Patent ID: 9007105
Filing Date: 2015-04-14
Classification: H03L

Abstract:
1. A hitless-switching phase-locked loop (PLL), comprising: an oscillator with an output having an output signal with a first frequency, where the first frequency is controllable by a first control parameter; a first time-to-digital converter (TDC) with a first input coupled to a first reference clock input of the PLL, a second input coupled to the oscillator output, and an output register capable of holding a first measured phase value; a second TDC with a first input coupled to a second reference clock input of the PLL, a second input coupled to the oscillator output, and an output register capable of holding a second measured phase value; a system configured for: calculating a first desired phase value by integrating a first parameter indicating a first desired frequency multiplication factor; calculating a second desired phase value by integrating a second parameter indicating a second desired frequency multiplication factor; comparing the first measured phase value with the first desired phase value to obtain a first phase error signal; comparing the second measured phase value with the second desired phase value to obtain a second phase error signal; selecting the first phase error signal; filtering the first phase error signal to obtain the first control parameter; forwarding the first control parameter to the oscillator; monitoring if the second desired phase value closely matches the second measured phase value; in response to determining a difference between the second desired phase value and the second measured phase value, adjusting the second desired phase value to minimize an error from the second measured phase value; receiving a reference select signal, the reference select signal indicating that the second reference clock must be used for locking the PLL; deselecting the first phase error signal; selecting the second phase error signal; filtering the second phase error signal to obtain the first control parameter; and forwarding the first control parameter to the oscillator.