Correlated-double-sampling switched-capacitor gain stages, systems implementing the gain stages, and methods of their operation
View Patent ↗Embodiments of switched-capacitor gain stage circuits and methods of their operation are provided. The circuit includes an operational amplifier, parallel sampling capacitors, an offset storage capacitor coupled to an amplifier input, and multiple switches that are configurable to place the gain stage circuit in a sampling state, a gain state, and an output state. In the sampling state, the switches are configured so that a first charge component representing an input signal is stored on the sampling capacitors, and a second charge component representing an amplifier offset voltage is stored on the offset storage capacitor. In the gain state, the switches are configured so that a third charge component representing a finite gain of the amplifier is stored on the offset storage capacitor. In the output state, the switches are configured so that the first, second, and third charge components contribute to an output signal produced at the output node.
1. A switched-capacitor gain stage circuit having an input node and an output node, the circuit comprising:
an operational amplifier having a first amplifier input, a second amplifier input, and an amplifier output coupled to the output node;
a plurality of sampling capacitors arranged in parallel and selectively coupled between the input node and a central node;
an offset storage capacitor having a first terminal coupled to the first amplifier input; and
a switching configuration having multiple switches that are configurable to place the gain stage circuit in a sampling state, a gain state, and an output state, wherein,
in the sampling state, the multiple switches are configured so that a first charge component representing an input signal on the input node is stored on the sampling capacitors, and a second charge component representing an amplifier offset voltage is stored on the offset storage capacitor,
in the gain state, the multiple switches are configured so that a third charge component representing a finite gain of the amplifier is stored on the offset storage capacitor, and
in the output state, the multiple switches are configured so that the first, second, and third charge components contribute to an output signal produced at the output node.
2. The circuit of claim 1 , wherein contribution of the second charge component to the output signal causes cancellation of the amplifier offset voltage from the output signal, and contribution of the third charge component to the output signal results in a gain enhancement to the output signal.
3. The circuit of claim 1 , wherein:
in the gain state, a fourth charge component representing flicker noise is stored on the offset storage capacitor.
4. The circuit of claim 3 , wherein:
in the output state, the fourth charge component results in attenuation of the flicker noise in the output signal.
5. The circuit of claim 1 , wherein the multiple switches are configured, in the sampling state:
to connect first terminals of the plurality of sampling capacitors to the input node, and to connect second terminals of the plurality of sampling capacitors to a first ground reference,
to connect a second terminal of the offset storage capacitor to a second ground reference, and
to connect the amplifier output to the first amplifier input.
6. The circuit of claim 1 , wherein the multiple switches are configured, in the gain state:
to connect the second terminals of the plurality of sampling capacitors to the central node, to connect a first terminal of a first one of the plurality of sampling capacitors to a first ground reference, and to connect a first terminal of a second one of the plurality of sampling capacitors to the amplifier output, and
to connect the first terminal of the offset storage capacitor to the central node and to the first amplifier input, and to connect a second terminal of the offset storage capacitor to a second ground reference.
7. The circuit of claim 1 , wherein the multiple switches are configured, in the output state:
to connect the second terminals of the plurality of sampling capacitors to the central node, to connect a first terminal of a first one of the plurality of sampling capacitors to a ground reference, and to connect a first terminal of a second one of the plurality of sampling capacitors to the amplifier output, and
to connect the first terminal of the offset storage capacitor to the first amplifier input, and to connect a second terminal of the offset storage capacitor to the central node.
8. The circuit of claim 1 , wherein:
the plurality of storage capacitors comprises a first sampling capacitor and a second sampling capacitor; and
the multiple switches comprise
a first switch coupled between the first sampling capacitor and the input node,
a second switch coupled between the second sampling capacitor and the input node,
a third switch coupled between the offset storage capacitor and a central node,
a fourth switch coupled between the amplifier output and a first connection point between the first sampling capacitor and the first switch,
a fifth switch coupled between a first ground reference and a second connection point between the second sampling capacitor and the second switch,
a sixth switch coupled between a second ground reference and a third connection point between the offset storage capacitor and the third switch,
a seventh switch coupled between a third ground reference and the central node,
an eighth switch coupled between the central node and the first amplifier input, and
a ninth switch coupled between the amplifier output and the first amplifier input.
9. The circuit of claim 1 , wherein the multiple switches are configurable to place the gain stage circuit in the sampling state, the gain state, and the output state in response to a plurality of switch control signals.
10. An electronic system comprising:
a correlated-double-sampling switched-capacitor gain stage circuit having an input node, an output node, and a central node, the gain stage circuit including
an operational amplifier having a first amplifier input, a second amplifier input, and an amplifier output coupled to the output node;
a first capacitor that can be selectively coupled between the input node and the central node;
a second capacitor coupled in parallel with the first capacitor, and that can be selectively coupled between the input node and the central node;
a third capacitor coupled to the first amplifier input, and that can be selectively coupled to the central node; and
a switching configuration having multiple switches that are configurable to place the gain stage circuit in a first configuration, a second configuration, and a third configuration, wherein,
in the first configuration a first charge component representing an input signal on the input node is stored on the first and second capacitors, and a second charge component representing an amplifier offset voltage is stored on the third capacitor,
in the second configuration, a third charge component representing a finite gain of the amplifier is stored on the third capacitor, and
in the third configuration, the first, second, and third charge components contribute to an output signal produced at the output node.
11. The electronic system of claim 10 , wherein the multiple switches comprise:
a first switch coupled between the first capacitor and the input node,
a second switch coupled between the second capacitor and the input node,
a third switch coupled between the third capacitor and the central node,
a fourth switch coupled between the amplifier output and a first connection point between the first capacitor and the first switch,
a fifth switch coupled between a first ground reference and a second connection point between the second capacitor and the second switch,
a sixth switch coupled between a second ground reference and a third connection point between the third capacitor and the third switch,
a seventh switch coupled between a third ground reference and the central node,
an eighth switch coupled between the central node and the first amplifier input, and
a ninth switch coupled between the amplifier output and the first amplifier input.
12. The electronic system of claim 10 , further comprising:
a switch control circuit coupled to the gain stage circuit, and configured to provide switch control signals to the multiple switches to sequentially place the gain stage circuit in the first, second, and third configurations.
13. The electronic system of claim 10 , wherein the electronic system is an analog to digital converter, and the gain stage circuit is an input stage to the analog to digital converter.
14. The electronic system of claim 10 , wherein the electronic system is a system selected from a group consisting of a computer, a wired communication device, a wireless communication device, a cellular telephone, a radio, a radio frequency (RF) receiver, an RF transmitter, an appliance, a gaming system, a sensor interface, an electricity meter, a power meter, a video recording and display system, a vehicle braking unit, and an engine control unit.
15. A method for applying a gain to an input signal, the method performed in a switched-capacitor gain stage circuit having an input node, an output node, a first sampling capacitor, a second sampling capacitor, and an operational amplifier having a first amplifier input, a second amplifier input, and an amplifier output coupled to the output node, the method comprising the steps of:
first configuring multiple switches of the gain stage circuit in a first configuration in which a first charge component representing an input signal on the input node is stored on the first and second sampling capacitors, and a second charge component representing an amplifier offset voltage is stored on a third capacitor that has a first terminal coupled to the first amplifier input;
second configuring the multiple switches in a second configuration in which a third charge component representing a finite gain of the amplifier is stored on the third capacitor; and
third configuring the multiple switches in a third configuration in which the first, second, and third charge components contribute to an output signal produced at the output node.
16. The method of claim 15 , wherein configuring the multiple switches in the first configuration comprises:
connecting first terminals of the first and second sampling capacitors to the input node, wherein second terminals of the first and second sampling capacitors are connected to a central node;
connecting the central node to a first ground reference;
connecting a second terminal of the third capacitor to a second ground reference; and
connecting the amplifier output to the first amplifier input.
17. The method of claim 16 , wherein configuring the multiple switches in the second configuration comprises:
disconnecting the first terminals of the first and second capacitors from the input node;
disconnecting the amplifier output from the first amplifier input;
disconnecting the central node from the first ground reference;
connecting the first terminal of the first sampling capacitor to the amplifier output;
connecting the first terminal of the second sampling capacitor to a third ground reference; and
connecting the first terminal of the third capacitor to the central node.
18. The method of claim 17 , wherein configuring the multiple switches in the third configuration comprises:
disconnecting the first terminal of the third capacitor from the central node;
disconnecting the second terminal of the third capacitor from the second ground reference; and
connecting the second terminal of the third capacitor to the central node.
19. The method of claim 15 , further comprising:
repeatedly performing the first, second, and third configuring steps.
20. The method of claim 15 , further comprising:
receiving switch control signals that cause the multiple switches to be configured in the first, second, and third configurations.