A 30 GHz PLL with Automated Frequency Control Option for Robust Operation in Harsh Environments

This paper presents a fractional-N phase-locked loop (PLL) circuit which offers robust operation at harsh environments and ease of measurement in aging and radiation tests. The PLL includes an automated frequency calibration (AFC) block whose main objective is to monitor the effects of operating conditions on the voltage controlled oscillator (VCO) in a closed-loop operation. The PLL generates frequencies ranging from 29GHz to 34 GHz with a VCO that has two analog capacitive tuning nodes and 16 digitally controlled sub-bands. In the long-term operation, the AFC will compensate frequency shifts in the VCO by autonomous band selection. Also, during aging/radiation tests, the reference input frequency can be swept around 100MHz in a 15 MHz sweep bandwidth while the 4 control bits are written via the AFC circuit. So the whole frequency range can be monitored without disturbing the low gain, analog tuning of the VCO with the measurements performed on the quasi-DC control voltage. Since the measurement relies on the FM demodulation principle, the circuit conveniently eliminates RF signal measurement during test of PLLs in harsh environments.