Sensor Circuits - The Electronic Nose Artificial Olfaction Technology - page 186

Fig. 7.8 a Summing amplifier. b Summing amplifier

Fig. 7.9 Differential

amplifier

two independent sources. A differential amplifier is commonly used as a noise
rejection circuit (i.e., sensitive signals need to be amplified, when signal-carrying
cables may pass through noisy environments, where signal-carrying cables may be
extremely long, etc.). This circuit is useful in high-pass filter circuits. Each signal
connection may be affected by noise or ''pick-up,'' but if they closely follow the
same path (being twisted together, for example), they will pick up the same
amount of noise. Integrity of sensitive or low-level signals may be compromised
by the use of general ''ground'' as one ''side'' of the signal connection.
V out ¼ R R 1 V b þ 1 þ R R 1

V a ,

R x
R x þ R a

If R a = R 1 and R F then

V out ¼ð V a V b Þ R R 1