Fast chirp synthesis via segmented frequency shifting
In an illustrative integrated circuit, a chirp generator provides a chirp signal having linearly-ramped chirp intervals, while a shift frequency generator provides a signal having a different shift frequency during each of multiple segments in each chirp interval. A modulator combines the signals to derive a segmented chirp signal having multiple linearly-ramped chirp segments in each chirp interval. The modulator may be a single sideband modulator to provide frequency up-shifted and frequency down-shifted chirp segments. The segmented chirp signal may be suppressed during resettling intervals of the original chirp signal.
1. An integrated circuit that comprises:
a chirp generator configured to provide a chirp signal having linearly-ramped chirp intervals;
a shift frequency generator configured to provide a shift frequency signal having a different shift frequency during each of multiple segments in each chirp interval; and
a modulator configured to derive a segmented chirp signal from a product of the chirp signal with the shift frequency signal, the segmented chirp signal having multiple linearly-ramped chirp segments in each chirp interval, wherein the multiple linearly-ramped chirp segments in the segmented chirp signal comprise a saw-tooth pattern.
2. The integrated circuit of claim 1 , wherein the multiple linearly-ramped chirp segments in each chirp interval have an equal duration, an equal frequency slope, and an equal start frequency.
3. The integrated circuit of claim 1 , wherein the shift frequency generator comprises:
multiple quadrature frequency dividers configured to each provide a shift frequency signal in quadrature, each quadrature frequency divider configured to provide a different shift frequency; and
a multiplexer arrangement configured to select from the shift frequency signals for each of the multiple chirp segments.
4. The integrated circuit of claim 1 , wherein the shift frequency generator comprises at least one quadrature frequency divider configured to provide the shift frequency signal in quadrature.
5. The integrated circuit of claim 4 , wherein the modulator is a single-sideband modulator configured to produce an up-shifted signal output and a down-shifted signal output for each shift frequency of the shift frequency signal.
6. The integrated circuit of claim 5 , further comprising a switch arrangement configured to select from the up-shifted and down-shifted signal outputs for each of the multiple chirp segments.
7. The integrated circuit of claim 6 , wherein outside of the chirp intervals the switch arrangement is configured to isolate the up-shifted and down-shifted signal outputs from a switch output.
8. The integrated circuit of claim 1 , wherein the chirp segments have equal duration, and wherein the different shift frequencies are integer multiples of a base frequency.
9. The integrated circuit of claim 1 , further comprising:
a transmitter configured to generate a transmit signal based on the segmented chirp signal;
a receiver configured to down-convert a receive signal using the segmented chirp signal; and
signal processing circuitry configured to derive target range-velocity information based on the receive signal.
10. The integrated circuit of claim 9 , wherein the segmented chirp signal omits chirp segments during settling intervals of the chirp signal, and wherein processing circuitry is configured to interpolate range-velocity information for the omitted chirp segments.
11. A method that comprises:
generating a chirp signal having linearly-ramped chirp intervals;
generating a shift frequency signal having a different shift frequency during each of multiple segments in each chirp interval; and
deriving a segmented chirp signal from a product of the chirp signal with the shift frequency signal, the segmented chirp signal having multiple linearly-ramped chirp segments in each chirp interval, wherein the multiple linearly-ramped chirp segments in the segmented chirp signal comprise a saw-tooth pattern.
12. The method of claim 11 , wherein the generating the shift frequency signal comprises includes:
using multiple quadrature frequency dividers that each provide a shift frequency signal in quadrature, each quadrature frequency divider providing a different shift frequency; and
select from the shift frequency signals for each of the multiple chirp segments.
13. The method of claim 11 , wherein the deriving uses a single-sideband modulator that produces an up-shifted signal output and a down-shifted signal output for each shift frequency of the shift frequency signal.
14. The method of claim 13 , wherein the deriving comprises selecting from the up-shifted and down-shifted signal outputs for each of the multiple chirp segments.
15. The method of claim 11 , wherein the chirp segments have equal duration, and wherein the different shift frequencies are integer multiples of a base frequency.
16. The method of claim 11 , further comprising:
generating a transmit signal based on the segmented chirp signal;
down-converting a receive signal using the segmented chirp signal; and
deriving target range-velocity information based on the receive signal.
17. The method of claim 16 , wherein the segmented chirp signal omits chirp segments during settling intervals of the chirp signal, and wherein the deriving target range-velocity information comprises interpolating range-velocity information for the omitted chirp segments.
18. A radar device that comprises:
a chirp generator configured to provide a chirp signal having linearly-ramped chirp intervals;
a shift frequency signal generator configured to provide a shift frequency signal having a different shift frequency during each of multiple segments in each chirp interval; and
a modulator configured to derive a segmented chirp signal from a product of the chirp signal with the shift frequency signal, the segmented chirp signal having multiple linearly-ramped chirp segments in each chirp interval, wherein the multiple linearly-ramped chirp segments in the segmented chirp signal comprise a saw-tooth pattern.
19. The radar device of claim 18 , wherein the multiple linearly-ramped chirp segments in each chirp interval have an equal duration, an equal frequency slope, and an equal start frequency.
20. The radar device of claim 18 , further comprising:
a transmitter configured to generate a transmit signal based on the segmented chirp signal;
a receiver configured to down-convert a receive signal using the segmented chirp signal; and
signal processing circuitry configured to derive target range-velocity information based on the receive signal.