SEED Guides Unit Selection - Operational Amplifiers < >

1. THE INVERTING AMPLIFIER:

The input signal is applied to the inverting (-) input (see Fig 4.1). The output is out of phase by 180š with respect to the input.

N.B. a non-inverting amplifier may not be used as an attenuator. An inverting amplifier may have a gain which is less than one and can be used as an attenuator.

3 and 4. A C AMPLIFIERS:

To amplify only AC signals "roll off" the gain to unity at frequencies close to DC, to prevent saturation by DC offset voltages. The circuit for an inverting AC amplifier is shown in Fig. 4.3.

6 and 7. SUMMING AMPLIFIERS:

The circuit may be extended to have as many inputs as required.

If resistor values are chosen for natural bi-nary weighting, the circuit can be used as a digital to analogue (D/A) converter (Fig. 4.7). However, the wide range of resistor values needed to provide a binary weighting prevents expansion to more than about 4 bits, due to temperature tracking problems.

8 and 9. DIFFERENTIAL AMPLIFIERS:

Fig. 4.8 shows equal sets of resistors for both input and feedback. A useful property of a differential amplifier is that it rejects common-mode signals originating at the signal source as described in A5.

The output is the amplified difference between the two input signals: