DELTA-SIGMA MODULATORS USING FREQUENCY-MODULATED INTERMEDIATE VALUES

This paper describes a new first- and second-order delta-sigma modulat or concept where the first integrator is extracted and implemented by a frequency modulator with the modulating signal as the input, The res ult is a simple delta-sigma modulator with no need for digital-to-anal og converters, allowing straightforward multibit quantization. Without the frequency modulator, the circuit becomes a frequency-to-digital c onverter with delta-sigma noise shaping, An experimental first- and se cond-order modulator has been implemented in a 1.2-mu m standard digit al CMOS process and the results confirm the theory, For the first-orde r modulator an input signal amplitude of 150 mV resulted in a signal-t o-quantization noise ratio (SQNR) of approximate to 115 dB at 2 MHz sa mpling frequency and signal bandwidth of 500 Hz.