# Biasing amplifiers and what they do to the input and output voltages

1. Jun 7, 2012

### therajinator

If we have a input voltage that has a voltage higher then the linear region of the amplifier characteristics graph, what does amplifier biasing exactly do to the wave so there is no clipping, distortion or cut-offs and saturations.

2. Jun 7, 2012

### Studiot

Goodmorning therajinator and welcome to Physics Forums,

This part makes no sense.

This part makes sense on its own

What do you really mean?

3. Jun 7, 2012

### sophiecentaur

Correct biasing is important, of course but you also must not over-drive the input outside the linear region for the output. All things being equal, you would choose the bias voltage so that the average (DC) output signal value is 'half way' in between the limits of the output stage.
That's a very simple answer but is it enough?

4. Jun 7, 2012

### therajinator

okay let me mkae it clearer... this is in regards to a question in a practice vce physics unit 3 exam.

There is a transfer characteristics graph of a transistor amplifier. the linear region of the input voltage is between 1mV and 7mV's. while the output is between 1V and 9V's.

The question asks: an AC signal, whose voltage waveform, i snow fed into the amplifier and an undistorted amplified signal is obtained. What is the ideal DC voltage that should be provided to the input signal to avoid distortion? explain your answer, using the term bias in an appropriate manner.

The input graph looks like a sin wave and has a p-p voltage of 8mV and a frequency of 125Hz.

Thanks

5. Jun 8, 2012

### sophiecentaur

Put your bias point at a value that produces a DC output which is half way up the linear region. You can read that off your graph? (The shape of the input waveform is not relevant if you are dealing with (aiming at) a linear amplifier.

6. Jun 8, 2012

### therajinator

thanks guys I understand now, the middle of the amplifier characteristics graph is called the quiescent point which adjusts the input AC voltage so it's in the linear region.