7.1.1 Modulator

An input amplifier (A1, as shown in Functional Block Diagram) integrates the difference between the input current (V_IN/200 kΩ) and a switched ±100-µA current source. This current source is implemented by a switchable 200-µA source and a fixed 100-µA current sink. To understand the basic operation of the modulator, assume that V_IN = 0 V. The integrator will ramp in one direction until the comparator threshold is exceeded. The comparator and sense amp will force the current source to switch; the resultant signal is a triangular waveform with a 50% duty cycle. The internal oscillator forces the current source to switch at 500 kHz. The resultant capacitor drive is a complementary duty-cycle modulation square wave