Profile: Instruments, Inc. manufactures and markets precision electronic test & measurement instruments and systems. Our product line includes switching amplifier, linear amplifier, L & M series, and other test equipment. Our L series amplifiers contain regulated power supplies, a Pre-Amplifier PWB, Output PWBs, and an output transformer system. The L series Output PWB is a current source. Up to 50 PWBs may be combined and still maintain proper sharing of current. Voltage feedback is used to create a voltage source or resistive source. Our pulse width modulation requires that the output transistors switch at 4 to 10 times the maximum signal frequency. Amplifiers using this technique and voltage feedback have 60 dB of dynamic range, and distortion of less than 0.2%. Current feedback can be used to synthesize a resistive output impedance. A PWM amplifier may be used to reproduce arbitrary waveforms. PWM amplifiers are full bridge output circuits that achieve a high degree of cancellation of the switching frequency harmonic sidebands. The harmonic sidebands (ripple) consist of odd harmonics of the input signal (fi) centered around even harmonics of the switching frequency (fs).