Sorry for the late reply!
Aaron,
Quote:1. Which amplifier are you designing? Anyway 50 dB gain may be doable (bandwidth will be tight), but it is not advisable. In the first place, the linearity will be very poor as any blocker is liekly to saturate the amplifier, and in the second place, its likely to be unstable. Any time S21 is more than S12 at RF frequencies, you're asking for trouble.
I have been said that I need to design an RF amp with voltage gain 50dB. However, I have searched a lot and haven't found any voltage RF amp. All RF amplifier are RF power amplifier. I wonder can I use these RF power amplifier to get voltage gain 50dB.
Quote:Why do you need to increase the amplifier's gain to 50 dB?
I need about 0.3V at the input of ADC. Maybe, I miss something!
tm123,
Quote:Trying to achieve 50dB in a single RF amplifier stage will be a fruitless effort. You will certainly need to have several cascaded stages to achieve that amount of gain at RF. Depending on whether you are using bipolar or MOS devices, a reasonable amount of gain would be 15dB per stage in my opinion.
There are always tradeoffs involved in design, so you will have to tradeoff some other performance to achieve high gain as Aaron described. Most likely you will be trading off linearity by decreasing the amplifier degeneration. Stability is always a concern at RF as well.
As a side note, there are many ways to define 'gain' of an amplifier including voltage gain, power gain, transducer gain, available gain, etc. Please make sure you understand these definitions and understand what the spec is. Always be clear on how you simulate/measure the 'gain' of any RF/microwave amplifier. I realize you specified voltage gain in this case, but since you are impedance matching at the RF amplifier input and the RF amplifier output is terminated on chip it can become confusing as to what gain you are actually quantifying.
I am learning basic concepts before designing.
How about if I use multi-stage amplifier? For example, I will use three stages, each one has a voltage gain 17dB.