# Why is frequency response an important characteristic of an amplifier?

1. Oct 11, 2011

### S_Flaherty

Why is frequency response an important characteristic of an amplifier?

in this situation we are using a transistor and had to calculate gain using specified frequencies
and the resulting voltages through our circuit.

My understanding of contemporary electronics is not as strong as i want it to be
so even though i'm pretty sure this is a very basic question i'm still having trouble.

2. Oct 12, 2011

### 256bits

An amplifier receives an input signal and outputs as signal with an increase in magnitude.
You would want the output to have no distortion and the increase in magnitude to be constant for the range of frequencies you are interested in. ( ie a flat response is desired in certain situations such as an audio amplifier ).

An audio amplifier, such as one that would play a song from a CD, would have to have a flat response for the range of human hearing, 50 Hz to 20,000 Hz so that you could hear the music and vocals as they were recorded. A telephone response would be in the range from 200Hz to 5000Hz approximately which is the range of the human voice.

Other criteria besides amplification might include stability for example, .

Some sites:
http://www.mediacollege.com/audio/microphones/frequency-response.html

3. Oct 12, 2011

### S_Flaherty

4. Oct 12, 2011

### cepheid

Staff Emeritus
The audio amplifier was just a specific example that 256bits was giving to illustrate the more general idea that you want to avoid excessive distortion of your input signal by the amplifier, and you do this by ensuring that it has relatively constant gain across the range of frequencies you expect to be contained in your input (i.e. across the "bandwidth" of your input signal). If some frequencies in your input are attenuated because your amplifier has lower responsivity there, then obviously the amplified output signal is not going to be an accurate/faithful reproduction of the input.

5. Oct 12, 2011

### S_Flaherty

Alright now i understand. Thanks for clearing things up for me.

6. Oct 12, 2011

### jambaugh

Another point which may possibly be relevant to the OP.

Arbitrary periodic wave shapes can be resolved as a combination of frequencies (Fourier Transformation). Failure to amplify all frequencies in the bandwidth uniformly will distort the wave shape. In the example of a digital signal it may make the result more susceptible to errors.

Obviously however the problem with and answer to your question is that the importance is relative to the application. In some applications one need (or specifically desire to ) only amplify a nearly pure single frequency, for example CW transmitter for sending Morse code or IF stage in a superhetrodyne receiver (classic AM transistor radios). In other cases you need a wide bandwidth as with e.g. audio amplifiers which cover 7 to 8 octaves.

So frequency response is important for matching the amplifier to the application.