soon after it peaks.

This signal goes into the two comparators ahead of them which work as a timer, giving the circuit time to sample the amplitude and then stop before it gets too low to be useful.

During this window, that AND gate gets activated and triggers the sample and hold circuit you see at the top. The capacitor samples it (the resistor seemed to prevent spiking), and then the output op amp has that transistor to help smooth it a bit more.

My primary concern is that I don't think the BJTs used to control the sample and hold circuit would actually work. I tried using an n channel MOSFET like in most sample and hold circuits but, on this simulator anyways, the MOSFET didn't block reverse current, so the capacitor would always charge to a negative voltage when the radio wave went negative. I'm also unsure of whether the values for the capacitor would work as well as they did here. I'm using falstad which isn't exactly known for its accuracy.

Note that the antenna was amplifier by the simulator and only had one frequency, hence the absence of filters and amplifiers. I'll add those in the actual circuit.

I plan to use TL072s for the op amps.

Anyone with expertise weighing in would be a big help.

 

I think you need to add low-pass filtering to the input signal path before the differentiator.

 

I think you need to add low-pass filtering to the input signal path before the differentiator.

Why is that?

 

Why is that?

Because differentiators amplify noise in real life.

 

Indeed it does not seem reasonable that the complex circuit shown will deliver the intended results.
A more effective scheme to provide the stated goal results has been in service for many years.

 

Indeed it does not seem reasonable that the complex circuit shown will deliver the intended results.
A more effective scheme to provide the stated goal results has been in service for many years.

Why would that be?

 

There is nothing to discharge the 80 nF capacitor.

AND - Discussing this circuit without reference designators for each component will be very difficult.

ak

 

Another sad troll projecting and trying to irritate others.

Even homelessness would make your parents proud of you at this point.

After those comments, I can see why you have that moniker.

 

The very earliest radio receivers dd exactly what the TS states is the goal: to convert the amplitude of the RF signal into a DC level.
Of course it is a rapidly changing DC level and it carries the signal that modulated the amplitude of the radio frequency signal.

 

Studying your schematic I don't see how it would receive / rectify an AM signal, Bback when I was a new techling I focused on radios. as it is I don't see how you would tune a specific frequency with your antenna.

 

Between the two BJTs (Collector to Base), there should be a resistor like 5KOhm; otherwise they would greatly affect the operation of the top-left OPAMP. The 5Ohm resistor on the right-hand side that drives the Base of the lower BJT is also too low; 5KOhm might be more appropriate. If all the R/C values magically fit, the window may capture part of the envelop of the input signal.

 

One more thing is the consideration of the incoming signal levels: They are normally in the microvolts levels, and yet only one of the amplifiers is configured to have more than unity gain.
Given that the signal arriving from even a good and resonant antenna will include a vast spectrum of wideband noise, it does not seem that the circuit can even in theory provide a signal from a single source.
Aside from all of that, the circuit drawing could certainly be much better arranged. As it stands, the lower right quadrant is messy and takes a lot of effort to even follow. The whole creation was drawn but not "designed", as that term is usually understood to imply.