A sequentially-switched variable-gain operational amplifier

A means for changing the gain or time constant of operational amplifiers in a precribed sequence of sixteen steps is described. Four bistable multivibrators are used the outputs of which control balanced diode switches. The first stage multivibrator is triggerred from a pulse generator which also controls the resetting of integrators. The latter operation is achieved using a single triode valve in parallel with the integrating capacitor and an auxiliary input to the integrator. Switching at a frequency of 10 kc/s is readilly obtained but lower switching frequencies (say 10 to 100 c/s) are more reasonable in practice. It is estimated that at such frequencies the gain may be switched with an accurancy of 2%.