Signal-adaptive and time-dependent analog-to-digital conversion rate in a ranging receiver
An integrated circuit may include a ranging receiver that includes an analog-to-digital converter (ADC) having a time-variant sampling or data rate. Notably, the sampling rate may be increased when a return signal is detected by the ranging receiver. For example, the return signal may be detected using a matched filter (such as a correlation of the return signal and a target signal) and a comparator having a time-variant threshold. The time-variant threshold may be decreased as a function of time after a transmit signal is output in order to track the channel response, such as a decrease in the return signal amplitude for objects at larger ranges. Alternatively or additionally, the sampling rate may be increased based at least in part on a predefined function (such as a closed-form expression or a stepwise function, e.g., a stairstep function) after the transmit signal is output.
1 . An integrated circuit, comprising:
a ranging receiver configured to receive a return signal corresponding to a transmit signal, down convert the return signal, and equalize the down converted return signal, wherein the equalization comprises a proportional gain applied to the down converted return signal based at least in part on a frequency of the down converted return signal, and wherein a higher frequency has a higher gain; and
an analog-to-digital converter (ADC), with a time-variant sampling rate, configured to convert the return signal from an analog domain to a digital domain, resample an output, and adjust the time-variant sampling rate based at least in part on a correlation corresponding to the output.
2 . The integrated circuit of claim 1 , wherein the ranging receiver is configured to increase the sampling rate when the return signal is detected.
3 . The integrated circuit of claim 2 , wherein the ranging receiver is configured to detect the return signal using multiple symbols or pulses in the return signal.
4 . The integrated circuit of claim 1 , wherein the ranging receiver is configured to increase the sampling rate as a function of time after the transmit signal is output.
5 . The integrated circuit of claim 4 , wherein the sampling rate is increased based at least in part on a predefined function.
6 . The integrated circuit of claim 5 , wherein the predefined function comprises: a stepwise function, or a closed-form expression.
7 . The integrated circuit of claim 1 , wherein the ranging receiver comprises a comparator having a time-variant threshold; and
wherein the comparator is configured to selectively change the sampling rate based at least in part on a comparison of a detection signal corresponding to the return signal and the time-variant threshold.
8 . The integrated circuit of claim 7 , wherein the ranging receiver comprises a matched filter configured to determine the correlation of the return signal and a target signal, and to provide the detection signal.
9 . The integrated circuit of claim 7 , wherein the ranging receiver is configured to decrease the time-variant threshold as a function of time after the transmit signal is output.
10 . The integrated circuit of claim 9 , wherein the time-variant threshold is decreased based at least in part on a predefined function.
11 . The integrated circuit of claim 10 , wherein the predefined function comprises: a stepwise function, or a closed-form expression.
12 . The integrated circuit of claim 7 , wherein the comparator comprises hysteresis, and after the sampling rate is increased to a higher sampling rate, the comparator is configured to maintain the higher sampling rate for a time interval corresponding to the transmit signal.
13 . The integrated circuit of claim 1 , wherein the ranging receiver comprises a time-of-flight ranging receiver.
14 . The integrated circuit of claim 1 , wherein the integrated circuit comprises a transmitter configured to encode transmit signals using a set of unique codes over a time period;
wherein, during a given time interval in the time period, a given transmit signal is encoded using a given unique code that is different from the unique codes used in other time intervals in the time period; and
wherein the transmitter is configured to select a starting unique code in the set of unique codes for use in a first time interval in the time period based at least in part on a random value or a transmitter-specific value, and the unique codes in the set of unique codes that are used in subsequent time intervals in the time period are based at least in part on a predefined pattern.
15 . The integrated circuit of claim 14 , wherein the given unique code comprises a pulse-position modulation code.
16 . The integrated circuit of claim 14 , wherein the predefined pattern comprises a sequential wrap-around order in the set of unique codes.
17 . An electronic device, comprising:
a ranging receiver configured to receive a return signal corresponding to a transmit signal, down convert the return signal, and equalize the down converted return signal, wherein the equalization comprises a proportional gain applied to the down converted return signal based at least in part on a frequency of the down converted return signal, wherein a higher frequency has a higher gain; and wherein the ranging receiver is further configured to calibrate the ranging receiver based at least in part on the proportional gain, store the calibration as a calibration factor, and digitally correct the equalized down converted return signal; and
an analog-to-digital converter (ADC), with a time-variant sampling rate, configured to convert the return signal from an analog domain to a digital domain, resample an output, and adjust the time-variant sampling rate based at least in part on a correlation corresponding to the output.
18 . The electronic device of claim 17 , wherein the ranging receiver is configured to increase the sampling rate when the return signal is detected or to increase the sampling rate as a function of time after the transmit signal is output.
19 . A method for sampling a return signal, comprising:
by a ranging receiver:
receiving the return signal corresponding to a transmit signal;
converting, using a local oscillator, the return signal to a down converted return signal;
equalizing the down converted return signal based at least in part on a frequency of the down converted return signal;
calibrating the ranging receiver;
converting, using an analog-to-digital converter (ADC), the return signal from an analog domain to a digital domain, wherein the ADC has a time-variant sampling rate;
correcting the equalized down converted return signal in the digital domain; and
resampling an output, and adjusting the time-variant sampling rate based at least in part on a correlation corresponding to the output.
20 . The method of claim 19 , wherein the method comprises increasing the sampling rate when the return signal is detected or increasing the sampling rate as a function of time after the transmit signal is output.
21 . The integrated circuit of claim 1 , further configured to calibrate the ranging receiver based at least in part on the proportional gain, store the calibration as a calibration factor, and digitally correct the equalized down converted return signal.