BIOPOTENTIAL AMPLIFIERS - Design and Development of Medical Electronic Instrumentation - page 8

Rf

If

-Vcc

Rin

A

-
+

Iin

+Vcc

Vout

Vin

Figure 1.5 Noninverting op-amp voltage ampli fi er; also known as a noninverting follower.

-VCC

-
+

+VCC

Vin Vout

Figure 1.6 A unity-gain buffer is a special case of the noninverting voltage amplifier in which the
resistance ratio is R f / R in 0, which translates into unity gain. This configuration is often used in bio-
medical instrumentation to buffer a high-impedance signal source.

ULTRAHIGH-IMPEDANCE ELECTRODE BUFFER ARRAYS

A group of ultrahigh-impedance, low-power, low-noise op-amp voltage followers is com-
monly used as a bu er for signals collected from biopotential electrode arrays. These

circuits are usually placed in close proximity to the subject or preparation to avoid contamina-
tion and degradation of biopotential signals. The circuit of Figure 1.7 comprises 32 unity-gain

ff