A programmable clock generator that uses noise shaping and its application in switched-capacitor filters

A comparison of noise-shaping clock generators for switched-capacitor filters

“…In [1], a sixth-order G(z) gave a simulated SSNR at the filter output that exceeds 70 dB for low input frequencies (f in < 0:1f s ) for a second-order BPF and a fifth-order LPF. (The noise in the simulated SSNR includes only the noise in the samples due to jitter; it does not include circuit noise.)…”

“…The quantization noise N [n], which is the difference between the quantizer input and output, is fed back to the input through filter G(z). The transfer function HT (z) from the quantization noise N [n] to the jitter [n] in the sampling clock is [1] …”

“…Measured results for two SCF's revealed that the signal-to-noise ratio (SNR) was limited by circuit noise sources (from the op amps and switched capacitors) rather than by sampling noise caused by the jitter in the sampling clock [1]. Based on these results, lower order noiseshaping clock generators that give lower signal-to-sampling-noise ratio (SSNR) and require less IC area are worth investigating.…”

“…If the sampling clock fsis realized by integer division of a high-frequency system clock f c , only widely spaced sampling frequencies can be generated. A programmable sampling-clock generator with noise shaping can generate a wide range of sampling frequencies with fine resolution, as described in [1]. The generated clock f s has nonuniformly spaced sampling edges that align with the edges of a fast system clock fc; such alignment helps to reduce coupling of switching noise from digital circuits into the SCF.…”

“…The generated clock f s has nonuniformly spaced sampling edges that align with the edges of a fast system clock fc; such alignment helps to reduce coupling of switching noise from digital circuits into the SCF. In [1], the jitter in the sampling edges was concentrated at high frequencies by a sixth-order noise-shaping loop. When such a sampling-clock generator was used to clock a bandpass SCF, the center frequency of the bandpass filter (BPF) was programmable with a resolution of 0.08%.…”