Correlated double sampling circuit and sample hold circuit
View Patent ↗A correlated double sampling circuit has a sampling capacitor equally divided into a plurality of portions. In the correlated double sampling circuit, an input signal is sampled at a plurality of sampling points and an averaging switch is closed to obtain an average value of a plurality of sampling values obtained by sampling. High frequency noise superimposed on the input signal is thus reduced and a difference between the average values of the plurality of sampling values obtained by sampling is output.
1. A correlated double sampling circuit including a first input terminal, a second input terminal, a first output terminal, a second output terminal, a first feedback capacitor, a second feedback capacitor, a first sampling capacitor, a second sampling capacitor, and an operational amplifier, comprising:
the first sampling capacitor divided into a plurality of portions to sample a signal of a feed-through portion input to the first input terminal at a plurality of sampling points, the plurality of portions being connected in parallel with each other;
the second sampling capacitor divided into a plurality of portions to sample a signal of a data portion input to the second input terminal at a plurality of sampling points, the plurality of portions being connected in parallel with each other;
a plurality of sampling switches respectively connected in series with the plurality of portions of the first sampling capacitor;
a plurality of sampling switches respectively connected in series with the plurality of portions of the second sampling capacitor;
an averaging switch for calculating a first average value of a plurality of sampling values respectively obtained by sampling by the plurality of portions of the first sampling capacitor, and
an averaging switch for calculating a second average value of a plurality of sampling values respectively obtained by sampling by the plurality of portions of the second sampling capacitor, wherein
a difference between the first average value and the second average value is amplified using a value determined from a ratio of the first sampling capacitor, the second sampling capacitor, the first feedback capacitor, and the second feedback capacitor.
2. The correlated double sampling circuit according to claim 1 , further comprising a clock circuit for variably controlling a sampling frequency for sampling at the plurality of sampling points.
3. The correlated double sampling circuit according to claim 2 , further comprising:
a noise detection circuit for detecting a noise level of an output signal; and
a noise comparison circuit for holding the noise level detected by the noise detection circuit and comparing the detected noise level with a noise level detected at a preset clock timing, wherein
the clock circuit performs at least once a processing of adjusting a clocking timing to a clocking timing corresponding to a lowest one of the noise levels compared by the noise comparison circuit.
4. The correlated double sampling circuit according to claim 1 , wherein the averaging switch connects one terminal of one of the plurality of portions, which are divided, to one terminal of another of the plurality of portions.
5. A correlated double sampling circuit, including a first input terminal, a second input terminal, a first output terminal, a second output terminal, a first feedback capacitor, a second feedback capacitor, a first sampling capacitor, a second sampling capacitor, and an operational amplifier, comprising:
the first sampling capacitor equally divided into N portions to sample a signal of a feed-through portion input to the first input terminal at a plurality of sampling points (where N is an integer of at least 2), the N portions being connected in parallel with each other;
the second sampling capacitor equally divided into N portions to sample a signal of a data portion input to the second input terminal sampling at a plurality of sampling points (where N is an integer of at least 2), the N portions being connected in parallel with each other;
N sampling switches respectively connected in series with the N portions of the first sampling capacitor;
N sampling switches respectively connected in series with the N portions of the second sampling capacitor;
an averaging switch for calculating a first average value of a plurality of sampling values respectively obtained by sampling by the N portions of the first sampling capacitor;
an averaging switch for calculating a second average value of a plurality of sampling values respectively obtained by sampling by the N portions of the second sampling capacitor, wherein
a difference between the first average value and the second average value is amplified using a value determined from a ratio of the first sampling capacitor, the second sampling capacitor, the first feedback capacitor, and the second feedback capacitor.
6. The correlated double sampling circuit according to claim 5 , further comprising a clock circuit for variably controlling a sampling frequency for sampling at the plurality of sampling points.
7. The correlated double sampling circuit according to claim 5 , wherein the averaging switch connects one terminal of one of the N portions, which are equally divided, to one terminal of another of the N portions.