Electronics Sixth Sense Resources

` Text Only Version

Useful Link for Operational Amplifiers
BBC Bitesize Revision - Design & Technology

Operational Amplifiers
One very useful Integrated Circuit or IC is the Operational amplifier.
E.g. 741, 081 etc

It is an amplifier with a very high open loop gain (100000). A very high input resistance (we call this impedance at A-Level), so that it draws very little current from its input source. A very low output resistance so it can source or sink about 10mA of current at its output. The maximum current is usually limited to about 13mA. The bandwidth for an operational amplifier is quoted as the range of frequencies for which it can amplify by the same amount.

a
	When quoting these properties we usually say:
01.	An ideal operational amplifier has infinite gain
02.	An ideal operational amplifier has infinite input resistance and draws no current at its input.
03.	An ideal operational amplifier has zero output resistance.
04.	An ideal operational amplifier has an infinite bandwidth.
a

Voltage Amplifiers produce an output voltage, which is a larger version of its input voltage. i.e. The output voltage is proportional to the input voltage.


	The output voltage however cannot exceed the saturation voltage (slightly lower than supply rail) voltage of the operational amplifier. The gain of the amplifier is given by When no link occurs between the output and the input the op-amp is said to have an open look gain, which is about 100 000. (no feedback) With feedback this gain is known as closed loop and can be controlled by the resistors in the feedback connection. At GCSE op-amps are used in two ways a) As Inverting Amplifiers -with negative feedback b) As Comparators – comparing voltages and hence no feedback.