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, each of the signal electrodes referenced to one of the at least one reference electrodes;
• b. a first buffer amplifier to produce a first buffered signal corresponding to the first signal electrode, said first buffered signal having lower impedance than a first source signal at the first signal electrode;
• c. a second buffer amplifier to produce a second buffered signal corresponding to the reference electrode, said second buffered signal having lower impedance than a second source signal at the reference electrode;
• d. a first differential gain amplifier 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 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 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.