Cascaded BJT RF Amplifier

Thread Starter

tunneldiode

Joined Feb 12, 2021
2
Hello,

I'm working on a hobby project to design a 10MHz-1GHz bandwidth amplifier with 200x voltage gain (typical input is -12.5mV pulse with 500ps rise time). My design intent is to cascade the BFR193 (maybe 4 stages) to achieve the gain and bandwidth I desire. Any suggestions on where to find a design guide for such a system? I did look at https://forum.allaboutcircuits.com/...or-bfr183-and-193.190424/page-2?cb=1705203775.

Thanks!
 

MisterBill2

Joined Jan 23, 2018
18,415
Most RF amplifiers that I have seen use either resonant circuits or just inductive loads. And inductive reactance is frequency dependent. And every bit of capacitive reactance is also frequency dependent. 10 MHz to to 1000,000MHz (one GHz) is a huge bandwidth. and with a gain of 200x = 40 dB, that will be either very complex or else have a lot of compromises.
Also, it seems that I can not open a ".asc file, I think that is a simulator format, I don't do simulators.
And understand that many simulators do not adequately reflect reality. Pars do not burn out in a simulator, nor suffer from a lot of other real world problems.
 

Bordodynov

Joined May 20, 2015
3,179
I agree with MisterBiil2. I think you will not be able to implement your amplifier in which there will be no oscillations.
I have a note about your modeling:
1. For simulation, it is necessary to use full-fledged models that take into account the parasitic elements of the transistor housing.
2. There is no signal source with zero resistance!
 

Tesla23

Joined May 10, 2009
542
If it's just for a hobby project, give up on the BJT and use monolithic gain blocks, they are only slightly more expensive than your BJTs and much easier to use. MiniCircuits, Analog Devices, Infineon and others have them. For starters look at GALI-33 or BGA616. You will need some care with the layout to keep it stable, but 46dB is probably doable.

If you want to go down the discrete path, look at resistive feedback amplifiers, this is what most of the cheap gain blocks are. This sort of circuit:

1705302105505.png

You can use either a BJT or FET (with appropriate biassing)
 
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