Circuit and method for dynamically adjusting a filter bandwidth
View Patent ↗A tracking circuit ( 100 ) is provided for controlling a locally-generated clock. A receive channel ( 110 ) in the tracking circuit receives an incoming signal and a local clock, generates a local signal based on the local clock, and compares the local signal and the incoming signal to generate a data signal and an unfiltered phase error signal. A loop filter ( 120 ) filters the unfiltered phase error signal to provide a filtered phase error signal. A numerically controlled oscillator ( 140 ) generates a correction clock based on the filtered phase error signal. And a filter control circuit ( 160 ) provides one or more filter control signals to control operational parameters of the loop filter. The correction clock is provided to the receive channel to modify at least one of the phase and frequency of the local clock. In addition, a sample switch ( 125 ) may also be provided to sample the unfiltered phase error signal.
1. A tracking circuit for controlling a locally-generated clock, comprising:
a receive channel for receiving an incoming signal and a local clock, generating a local signal based on the local clock, and comparing the local signal and the incoming signal to generate a data signal and an unfiltered phase error signal;
a loop filter for filtering the unfiltered phase error signal to provide a filtered phase error signal;
a numerically controlled oscillator for generating a correction clock based on the filtered phase error signal;
a filter control circuit for providing one or more filter control signals to control operational parameters of the loop filter; and
a sample switch located between the receive channel and the loop filter for sampling the unfiltered phase error signal according to a timing signal,
wherein the correction clock is provided to the receive channel to modify at least one of the phase and frequency of the local clock.
2. A tracking circuit for controlling a local clock, as recited in claim 1 , wherein the 1 oop filter is a type two filter.
3. A tracking circuit for controlling a local clock, as recited in claim 1 , wherein the loop fitter further comprises:
a first amplifier having a first gain value, for receiving the unfiltered phase error signal and providing a first amplified signal;
a second amplifier having a second gain value, for receiving the unfiltered phase error signal and providing a second amplified signal;
a first adder for adding the second amplified signal to a first delayed signal to provide an accumulated signal;
a delay circuit for delaying the accumulated signal to provide the first delayed signal; and
a second adder for adding the first amplified signal to the accumulated signal to provide the filtered phase error.
4. A tracking circuit for controlling a local clock, as recited in claim 3 , wherein the one or more filter control signals control the first and second gain values.
5. A tracking circuit for controlling a local clock, as recited in claim 1 , wherein the numerically-controlled oscillator further comprises:
an adder for adding the filtered phase error to a delayed signal to provide an intermediate signal;
a delay circuit for delaying the intermediate signal to provide the delayed signal; and
a memory circuit for generating the correction clock based on the intermediate signal.
6. A tracking circuit for controlling a local clock, as recited in claim 1 , wherein the incoming signal is an ultra wideband signal.
7. A tracking circuit for controlling a local clock, as recited in claim 1 , wherein the sample rate of the timing signal can be changed during a tracking operation.
8. A tracking circuit for controlling a local clock, as recited in claim 1 , wherein the tracking circuit is formed on an integrated circuit.
9. A tracking circuit for controlling a local clock, as recited in claim 1 , wherein filter control circuit controls the operational parameters of the loop filter such that the loop filter has a first bandwidth during a first time period and a second bandwidth during a second time period.
10. A method of controlling a local clock, as recited in claim 9 , wherein the first bandwidth is greater than the second bandwidth.
11. A tacking circuit for controlling a local clock, comprising:
a receive channel for receiving an incoming signal and a local clock, generating a local signal based on the local clock, and comparing the local signal and the incoming signal to generate a data signal and an unfiltered phase error signal;
a loop filter for filtering the unfiltered phase error signal to provide a filtered phase error signal;
a numerically controlled oscillator for generating a correction clock based on the filtered phase error signal;
a filter control circuit for providing one or more filter control signals to control operational parameters of the loop filter;
a first adder for adding the filtered phase error to a phase rate change signal to produce a first intermediate signal;
a second adder for adding the first intermediate signal to a delayed signal to provide a second intermediate signal;
a delay circuit for delaying the second intermediate signal to generate the delayed signal; and
a memory circuit for generating the correction clock based on the second intermediate signal,
wherein the correction clock is provided to the receive channel to modify at least one of the phase and frequency of the local clock.
12. A tracking circuit for controlling a local clock, as recited in claim 11 , wherein the correction clock is a complex clock.
13. A tracking circuit for controlling a local clock, as recited in claim 11 , wherein:
the memory circuit is a look-up table,
a range of allowable values for the second intermediate signal are set to correspond to phases between 0 and 2.pi. radians,
the memory circuit contains sine and cosine values for each of the range of allowable values for the second intermediate signal, and
the correction clock is generated as a complex clock based on sine and cosine values corresponding values of the second intermediate signal.
14. A method of controlling a local clock, comprising:
receiving an incoming signal;
generating a local signal based on a local clock;
comparing the local signal with the incoming signal to generate an unfiltered phase error signal;
sampling the unfiltered phase error signal at a sample rate to generate a sampled phase error signal;
filtering the sampled phase error signal through a loop filter to provide a filtered phase error signal;
generating a correction clock based on the filtered phase error signal; and
modifying at least one of the phase and frequency of the local clock based on the correction clock
wherein operational parameters of the loop filter are periodically modified to alter the bandwidth of the loop filter, and
wherein the sample rate is modified to alter the bandwidth of the loop filter.
15. A method of controlling a local clock, as recited in claim 14 , wherein the loop filter is a type 2 digital filter.
16. A method of controlling a local clock, as recited in claim 14 ,
wherein the loop filter comprises first and second amplifiers, having first and second gain values, respectively, and
wherein the operational parameters of the loop filter are modified by altering the first and second gain values.
17. A method of controlling a local dock, as recited in claim 14 , wherein the operational parameters of the loop filter are modified such that the loop filter has a first bandwidth during a first time period and a second bandwidth during a second time period.
18. A method of controlling a local clock, as recited in claim 17 , wherein the first bandwidth is greater than the second bandwidth.
19. A method of controlling a local clock, as recited in claim 14 , wherein the method is implemented in an ultra wideband device.
20. A method of controlling a local clock, as recited in claim 14 , wherein the method is implemented in an integrated circuit.