2-phase threshold detector based circuits
A switched capacitor circuit includes a threshold detector to generate a threshold detection signal when a difference between first and second input signals crosses a predetermined level. A coarse current source produces a coarse ramp. A series sampling capacitor samples a coarse output voltage when the threshold detector indicates a first threshold crossing. The sampling capacitor is connected in series with a fine current source producing a fine ramp.
1. A switched-capacitor circuit, comprising:
a threshold detector to generate a threshold detection signal when a difference between first and second input signals crosses a predetermined level;
a switched capacitor network coupled to the threshold detector;
a coarse current source coupled to the switched capacitor network, the coarse current source produces a coarse ramp;
a fine current source coupled to the switched capacitor network, the fine current source produces a fine ramp;
a series capacitor coupled to the fine current source; and
a series sampling switch coupled to the series capacitor and the threshold detector, the series sampling switch samples a coarse output voltage of the switched capacitor network when the threshold detector indicates first threshold crossing.
2. The switched-capacitor circuit as claimed in claim 1 , wherein the predetermined level is zero.
3. The switched-capacitor circuit as claimed in claim 1 , wherein the threshold detector is a zero-crossing detector.
4. The switched-capacitor circuit as claimed in claim 1 , wherein the threshold detector is a comparator.
5. The switched-capacitor circuit as claimed in claim 1 , wherein the threshold detection signal is adjustable.
6. The switched-capacitor circuit as claimed in claim 1 , wherein the threshold detector generates a dual threshold detection signal.
7. The switched-capacitor circuit as claimed in claim 1 , further including an output sampling capacitor and an output sampling switch, the output sampling switch turns OFF when the threshold detector indicates a second threshold crossing.
8. A differential switched-capacitor circuit, comprising:
a threshold detector to generate a threshold detection signal when a difference between first and second input signals crosses a predetermined level;
a switched capacitor network coupled to the threshold detector;
a coarse current source, coupled to the switched capacitor network, the coarse current source produces a coarse ramp;
a fine current source, coupled to the switched capacitor network, the fine current source produces a fine ramp;
a series capacitor coupled to the fine current source; and
a series sampling switch coupled to the series capacitor and the threshold detector, the series sampling switch samples a coarse output voltage of the switched capacitor network when the threshold detector indicates first threshold crossing.
9. The differential switched-capacitor circuit as claimed in claim 8 , wherein the predetermined level is zero.
10. The differential switched-capacitor circuit as claimed in claim 8 , wherein the threshold detector is a zero-crossing detector.
11. The differential switched-capacitor circuit as claimed in claim 8 , wherein the threshold detector is a comparator.
12. The differential switched-capacitor circuit as claimed in claim 8 , wherein the threshold detection signal is adjustable.
13. The differential switched-capacitor circuit as claimed in claim 8 , wherein the threshold detector generates a dual threshold detection signal.
14. The differential switched-capacitor circuit as claimed in claim 8 , further including an output sampling capacitor and an output sampling switch, the sampling switch turns OFF when the threshold detector indicates a second threshold crossing.
15. A method for reducing the effect of finite output resistance of a current source in a threshold detector based circuit, the method comprising:
charging a switched capacitor network with a coarse current source;
sampling a coarse output voltage of the switched capacitor network on a series capacitor when the threshold detector indicates a crossing of a predetermined threshold;
connecting the series capacitor in series with a fine current source; and
charging the switched capacitor network with the fine current source.
16. A method for reducing the effect of finite output resistance of a current source in a differential threshold detector based circuit, the method comprising:
charging a differential switched capacitor network with coarse current sources;
sampling a coarse output voltage of the switched capacitor network on a series capacitor when a threshold detector indicates a crossing of a predetermined threshold;
connecting the series capacitor in series with fine current sources; and
charging the switched capacitor network with the fine current sources.