Image capturing device
An image capturing device includes a pixel circuit, a programmable-gain amplifier, an analog-to-digital conversion circuit, and a control circuit. The pixel circuit outputs a photoreception signal. The programmable-gain amplifier amplifies the photoreception signal with a first gain. The analog-to-digital conversion circuit further amplifies the amplified signal that has been amplified by the programmable-gain amplifier, with a second gain by having a circuit configuration changeable by control, and digitally converts the resultant signal. The control circuit controls the analog-to-digital conversion circuit.
1. An image capturing device, comprising:
a pixel circuit to output a photoreception signal;
a programmable-gain amplifier to amplify the photoreception signal with a first gain;
an analog-to-digital conversion circuit to further amplify the amplified signal, which was amplified with the first gain by the programmable-gain amplifier, with a second gain to generate a further-amplifier signal, and digitally convert the further-amplified signal into a digital signal, the analog-to-digital conversion circuit having a circuit configuration that changes based on externally applied control signals; and
a control circuit to control the analog-to-digital conversion circuit to further amplify the amplified signal and digitally convert the further-amplified signal by transitioning the analog-to-digital conversion circuit through a sequence of phases having correspondingly different configurations, using the control signals.
2. The image capturing device according to claim 1 , wherein
the analog-to-digital conversion circuit is a cyclic analog-to-digital conversion circuit, and
the control circuit is configured to cause the amplified signal to be further amplified with the second gain by changing the circuit configuration of the analog-to-digital conversion circuit.
3. The image capturing device according to claim 2 , wherein the analog-to-digital conversion circuit includes:
a comparator to convert, to the digital signal, a signal voltage Vout(i) sampled based on the further-amplified signal;
a digital-to-analog conversion circuit to which the digital signal output from the comparator is fed back, and which outputs an analog signal voltage Vdac; and
a circuit to output, when the output from the digital-to-analog conversion circuit is controlled to be connected and input to the circuit, a signal satisfying the amplified signal voltage Vout(i+1)=2×Vout(i)−Vdac to the comparator, and
the control circuit is configured to fix the analog signal voltage Vdac of the digital-to-analog conversion circuit to a constant level, and control the output from the digital-to-analog conversion circuit to be connected and input to the circuit.
4. The image capturing device according to claim 3 , wherein the control circuit is configured to cause the comparator to repeatedly output a signal voltage Vout(i+1) satisfying Vout(i+1)=2×Vout(i)−Vdac by repeating, a plurality of times, the control of connection and input in a state where the analog signal voltage Vdac of the digital-to-analog conversion circuit is released from the fixed state.
5. The image capturing device according to claim 3 , wherein a bit output system used in analog-to-digital conversion in the analog-to-digital conversion circuit is based on a setting of determination criteria of the comparator.
6. The image capturing device according to claim 1 , wherein the programmable-gain amplifier is a capacitive-coupling type programmable-gain amplifier configured to perform offset correction.
7. The image capturing device according to claim 1 , wherein a range of input voltages to the analog-to-digital conversion circuit is set based on a reference voltage of the programmable-gain amplifier.
8. The image capturing device according to claim 1 , wherein the analog-to-digital conversion circuit performs analog-to-digital conversion of 1.5 bits per cycle.
9. The image capturing device according to claim 1 , wherein the analog-to-digital conversion circuit performs analog-to-digital conversion of 2.5 bits per cycle.
10. The image capturing device according to claim 1 , wherein the image capturing device is a CMOS line sensor.
11. The image capturing device of claim 1 , wherein the control circuit is further configured to control the analog-to-digital conversion circuit in accordance with the sequence of phases, which include a reset phase, a data input phase, a hold phase, and a sample phase.
12. The image capturing device of claim 1 , wherein the sequence of phases of the analog-to-digital conversion circuit further include a signal amplification phase and an amplified-signal input phase.