Disclosed herein are systems and methods for linearizing frequency chirp in a frequency-modulated continuous wave (FMCW) coherent LiDAR system. Exemplary methods can include generating a continuous wave laser signal having a frequency characteristic, in which the frequency characteristic can include a frequency chirp over a frequency band in at least one period; and receiving a signal based on the generated laser signal. The methods can further include mixing the received signal with a local oscillator signal, the local oscillator signal having the frequency characteristic; determining at least one beat frequency based on the mixed signal; sampling the mixed signal at a rate equal to at least two times the beat frequency; determining a correction signal based on the sampled signal; and applying the correction signal to the laser signal.

Disclosed herein are systems and methods for linearizing frequency chirp in a frequency-modulated continuous wave (FMCW) coherent LiDAR system. Exemplary methods can include generating a continuous wave laser signal having a frequency characteristic, in which the frequency characteristic can include a frequency chirp over a frequency band in at least one period; and receiving a signal based on the generated laser signal. The methods can further include mixing the received signal with a local oscillator signal, the local oscillator signal having the frequency characteristic; determining at least one beat frequency based on the mixed signal; sampling the mixed signal at a rate equal to at least two times the beat frequency; determining a correction signal based on the sampled signal; and applying the correction signal to the laser signal.

An oscillator includes a tunable resonant circuit having an inductance and a variable capacitance coupled between first and second nodes, and a set of capacitances selectively coupleable between the first and second nodes. An input control node receiving an input control signal is coupled to the variable capacitance and set of capacitances. The tunable resonant circuit is tunable based on the input control signal. A biasing circuit biases the tunable resonant circuit to generate a variable-frequency output signal between the first and second nodes. A voltage divider generates a set of different voltage thresholds, and a set of comparator circuits with hysteresis compares the input control signal to the set of different voltage thresholds to generate a set of control signals. The capacitances in the set of capacitances are selectively coupleable between the first and second nodes as a function of control signals in the set of control signals.

Disclosed herein is a tunable resonant circuit including an inductance directly electrically connected in series between first and second nodes, a variable capacitance directly electrically connected between the first and second nodes, and a set of switched capacitances coupled between the first and second nodes. The set of switched capacitances includes a plurality of capacitance units, each capacitance unit comprising a first capacitance for that capacitance unit directly electrically connected between the first node and a switch and a second capacitance for the capacitance unit directly electrically connected between the switch and the second node. Control circuitry is configured to receive an input control signal and connected to control the switches of the set of switched capacitances. A biasing circuit is directly electrically connected to the tunable resonance circuit at the first and second nodes.

In one form, a spread spectrum clock generator includes an oscillator and a digital modulator. The oscillator has a control input for setting an output frequency, and an output for providing a clock output signal. The digital modulator is responsive to the clock output signal to provide a control code to the control input of the oscillator as a periodic signal with a plurality of discrete steps, wherein the digital modulator provides said control code at each of said plurality of discrete steps for substantially a predetermined time.

A signal generating circuit includes a control voltage setting unit (CVSU) configured to set a control voltage for a chirp signal using voltage-frequency characteristics indicating characteristics of an output frequency versus voltage; a VCO configured to alter the frequency of its output signal by the control voltage; a quadrature demodulator configured to perform quadrature demodulation of the output signal of the VCO to generate an inphase signal and a quadrature signal orthogonal to each other; and a frequency detector configured to detect the frequency of the output signal of the VCO on the basis of the inphase signal and quadrature signal. The CVSU corrects the control voltage by using the voltage-frequency characteristics derived from relationships between the control voltage and the frequency of the output signal of the VCO. The VCO generates the chirp signal based on the control voltage corrected by the CVSU.

An oscillation circuit includes: a periodic signal generator which generates a periodic signal whose frequency varies; and a clock generator which generates a clock signal having a frequency commensurate with the frequency of the periodic signal.

In described examples, a frequency modulated continuous wave (FMCW) synthesizer includes a control engine, and a phase locked loop (PLL) including a frequency divider, a control voltage generator (CVG), and a voltage controlled oscillator (VCO). The frequency divider modifies a VCO output frequency based on a control input. The CVG generates a control voltage based on a frequency reference and the frequency divider output. The VCO outputs a FMCW output having the VCO output frequency in response to the control voltage. The control engine generates the control input so that the VCO output frequency: from a first time to a second time, is a first frequency; from the second time to a third time, changes at a first rate; from the third time to a fourth time, changes at a second rate different from the first rate; and from the fourth time to a fifth time, is a second frequency.

A system for a target image reconstruction includes a stepped frequency transmitter configured to emit a stepped frequency waveform having different constant frequencies at different periods of time and a modulator configured to modulate the stepped frequency waveform emitted at each period of time with a modulation signal to output a modulated stepped frequency waveform with an increased bandwidth. The system includes a transceiver configured to transmit the modulated stepped frequency waveform to a target and to accept reflection of the modulated stepped frequency waveform reflected from the target, a mixer to interfere the unmodulated stepped frequency waveform and the reflection of the modulated stepped frequency waveform to produce a beat signal of the interference of the unmodulated stepped frequency waveform with the reflection of the modulated stepped frequency waveform, and a signal processor to reconstruct an image of the target from the beat signal.

A system for a target image reconstruction includes a stepped frequency transmitter configured to emit a stepped frequency waveform having different constant frequencies at different periods of time and a modulator configured to modulate the stepped frequency waveform emitted at each period of time with a modulation signal to output a modulated stepped frequency waveform with an increased bandwidth. The system includes a transceiver configured to transmit the modulated stepped frequency waveform to a target and to accept reflection of the modulated stepped frequency waveform reflected from the target, a mixer to interfere the unmodulated stepped frequency waveform and the reflection of the modulated stepped frequency waveform to produce a beat signal of the interference of the unmodulated stepped frequency waveform with the reflection of the modulated stepped frequency waveform, and a signal processor to reconstruct an image of the target from the beat signal.