What is the difference between Rf Gain Blocks & IF Gain Blocks?

Question

As advertised on websites of large manufacturers like Analog Devices And Texas Instruments

I am aware of the difference between an IF stage and an RF stage, however, I was curious if there was any any other differences. Say I have a 50-500MHz IF gain block, is it OK to either use it in a 200MHz IF stage of a Tx system, or (and this is my question) use it in a 200MHz RF stage of another system?

Answer 1

Aside from their operating frequency, for all practical purposes, there is not much difference between the internal schematics of RF and IF amplifiers. But you will find that components designed for use as IF amplifiers have characteristics that are better optimized for their intended use, and likewise for RF amplifiers. So if you are planning to use a component in an RF stage, you might want to pay more attention to a component's dynamic range, isolation, noise figure, input/output impedance, and other parameters that might be especially important in that application. An RF component is more likely to be better optimized for your needs in an RF stage. Analogously for an IF amplifier component. But if a component's parameters (including cost) are all a good match for your circuit design, then pay no attention to the RF versus IF label that the manufacturer has attached to it.

Answer 2

Again - I am not an expert on such things, but my understanding of the basic differences between an RF stage amplifier and an IF stage amplifier, is that:

• An RF stage amplifier needs to amplify all the frequencies in the current band, to allow tuning across the whole band.
• An IF stage amplifier is used where the signals from the current band have been downconverted (or upconverted) to a single fixed frequency (the IF), and one of the main jobs of the IF amplifier is to remove unwanted frequencies outside of an extremely narrow band of frequencies, centred on the IF.

So to answer the original question, if the amplifier block is specifically designed to be a 200MHz IF amplifier, check what the bandwidth of the amplifier is at that frequency. if it really is an IF amplifier block, it could easily have a bandwidth of +/- 10kHz or less (so allowing 190-210MHz through, with a fairly sharp cutoff outside that range).