A 65nm CMOS DCXO system for generating 38.4MHz and a real time clock from a single crystal in 0.09mm2

Abstract

An integrated digitally-controlled crystal oscillator (DCXO) is presented that generates both 38.4 MHz and also a 32.768 kHz real time clock (RTC) from a single 38.4 MHz crystal. The DCXO can startup independently and transition seamlessly in and out of software control. The tuning range is 280 ppm with 2 ppb/step and guaranteed monotonicity. The phase noise is -135 dBc/Hz at 1kHz offset and -146 dBc/Hz at 10 kHz offset. The current consumption is 5 mA from a 1.4 V supply in full power mode and 234 μA in low power mode, including the LDO and all clock buffers. The DCXO is implemented in standard 65 nm digital CMOS with a die area of 0.09mm2.