Class C amplifier for uV levels?

[neazoi]

I have designed this class-C amplifier which works on both input sinewave peaks.
As expected, this waveform is produced only when the input sine peaks are at about 0.7v.

Is there any way I can make this (or another class-C) amplifier working in the uV levels?

 

[BigBoss]

-There is no way to build a Class-C Power Amplifier working at uV level.(Transistors won't work at that level)
-Why you use Class-C Amplifier ?? This generally is used for High Efficiency Power Amplifiers. Do you really need this ?

 

[neazoi]

-There is no way to build a Class-C Power Amplifier working at uV level.(Transistors won't work at that level)
-Why you use Class-C Amplifier ?? This generally is used for High Efficiency Power Amplifiers. Do you really need this ?

I thought it could be used as a simple "dead zone" amplifier on HF (2-30MHz), where only the higher level signals could be amplified (the ones that cause the transistor to conduct). I just wanted to see if this threshold level could be reduced.

Danadakk in this thread https://www.edaboard.com/threads/rf-detector-with-my-comparator.396013/ post #7 made the transistors to start conducting from lower levels (although not uV). I was hoping that something similar could be done in a class-C amplifier, so that the level of the peaks the amplifier amplifies is reduced to much lower levels.

Obviously a class-A preamplifier before a class-C can be used to amplify signals to the class-C threshold level, but this raises IMD (signals nonlinear mixing) problems and this is exactly what I want to avoid.

One thing that I want to know about class-C amps, is, how will a class-C circuit behave under the presence of a strong amplitude sine in one frequency (that is able to trigger the amplifier) and a very low amplitude signal on another frequency? At the time that the amplifier conducts (due to the presence of the high level signal), it would amplify both signals, the low and the high ones, isn't that true?

 

[G4BCH]

One thing that I want to know about class-C amps, is, how will a class-C circuit behave under the presence of a strong amplitude sine in one frequency (that is able to trigger the amplifier) and a very low amplitude signal on another frequency? At the time that the amplifier conducts (due to the presence of the high level signal), it would amplify both signals, the low and the high ones, isn't that true?

What you describe here is an active mixer. The low level signal will be 100% modulated by the high level signal. The output will be both signals together with the sum and difference frequencies. There will also be harmonic sum and differences present.
Putting non linear devices in the signal path of a receiver is a bad idea, Receiver designers go to great length to ensure that the signal path is as free from distortion as possible.

 

[BigBoss]

As far as I understand, you intend to amplify a signal that exceeds a certain power level, right ??
If it's so, two questions should be answered.
-The system has to get the information about signal strength
-And the same system will amplify this signal

I believe a RSSI+Amplifier with Inhibit Feature can work.
RSSI will detect the signal level and the rest of the circuit amplifies the signal with this inhibit feature.

C-Class amplifier can work but it creates so many harmonics and driving level is pretty high.

 

[neazoi]

As far as I understand, you intend to amplify a signal that exceeds a certain power level, right ??
If it's so, two questions should be answered.
-The system has to get the information about signal strength
-And the same system will amplify this signal

I believe a RSSI+Amplifier with Inhibit Feature can work.
RSSI will detect the signal level and the rest of the circuit amplifies the signal with this inhibit feature.

C-Class amplifier can work but it creates so many harmonics and driving level is pretty high.

You are in the right path. These are the problems I encountered with a class-C amplifier indeed.
It would be really helpful if you can give me a circuit example, anything you can find on the web etc, as a starting point to get me started with it on the right path.

 

[FvM]

Class-C doesn't amplify µV signals. If you bias it respectively, it becomes class-A (for µV signals) or class-AB (for gigher level).

It's still umclear what you want to achieve.

 

[BigBoss]

You are in the right path. These are the problems I encountered with a class-C amplifier indeed.
It would be really helpful if you can give me a circuit example, anything you can find on the web etc, as a starting point to get me started with it on the right path.

OK, look at this Power Detector here.

https://www.analog.com/en/products/ad8362.html#product-overview

It has very wide dynamic range and it's pretty accurate. There are lot of information how to implement in datasheet.
All you need si to use a Comparator at DC output of this detector and when a well defined level is exceeded, the comparator will inhibit the amplifier.

TRF37A73 data sheet, product information and support | TI.com

TI’s TRF37A73 is a 1 to 6000 MHz 12dB RF Gain Block Amplifier with Powerdown Pin. Find parameters, ordering and quality information

www.ti.com

TRF37A73 has a Power Down input and this can be connected to comparator output.

 

[neazoi]

OK, look at this Power Detector here.

https://www.analog.com/en/products/ad8362.html#product-overview

It has very wide dynamic range and it's pretty accurate. There are lot of information how to implement in datasheet.
All you need si to use a Comparator at DC output of this detector and when a well defined level is exceeded, the comparator will inhibit the amplifier.

TRF37A73 data sheet, product information and support | TI.com

TI’s TRF37A73 is a 1 to 6000 MHz 12dB RF Gain Block Amplifier with Powerdown Pin. Find parameters, ordering and quality information

www.ti.com

TRF37A73 has a Power Down input and this can be connected to comparator output.

Hm...
What if strong signals on other frequencies, are presented in the input of the RSSI? This will five a false triggering on the actual signal we want to level-amplify.

You made me think now, how about a BPF, followed with a single transistor preamplifier, which drives an envelope detector. The envelope detector output drives a comparator and it's output allows or shunts (through a transistor) the signal output?
As long as the input signal level is high enough (again a filter is needed), the output will not be shunted to ground.

 

[BigBoss]

Hm...
What if strong signals on other frequencies, are presented in the input of the RSSI? This will five a false triggering on the actual signal we want to level-amplify.

You made me think now, how about a BPF, followed with a single transistor preamplifier, which drives an envelope detector. The envelope detector output drives a comparator and it's output allows or shunts (through a transistor) the signal output?
As long as the input signal level is high enough (again a filter is needed), the output will not be shunted to ground.

RF Power Detector can already not distinguish the incoming frequencies where they are coming from. It measures Average Power Level of all incoming signal(s). In order to discriminate a particular signal, you have to use either a sharp BPF or Mixer+Oscillator and BPF ( or Crystal, SAW or any other very selective filter) to measure IF signal.
By this way, you will able to measure and control your particular signal.