Circuit and a method for sampling an analog signal

1 . A charge-based sampling circuit for sampling an analog input signal comprising: a capacitive means, a reset switch, and a sampling switch; the reset switch and the sampling switch being connected to a signal generator circuit configured to provide periodic reset and sampling control signals to the respective switches for controlling their operation;

wherein the respective periodic reset and sampling control signals have equal duty factors and signal periods, and a phase delay with respect to one another being less than the control signals' duty factor such that the reset control signal and the sampling control signal have an overlap phase, thereby forming a four-phase operation wherein

during a reset phase, the reset switch is closed such that the terminals of the capacitive means are shorted causing the capacitive means to discharge, and the sampling switch is open disconnecting the analog input signal from the capacitive means;

during the overlap phase the reset switch remains closed and the sampling switch is closed connecting the analog input signal to the capacitive means thereby, by the non-zero resistance of the reset switch, partly integrating the analog input signal onto the capacitive means by a pre-charge value depending on a slew rate of the control signals, wherein the overlap phase is subsequent to the reset phase;

during a subsequent integration phase, the reset switch is open and the sampling switch remains closed thereby integrating the analog input signal onto the capacitive means;

during a subsequent hold phase the sampling switch is open and the reset switch remains open such that an integrated charge on the capacitive means is held constant.

2 . The charge-based sampling circuit according to claim 1 , wherein the reset and sampling control signals have variable clock slew rates.

3 . The charge-based sampling circuit according to claim 2 , wherein the reset and sampling control signals have a square waveform, or, a sinusoidal waveform.

4 . The charge-based sampling circuit according to claim 1 , wherein duty factor of the reset and sampling control signals is one-half the control signals' period, and the phase delay is greater than zero and smaller than one half of the control signals' period.

5 . A time-interleaved charge-based sampling circuit comprising M charge-based sampling circuits according to claim 1 configured to provide M sampled signals in a time-interleaved manner.

6 . The time-interleaved charge-based sampling circuit according to claim 5 , wherein the M charge-based sampling circuits are configured to successively sample the analog input signal.

7 . The time-interleaved charge-based sampling circuit according to claim 5 , wherein the operation of the respective charge-based sampling circuits is delayed by 1/M of the control signals' period.

8 . The time-interleaved charge-based sampling circuit according to claim 5 , wherein the duration of the reset phase is 1/M of the control signal's period, and

wherein the duration of the overlap phase is one half of the control signal's period minus 1/M of the control signal's period.

9 . An analog-to-digital converter comprising a charge-based sampling circuit according to claim 1 or a time-interleaved charge-based sampling circuit configured to provide M sampled signals in a time-interleaved manner.

10 . A method for sampling an analog input signal by means of a charge-based sampling circuit comprising a capacitive means, a reset switch, and a sampling switch, the method comprising providing periodic reset and sampling control signals to the respective switches for controlling their operation;

wherein the respective periodic reset and sampling control signals have equal duty factors and signal periods, and a phase delay with respect to one another being less than the control signals' duty factor such that the reset control signal and the sampling control signal have an overlap phase; and

wherein the providing the reset and sampling control signals further comprises:

during a reset phase, closing the reset switch such that the terminals of the capacitive means are shorted causing the capacitive means to discharge, and keeping the sampling switch open thereby disconnecting the analog input signal from the capacitive means;

during the overlap phase keeping the reset switch closed and closing the sampling switch thereby connecting the analog input signal to the capacitive means and thereby, by the non-zero resistance of the reset switch, partly integrating the analog input signal onto the capacitive means by a pre-charge value depending on a slew rate of the control signals, wherein the overlap phase is subsequent to the reset phase;

during a subsequent integration phase, opening the reset switch and keeping the sampling switch closed thereby integrating the analog input signal onto the capacitive means; and

during a subsequent hold phase opening the sampling switch and keeping the reset switch open such that an integrated charge on the capacitive means is held constant.

11 . A method for sampling an analog input signal by means of a time-interleaved charge-based sampling circuit comprising M charge-based sampling circuits, the charge-based sampling circuits respectively comprising a capacitive means, a reset switch, and a sampling switch and being configured to sample the analog input signal to provide M sampled signals related to the analog input signal, the method comprising:

controlling the reset and sampling switch of the respective M charge-based sampling circuits by the method according to claim 10 .

12 . The method according to claim 11 further comprising controlling the reset and the sampling switches of the respective charge-based sampling circuits such that the operation of the respective charge-based sampling circuits is delayed by 1/M of the control signals' period.