Implementation of a Ramp Generator with Schmitt Trigger Circuit for PWM Modulator Applications

A ramp (sawtooth wave) generator consisting of the voltage-current converter circuit, PMOS two-stage operational amplifier, current mirror and Schmitt trigger circuit is presented for the application of PWM modulator in this paper. The PWM modulator is one the PWM control core circuit of the switching power converters or the supply modulator of a wideband wireless transmitter. This paper proposes a ramp generator with Schmitt trigger circuit replace the conventional ramp circuit by use of two hysteresis comparators and one S-R latch circuit. The ramp generator with Schmitt trigger circuit can application to low power management integrated circuits, not only can reduce the area of the chip, more able to reduce the power consumption of the chip. This proposed ramp generator for PWM modulator circuit is design and implemented using the TSMC 0.35 mu m 2P4M process technology. Based on measured results, the chip size is 671.99 x 586 mu m(2) with power dissipation about 2.48 mW, and the chip supply voltage can from 1.9 V to 3.3 V. The ramp voltage which linearly rise from 0 V to 2.82 V, and the output frequency is about 500 KHz and 700 KHz stably when the chip supply voltage is fixed at 3.3 V and 2.0 V respectively.