Instrumentation absolute value differential amplifier circuit and applications

A low-cost, low-precision biological-signal amplifier comprising:

• a) at least one signal electrode and at least one reference electrode, the at least one signal electrode referenced to the at least one reference electrode;
• b) a first buffer amplifier configured to produce a first buffered signal corresponding to a first signal electrode of the at least one signal electrode, said first buffered signal having lower impedance than a first source signal at the first signal electrode;
• c) a second buffer amplifier configured to produce a second buffered signal corresponding to a first reference electrode of the at least one reference electrode, said second buffered signal having lower impedance than a second source signal at the first reference electrode;
• d) a first differential gain amplifier configured to produce a first differential signal proportional to a difference between the first buffered signal and the second buffered signal;
• e) a second differential gain amplifier configured to produce a second differential signal proportional to a difference between the second buffered signal and the first buffered signal;
• and
• f) a mixing circuit configured to emit an output signal, wherein the output signal equals the first differential signal when the first differential signal is greater than the second differential signal;
• and the output signal equals the second differential signal when the second differential signal is greater than the first differential signal.