Design of Voltage Controlled Oscillator Based Analog to Digital Converter Using Time to Digital Converter

This work presents a design and analyzes of performance of Voltage Controlled Oscillator based Analog-to-Digital converter (VCO based ADC) in the presence of the nonidealities such as jitter, nonlinearity, mismatch and the metastability of the D-flip-flop. A VCO based ADC involves two operations Voltage to Frequency conversion and Time to digital conversion. A Voltage Controlled Oscillator based Analog-to-Digital converter (VCO based ADC) also called as VCO based quantizer or Frequency Delta sigma Modulator (FDSM) is a time-based architecture with first order noise shaping ability that converts an analog input signal into digital output signal. The VCO converts the analog signal to phase domain by producing a continues output signal whose frequency is proportional to the average analog input signal. A counter, that follows the VCO, counts the edges from the outputs of the VCO on each sampling clock period. The counter values correspond to be a quantized estimate of the analog input signal. Due to the fact that the VCO produces a continues-phase output signal, quantization error of the previous sample affect that of the current sample. It is used in gamma ray cameras, sensor applications and ultra sonic applications. The advantage of the VCO based ADC is high Sampling rate, Resolution is high. In this proposed work Time to digital converter (TDC) is used instead of using counters. TDC is used for time Quantization in VCO based ADC. It was implemented using PSPICE.