IN-SYSTEM METHOD FOR MEASUREMENT OF CLOCK RECOVERY AND OSCILLATOR DRIFT
Various embodiments relate to an in-system measurement of clock signals in a communications circuit. A circuit may include a central processing unit and at least one phase error counter (PEC) that uses a measurement clock to determine the accuracy of a target signal. In some embodiments, the PEC may include a counter that compares a clock signal produced by a reference oscillator with the signal of the measurement clock by generating an oscillator phase error based the measured difference during a target period. In some embodiments, the PEC may measure the performance of a clock recovery module by measuring a difference between a produced recovered clock signal and the measurement clock signal, which may be the clock recovery phase error between the two signals. The CPU may also use the measured phase errors to determine other values related to the target signal(s).
1 . An apparatus that measures internal clock performance, the apparatus comprising:
an interface that receives a measurement clock signal from a measurement clock;
a timing circuit comprising:
a reference oscillator, wherein the timing circuit uses the reference oscillator for timing operations; and
a first measurement circuit that measures an oscillator phase difference between a reference oscillator clock signal produced by the reference oscillator and the measurement clock signal.
2 . The apparatus of claim 1 , further comprising:
a clock recovery module in the timing circuit that receives timing packets and outputs a recovered clock; and
a second measurement circuit that measures a clock recovery phase difference between a recovered clock signal based on the recovered timing packets and the measurement clock signal.
3 . The apparatus of claim 1 , further comprising:
a clock recovery module in the timing circuit that receives timing packets and outputs a recovered clock, wherein the first measurement circuit further measures the clock recovery phase difference between a recovered clock signal based on the recovered timing packets and the measurement clock signal.
4 . The apparatus of claim 1 , wherein the first measurement circuit comprises:
a timer that produces a sampling rate that triggers at the beginning of a target period, wherein the target period is based on the measurement clock signal;
a counter that increases a target count by throughout the target period based on a frequency of a target signal; and
a subtractor that produces the oscillator phase difference by subtracting an estimated value from the target count, wherein the estimated value is equal to the ideal number of target signal cycles during the target period.
5 . The apparatus of claim 2 , wherein the second measurement circuit comprises:
a timer with a sampling rate that triggers at the beginning of a target period, wherein the target period is based on the measurement clock signal; and
a counter comprising:
a rate comparator that comprising an up-down counter that produces a count-up value or a count-down value based on the measurement clock signal and the recovered clock.
6 . The apparatus of claim 4 , wherein the target signal is the recovered clock signal.
7 . The apparatus of claim 4 , wherein the target signal is the oscillator clock signal.
8 . The apparatus of claim 1 , further comprising:
a central processing unit (CPU) that produces a performance value from the oscillator phase difference.
9 . The apparatus of claim 2 , further comprising:
a central processing unit (CPU) that produces a performance value from the clock recovery phase difference.
10 . The apparatus of claim 1 , further comprising:
a user interface (UI) that outputs the oscillator phase difference from the timing circuit to a user and receives user commands.
11 . A method to measure internal clock performance, the method comprising:
receiving, by a first measurement circuit in a communication circuit, a reference oscillator clock signal from a reference oscillator included in a timing circuit within the communications circuit;
receiving a measurement clock signal received through an interface from a measurement clock; and
measuring an oscillator phase difference between the reference oscillator signal and the measurement clock signal.
12 . The method of claim 11 , further comprising:
receiving timing packets;
producing, by a clock recovery module in the timing circuit, a recovered clock signal based on the recovered clock timing packets;
receiving, by a second measurement circuit in the communications circuit, the measurement clock signal;
receiving, by the second measurement circuit, the recovered clock signal; and
measuring, by the second measurement circuit, a clock recovery phase difference between the measurement clock signal and the recovered clock signal.
13 . The method of claim 11 , further comprising:
receiving timing packets;
producing, by a clock recovery module in the timing circuit, a recovered clock signal based on the recovered clock timing packets;
receiving, by the first measurement circuit, a measurement clock signal;
receiving, by the first measurement circuit, the recovered clock signal; and
measuring, by the first measurement circuit, a clock recovery phase difference between the measurement clock signal and the recovered clock signal.
14 . The method of claim 11 , wherein the first measurement circuit comprises:
a timer that produces a sampling rate that triggers at the beginning of a target period, wherein the target period is based on the measurement clock signal;
a counter that increases a target count by throughout the target period based on a frequency of a target signal; and
a subtractor that produces the oscillator phase difference by subtracting an estimated value from the target count, wherein the estimated value is equal to the ideal number of target signal cycles during the target period.
15 . The method of claim 12 , wherein the second measurement circuit comprises:
a timer with a sampling rate that triggers at the beginning of a target period, wherein the target period is based on the measurement clock signal; and
a counter comprising:
a rate comparator that comprising an up-down counter that produces a count-up value or a count-down value based on the measurement clock signal and the recovered timing packets.
16 . The method of claim 14 , wherein the target signal is the recovered clock signal.
17 . The method of claim 14 , wherein the target signal is the oscillator clock signal.
18 . The method of claim 11 , further comprising:
producing, by a central processing unit (CPU) in the communications circuit, a performance value from the oscillator phase difference.
19 . The method of claim 12 , further comprising:
producing, by a central processing unit (CPU) in the communications circuit, a performance value from the clock recovery phase difference.
20 . The method of claim 11 , further comprising:
outputting, from a user interface (UI) to a user, the oscillator phase difference from the timing circuit; and
receiving, by the UI from the user, at least one user command.