High-Frequency Oscillator with Spread Spectrum and Automatic Amplitude Control Loop

This paper presents the design of a 750 MHz oscillator in 0.4 μ m CMOS technology, equipped with a spread spectrum circuit for EMI reduction and an automatic gain control loop for the stabilization of the output signal's amplitude, which, according to the specification, must not drop below 0.9 V in any case. The spread spectrum circuit, based on a capacitive tank and a pseudorandom bits generator clocked at 15 MHz, is sized to produce a 30 MHz spread over the central frequency. The automatic gain control loop reduces variations in the output signal amplitude in response to variations in signal frequency, which also results in a reduction both in emissions and in current consumption. In nominal conditions at central frequency the differential signal amplitude is 1.40 V, the current consumption is 2.31 mA and the maximum variation of amplitude caused by the spread spectrum is limited to 2.9% of the central value. In the worst-case scenario over PVT and frequency variations, the amplitude is reduced to 1.01 V, still with a margin on the specification.