双极工艺用于立体声解调的线性锁相环的设计

Analysis of a Linear Phase-Locked Loop for Stereo Demodulation in Bipolar Process

设计了一种1.5μm双极工艺用于FM广播立体声解调的锁相环。锁相环中鉴相器由传统的吉尔伯特单元电路转变成上下对称的双开关电路,这样增加了鉴相灵敏度和鉴相范围。环路中增加了直流放大器单元,可很方便地通过调整其增益,来调整环路的阻尼系数,使环路在稳定性,锁定时间,噪声带宽方面做了很好的折中。从电路上实现了晶体压控振荡器的设计。锁相环路中的压控振荡器采用Q值很高的晶体做谐振网络,这样既可以保证窄带锁相环所具有的很高的Q值,也可以降低压控振荡器的相位噪声。

A PLL used for stereo demodulation in FM broadcasting was designed in 1.5 μm bipolar process. Compared with traditional Gilbert cell, the structure of the phase detector was changed into upper and lower symmetrical dual-switch circuit. Its sensitivity and phase-detect range were increased. A DC amplifier was added in the loop. By adjusting the gain of the amplifier, a trade-off between the loop＇s steady state, lock time and noise bandwidth was get. The circuit of the crystal VCO in the loop with a high-Q crystal that used for the resonator network of the VCO was designed. It can get a high Q value of the narrow-band phase-locked loop, and can reduce the VCO phase noise.