why is it hard to get a high gain in high frequency?

Hi all
Can anyone explain why it is hard to get a high gain for single transistor amplifier? I am using .13 micro transistor and found it is very hard to get a high gain for 1G hz frequency, The dc voltage I used is 1.2 V. It is nice if I can get a 20 gain. Any suggestions?
Thanks

If you want gain all you need to do is put a large resistor at the output. But then when you do that you will have a RC pole which brings down your frequency. The tradeoff is gain to bandwidth. That's why people talk about gain-bandwidth product and sometimes ask what the Ft of your transistor is. What do you think?

That is all about the RC loading effect. But in general, the smaller the MOSFET size (L), the higher the gm, so you don't need high load resistance to achieve high gain (Gm*R). I use 0.13um NMOS can achieve 20dB gain upto 2GHz.

good call.

All in all,GBW talks...

Why are you talking about amplifier with resistive load...? To get high gain we need high differential resistance load, like transistor current source or inductor. With such the loads it is not so difficult to get high gain at high freq.

you can put a tank circuit in your output the inductor will resonate with your output nodes capacitors and in resonance frequency(1ghz) it wiill provide high impedance and will increase your gain. i think it is simple to get such gain in 1ghz.

Did you find this post helpful? Click: