Output hold circuits for sample-data circuits
A sampled-data analog circuit uses zero-crossing detector. A waveform generator produces a plurality of segments of ramp at the output. An output of a zero crossing detector controls a sampling switch, thereby causing a precise sample of the output voltage to be taken at the instant the zero crossing detector senses the zero crossing of the input signal. The waveform generator further includes a output hold function to maintain the output voltage.
1. A switched-capacitor circuit, comprising:
a level-crossing detector to generate a level-crossing detection signal when an input signal crosses a predetermined level; and
a waveform generator to generate a predetermined waveform;
said waveform generator including,
an amplifier operatively coupled to said level-crossing detector,
a current source operatively coupled to said amplifier, and
a capacitor operatively coupled to said amplifier;
said amplifier and said capacitor holding an output of said waveform generator in response to said level-crossing detection signal;
said waveform generator producing said predetermined waveform as a function of a current waveform generated by said current source.
2. The switched-capacitor circuit as claimed in claim 1 , wherein said level-crossing detector is a zero-crossing detector.
3. The switched-capacitor circuit as claimed in claim 1 , wherein said level-crossing detector is a comparator.
4. The switched-capacitor circuit as claimed in claim 1 , wherein said current source is a variable current source.
5. The switched-capacitor circuit as claimed in claim 4 , wherein said variable current source is turned OFF in response to said level-crossing detection signal.
6. The switched-capacitor circuit as claimed in claim 5 , wherein said level-crossing detector is a zero-crossing detector.
7. The switched-capacitor circuit as claimed in claim 5 , wherein said level-crossing detector is a comparator.
8. The switched-capacitor circuit as claimed in claim 1 , wherein said waveform generator produces a piecewise linear waveform.
9. The switched-capacitor circuit as claimed in claim 1 , wherein said amplifier includes a common-source device and an active load.
10. The switched-capacitor circuit as claimed in claim 1 , wherein said amplifier includes a source follower device.
11. The switched-capacitor circuit as claimed in claim 1 , wherein said current source is a variable current source, said waveform generator includes a switch, said switch being turned OFF in response to said level-crossing detection signal.
12. The switched-capacitor circuit as claimed in claim 11 , wherein said level-crossing detector is a zero-crossing detector.
13. The switched-capacitor circuit as claimed in claim 11 , wherein said level-crossing detector is a comparator.
14. A method for sampling a signal, the method comprising:
(a) sampling an input voltage using a switched capacitance network;
(b) determining when a node voltage of the switched capacitance network crosses a predetermined level;
(c) generating a predetermined waveform at an output node as a function of a current waveform generated by a current source;
(d) transferring the sampled input voltage to the output node; and
(e) holding the transferred sampled input voltage at a constant level at the output node when it is determined that the node voltage of the switched capacitance network crosses the predetermined level.
15. The method as claimed in claim 14 , wherein the pre-determined level is a zero voltage level.
16. The method as claimed in claim 14 , wherein the predetermined waveform is a piecewise linear waveform.
17. The method as claimed in claim 14 , wherein the predetermined waveform remains at a constant level when it is determined that the node voltage of the switched capacitance network crosses the predetermined level.
18. The method as claimed in claim 17 , wherein the pre-determined level is a zero voltage level.
19. The method as claimed in claim 14 , wherein the predetermined waveform is generated by a variable current source.