请教高手关于PLL里面sigma_delta modulator问题

hotraymanf

为什么modulator freq不能高过PFD freq? Quantization noise increase?

The D-S modulators for the fractional-N synthesizer may not use the decimation filter to

suppress the high-frequency noise in the digital domain since the PLL with integer-N

dividers does not allow an intermediate level between N and N + 1. Therefore, the clock

frequency of the oversampling modulator must be same as the phase detector frequency in

order to not increase the quantization noise.?????

hotraymanf

自己顶一个

twofishes

思考下，呵呵

xxwan

从PFD的角度看，sigma delta modulator控制分频N或N+1，分频后的该信号在 PFD处 跟 参考时钟信号 比较，如果频率不一样，就失去了比较的意义。