Texas Instruments Incorporated
High Gain Detector Techniques for Low Bandwidth Low Noise Phase-Locked Loops

Abstract:

In described examples, a feedback loop has phase detection (PD) circuitry that has a reference input to receive a reference frequency signal, a feedback input to receive a feedback signal, and phase difference outputs. A phase to digital converter (P2DC) includes a first phase to charge converter (PCC) that has a gain polarity and a first phase error output; a second PCC that has an opposite gain polarity and a second phase error output. A differential loop filter has an amplifier with an inverting input coupled to the first phase error output and a non-inverting input coupled to the second phase error output. An analog to digital converter (ADC) has an input coupled to an output of the differential loop filter. A feedback path is coupled to the output of the P2DC, with an output of the feedback path providing the feedback signal to the PD feedback input.