The measurement of differential signals is quite common across many applications and are especially prevalent in biopotential sensors, for example electrocardiograms. Biopotential sensors can often be high impedance and require low input bias and current noise. Instrumentation amplifiers, introduced in the previous section, are commonly used to condition differential signals from biopotential sensors The LMC608x are a great choice in particular due to the extremely low input bias current and current noise, high common-mode rejection ratio (CMRR) and low power. A high performance instrumentation amplifier can be achieved by using the LMC608x and a pair of RES11A matched resistors.

Figure 6-7 Instrumentation Amplifier With the RES11A

Figure 6-7 shows an instrumentation amplifier design with a gain of 10V/V. The first RES11A is used to set the gain of the amplifier. In this case, a ratio of 1:9 is used to create a gain of 10V/V, but many different gain configurations are possible. The second RES11A is used to build a high CMRR, low drift, unity gain difference amplifier. This design provides a precision, differential-to-single ended amplifier with very high input impedance. A smaller, lower power design, a two op amp instrumentation amplifier, is possible using the dual channel LMC6082 and only one RES11A matched pair at the expense of higher CMRR.