Voltage time converter, analog digital converter, and electronic device

Abstract

The present invention provides a voltage time converter that shortens a conversion time.　A voltage time converter (10) comprises: a capacitor (101) to which an input voltage (a voltage of an input signal line Vin_p) is applied; a constant current circuit (111); an auxiliary constant current circuit (113); a time signal generation unit (131); and an auxiliary constant current circuit control unit (13). The constant current circuit (111) supplies a current to the capacitor (101) to change the voltage (Vc) of the capacitor (101). The auxiliary constant current circuit (113) supplies a current to the capacitor (101) to change the voltage (Vc) of the capacitor (101). The time signal generation unit (131) generates a time signal (a signal of an output signal line Vout_p) that represents a time (td) until the voltage (Vc) of the capacitor (101) changes to a prescribed first threshold voltage (Vref1). The auxiliary constant current circuit control unit (13) performs control to supply the current to the auxiliary constant current circuit (113) during a period which is included in the period (td) from the start of the supply of the current by the constant current circuit (111) to the change of the voltage (Vc) of the capacitor (101) to the first threshold voltage (Vref1).

Description

Voltage-time converter, analog-to-digital converter and electronic device

[0001] The present disclosure relates to a voltage-to-time converter, an analog-to-digital converter, and an electronic device.

[0002] A voltage-to-time converter converts an input voltage signal into a time signal. By combining this voltage-to-time converter with a time-to-digital converter, an analog-to-digital conversion circuit can be configured. For example, an analog-to-digital conversion circuit configured by combining a voltage-to-time conversion circuit and a time-to-digital conversion circuit has been proposed (see, for example, Patent Document 1).

[0003] This prior art analog-to-digital conversion circuit further includes a successive approximation type analog-to-digital conversion circuit that generates a digital signal of higher order bits and also generates a residual voltage between an analog input voltage and an analog signal voltage corresponding to the digital signal of higher order bits. The voltage-to-time converter and the time-to-digital converter generate a digital signal of lower order bits based on the residual voltage.

[0004] The voltage-time conversion circuit described above includes a capacitor, a constant current source, and a comparison circuit. The input voltage is sampled by the capacitor. The capacitor is discharged by a current from the constant current source. As a result, the voltage of the capacitor changes at a constant slope. The comparison circuit detects when the voltage of the capacitor reaches a predetermined potential (e.g., 0 V). The signal representing the detection result of the comparison circuit is a signal representing time according to the input voltage.

[0005] JP 2013-251700 A

[0006] However, in the above-mentioned conventional technology, when the input voltage is low, the current of the constant current source is reduced to slow down the change in the capacitor voltage in order to improve conversion accuracy, which results in a problem of longer conversion time.

[0007] Therefore, the present disclosure proposes a voltage-to-time converter that shortens the conversion time, and an analog-to-digital converter and electronic device that use the voltage-to-time converter.

[0008] The voltage-time converter according to the present disclosure includes a capacitor to which an input voltage is applied, a constant current circuit that supplies current to the capacitor to change the voltage of the capacitor, an auxiliary constant current circuit that supplies current to the capacitor to change the voltage of the capacitor, a time signal generating unit that generates a time signal representing the time until the voltage of the capacitor changes to a predetermined first threshold voltage, and an auxiliary constant current circuit control unit that controls the auxiliary constant current circuit to supply the current during a period included in the period from when the constant current circuit starts to supply the current until the voltage of the capacitor changes to the first threshold voltage.

[0009] FIG. 1 is a diagram illustrating a configuration example of a voltage-time converter according to a first embodiment of the present disclosure. FIG. 2 is a diagram illustrating an example of operation of a voltage-time converter according to the first embodiment of the present disclosure. FIG. 3 is a diagram illustrating an example of operation of a voltage-time converter according to the first embodiment of the present disclosure. FIG. 4 is a diagram illustrating an example of operation of a voltage-time converter according to the first embodiment of the present disclosure. FIG. 5 is a diagram illustrating an example of configuration of a voltage-time converter according to a second embodiment of the present disclosure. FIG. 6 is a diagram illustrating an example of configurations of an inverter gate and a NOR gate according to a second embodiment of the present disclosure. FIG. 7 is a diagram illustrating an example of configurations of an inverter gate and a NOR gate according to a second embodiment of the present disclosure. FIG. 8 is a diagram illustrating an example of configurations of an inverter gate and a NOR gate according to a second embodiment of the present disclosure. FIG. 9 is a diagram illustrating an example of configurations of a voltage-time converter according to a third embodiment of the present disclosure. FIG. 10 is a diagram illustrating an example of configurations of a voltage-time converter according to a fourth embodiment of the present disclosure. FIG. 11 is a diagram illustrating an example of configurations of an analog-digital converter according to an embodiment of the present disclosure. FIG. 12 is a diagram illustrating another example of configuration of an analog-digital converter according to an embodiment of the present disclosure. FIG. 13 is a diagram illustrating an example of configuration of an imaging device according to an embodiment of the present disclosure.

[0010] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. The description will be given in the following order. Note that in the following embodiments, the same components are designated by the same reference numerals, and redundant description will be omitted. 1. First embodiment 2. Second embodiment 3. Third embodiment 4. Fourth embodiment 5. Application example to an analog-to-digital converter 6. Application example to an imaging device

[0011] (1. First Embodiment) [Configuration of Voltage-Time Converter] FIG. 1 is a diagram illustrating a configuration example of a voltage-time converter according to a first embodiment of the present disclosure. The same figure is a circuit diagram illustrating a configuration example of a voltage-time converter 10. The voltage-time converter 10 in the same figure converts the voltages of the input signal lines Vin_p and Vin_n into time signals, respectively. The converted time signals are output to the output signal lines Vout_p and Vout_n. The voltage-time converter 10 can generate a time signal corresponding to the difference between the voltages of the input signal lines Vin_p and Vin_n. Note that the input signals of the input signal lines Vin_p and Vin_n can be DC or AC signals.

[0012] Voltage-time converter 10 includes first voltage-time converter 11, second voltage-time converter 12, and auxiliary constant current circuit control unit 13. Voltage-time converter 10 is also connected to a power supply line Vdd for supplying power.

[0013] The first voltage-time converter 11 converts an input voltage transmitted via an input signal line Vin_p into a time signal and outputs the time signal to an output signal line Vout_p. The first voltage-time converter 11 includes a first capacitor 101, a first constant current circuit 111, a first auxiliary constant current circuit 113, switches 121 to 123, and a first time signal generator 131. The switches 121 to 123 each include a control terminal to which a control signal is input. MOS transistors, for example, can be used for the switches 121 to 123. The first time signal generator 131 can be configured with a comparison circuit.

[0014] The input signal line Vin_p is connected to one end of the switch 121. The other end of the switch 121 is connected to one end of the switch 122, one end of the switch 123, the non-inverting input terminal of the first time signal generating unit 131, the signal line 15, and one end of the first capacitor 101. The other end of the first capacitor 101 is connected to a common GND line. The other end of the switch 122 is connected to a source terminal of the first constant current circuit 111. The sink terminal of the first constant current circuit 111 is connected to the power supply line Vdd. The other end of the switch 123 is connected to a source terminal of the first auxiliary constant current circuit 113. The sink terminal of the first auxiliary constant current circuit 113 is connected to the power supply line Vdd.

[0015] A first threshold voltage Vref1 is input to an inverting input terminal of the first time signal generation unit 131. An output terminal of the first time signal generation unit 131 is connected to an output signal line Vout_p. A control signal φ1 is input to a control terminal of the switch 121. A control signal φ2 is input to a control terminal of the switch 122. A signal on the signal line 17 is input to a control terminal of the switch 123.

[0016] The first capacitor 101 is a capacitor to which an input voltage from an input signal line Vin_p is applied. The input voltage applied to the first capacitor 101 is referred to as a first input voltage.

[0017] The switch 121 transmits the input voltage of the input signal line Vin_p to the first capacitor 101. When the switch 121 is in a conductive state, the first capacitor 101 is charged to the first input voltage. When the switch 121 is then in a non-conductive state, the voltage of the first capacitor 101 is maintained. The switch 121 is controlled by a control signal φ1.

[0018] The first constant current circuit 111 supplies a constant current to the first capacitor 101. The first constant current circuit 111 supplies the constant current via a switch 122. Due to the supply of this constant current, the voltage of the first capacitor 101 changes at a constant gradient.

[0019] The switch 122 transmits the current of the first constant current circuit 111 to the first capacitor 101. The switch 122 is controlled by a control signal φ2.

[0020] The first auxiliary constant current circuit 113 supplies a constant current to the first capacitor 101. This first auxiliary constant current circuit 113 supplies the constant current via a switch 123. The supply of this constant current causes the voltage of the first capacitor 101 to change at a constant slope. As will be described later, the current of the first auxiliary constant current circuit 113 is superimposed on the current of the first constant current circuit 111 and supplied to the first capacitor 101.

[0021] The switch 123 transmits the current of the first auxiliary constant current circuit 113 to the first capacitor 101. The switch 123 is controlled by a signal transmitted through a signal line 17.

[0022] The first time signal generating unit 131 generates a time signal that indicates the time until the voltage of the first capacitor 101 changes to the first threshold voltage Vref1. As described above, the first time signal generating unit 131 can be configured with a comparison circuit. In this case, the first time signal generating unit 131 can generate the time signal by comparing the voltage of the first capacitor 101 with the first threshold voltage Vref1. The time signal generated by the first time signal generating unit 131 is output to the output signal line Vout_p.

[0023] The second voltage-time converter 12 converts an input voltage transmitted via an input signal line Vin_n into a time signal and outputs the time signal to an output signal line Vout_n. The second voltage-time converter 12 includes a second capacitor 102, a second constant current circuit 112, a second auxiliary constant current circuit 114, switches 124 to 126, and a second time signal generator 132. The switches 124 to 126 include control terminals to which control signals are input. MOS transistors, for example, can be used for the switches 124 to 126. The second time signal generator 132 can be configured with a comparison circuit.

[0024] The input signal line Vin_n is connected to one end of a switch 124. The other end of the switch 124 is connected to one end of a switch 125, one end of a switch 126, a non-inverting input terminal of the second time signal generating unit 132, the signal line 16, and one end of the second capacitor 102. The other end of the second capacitor 102 is connected to a common GND line. The other end of the switch 125 is connected to a source terminal of the second constant current circuit 112. The sink terminal of the second constant current circuit 112 is connected to the power supply line Vdd. The other end of the switch 126 is connected to a source terminal of the second auxiliary constant current circuit 114. The sink terminal of the second auxiliary constant current circuit 114 is connected to the power supply line Vdd.

[0025] The first threshold voltage Vref1 is input to an inverting input terminal of the second time signal generation unit 132. The output terminal of the second time signal generation unit 132 is connected to the output signal line Vout_n. A control signal φ1 is input to a control terminal of the switch 124. A control signal φ2 is input to a control terminal of the switch 125. A signal on the signal line 17 is input to a control terminal of the switch 126.

[0026] The second capacitor 102 is a capacitor to which an input voltage from the input signal line Vin_n is applied. The input voltage applied to the second capacitor 102 is referred to as a second input voltage. The second capacitor 102 is configured to have the same capacitance as the first capacitor 101.

[0027] The switch 124 transmits the input voltage of the input signal line Vin_n to the second capacitor 102. When the switch 124 is in a conductive state, the second capacitor 102 is charged to the second input voltage. Thereafter, when the switch 124 is in a non-conductive state, the voltage of the second capacitor 102 is maintained. The switch 124 is controlled by a control signal φ1.

[0028] The second constant current circuit 112 supplies a constant current to the second capacitor 102. This second constant current circuit 112 supplies the constant current via a switch 125. Due to the supply of this constant current, the voltage of the second capacitor 102 changes at a constant slope. The second constant current circuit 112 supplies a current of the same value as that of the first constant current circuit 111.

[0029] The switch 125 transmits the current of the second constant current circuit 112 to the second capacitor 102. The switch 125 is controlled by a control signal φ2.

[0030] The second auxiliary constant current circuit 114 supplies a constant current to the second capacitor 102. This second auxiliary constant current circuit 114 supplies the constant current via a switch 126. The supply of this constant current causes the voltage of the second capacitor 102 to change at a constant slope. As will be described later, the current of the second auxiliary constant current circuit 114 is superimposed on the current of the second constant current circuit 112 and supplied to the second capacitor 102. The second auxiliary constant current circuit 114 supplies a current of the same value as that of the first auxiliary constant current circuit 113.

[0031] The switch 126 transmits the current of the second auxiliary constant current circuit 114 to the second capacitor 102. The switch 126 is controlled by a signal transmitted through a signal line 17.

[0032] The second time signal generating unit 132 generates a time signal that indicates the time until the voltage of the second capacitor 102 changes to the first threshold voltage Vref1. As described above, the second time signal generating unit 132 can be configured with a comparator. The time signal generated by the second time signal generating unit 132 is output to the output signal line Vout_n.

[0033] The auxiliary constant current circuit control unit 13 controls the first auxiliary constant current circuit 113 and the second auxiliary constant current circuit 114. The auxiliary constant current circuit control unit 13 generates a control signal for turning on the switches 123 and 126 during an auxiliary constant current supply period, during which the first auxiliary constant current circuit 113 and the second auxiliary constant current circuit 114 simultaneously supply current, and outputs the control signal via a signal line 17. Here, the auxiliary constant current supply period is a period included in the shortest period of either the period from the start of current supply in the first constant current circuit 111 to the time when the voltage across the first capacitor 101 changes to the first threshold voltage Vref1 or the period from the start of current supply in the second constant current circuit 112 to the time when the voltage across the second capacitor 102 changes to the first threshold voltage Vref1.

[0034] As will be described later, the first constant current circuit 111 and the second constant current circuit 112 start supplying current at the same time. The current supply from the first auxiliary constant current circuit 113 and the second auxiliary constant current circuit makes it possible to make the voltage changes of the first capacitor 101 and the second capacitor 102 steeper.

[0035] The auxiliary constant current circuit control unit 13 includes comparison circuits 133 and 134 and an AND gate 141. A three-input AND gate can be used as the AND gate 141. The inverting input terminal of the comparison circuit 133 is connected to a signal line 15. The inverting input terminal of the comparison circuit 134 is connected to a signal line 16. A second threshold voltage Vref2 is supplied to the non-inverting input terminal of the comparison circuit 133 and the non-inverting input terminal of the comparison circuit 134. The AND gate 141 receives the output signals of the comparison circuits 133 and 134, and a control signal EN. The output terminal of the AND gate 141 is connected to a signal line 17.

[0036] The comparator circuit 133 compares the voltage of the first capacitor 101 with a second threshold voltage Vref2 to generate a signal for stopping the supply of current from the first auxiliary constant current circuit 113 .

[0037] The comparator circuit 134 compares the voltage of the second capacitor 102 with a second threshold voltage Vref2 to generate a signal that causes the second auxiliary constant current circuit 114 to stop supplying current.

[0038] By the action of the AND gate 141, the earliest one of the output signals of the comparison circuit 133 and the comparison circuit 134 is input to the switch 123 and the switch 126 via the signal line 17. This simultaneously stops the current supply from the first auxiliary constant current circuit 113 and the second auxiliary constant current circuit 114. The control signal EN input to the AND gate 141 is a signal that permits the first auxiliary constant current circuit 113 etc. to supply current.

[0039] 2A and 2B are diagrams illustrating an example of the operation of the voltage-time converter according to the first embodiment of the present disclosure. 2A and 2B are timing diagrams illustrating an example of the operation of the first voltage-time converter 11 and the second voltage-time converter 12. 2A and 2B also illustrate, as a comparative example, an example in which the first auxiliary constant current circuit 113 and the second auxiliary constant current circuit 114 are not operated.

[0040] 2A and 2B, "φ1" represents the waveform of the control signal φ1. "φ2" represents the waveform of the control signal φ2. "Vc" represents the waveform of the voltages of the first capacitor 101 and the second capacitor 102. The solid line waveform of "Vc" represents the voltage (Vc1) of the first capacitor 101. The dotted line waveform of "Vc" represents the voltage (Vc2) of the second capacitor 102. The dashed dotted line represents the voltage of the first threshold voltage Vref1. "Vout_p" represents the waveform of the voltage of the output signal line Vout_p. "Vout_n" represents the waveform of the voltage of the output signal line Vout_n. When the control signals φ1 and φ2 are at H level, the switches 121 and the like are in a conductive state.

[0041] 2A shows an example in which the difference between the first input voltage and the second input voltage is relatively large. When the control signal φ1 transitions to the H level, the first input voltage is applied to the first capacitor 101, and the second input voltage is applied to the second capacitor 102.

[0042] Next, the control signal φ1 goes low, and the voltages of the first capacitor 101 and the second capacitor 102 are maintained. At this time, the control signal φ2 goes high, and a current from the first constant current circuit 111 is supplied to the first capacitor 101. This current flows in a direction that charges the first capacitor 101. Therefore, the voltage of the first capacitor 101 rises at a constant slope. Similarly, a current from the second constant current circuit 112 is supplied to the second capacitor 102, and the voltage of the second capacitor 102 rises at a constant slope.

[0043] When the voltage of the first capacitor 101 reaches the first threshold voltage Vref1, the output voltage of the first time signal generation unit 131 changes to an H level. The time from the rising edge of the control signal φ2 to the rising edge of the output voltage of the first time signal generation unit 131 is the conversion result of the first input voltage. The output signal of the first time signal generation unit 131 is output to the output signal line Vout_p as the time signal of the first voltage-to-time conversion unit 11.

[0044] Similarly, when the voltage of the second capacitor 102 reaches the first threshold voltage Vref1, the output voltage of the second time signal generation unit 132 changes to an H level. The time from the rising edge of the control signal φ2 to the rising edge of the output voltage of the second time signal generation unit 132 is the conversion result of the second input voltage. The output signal of the second time signal generation unit 132 is output to the output signal line Vout_n as the time signal of the second voltage-time conversion unit 12.

[0045] Furthermore, the time (Δt in FIG. 2A ) from the rising edge of the output signal of the first time signal generator 131 to the rising edge of the output signal of the second time signal generator 132 corresponds to the difference between the first input voltage and the second input voltage. This Δt corresponds to the full-scale input time difference of the voltage-to-time converter 10. Note that in the example of FIG. 2A , the difference between the first input voltage and the second input voltage is relatively large, so the change in voltage of the first capacitor 101 can be made relatively steep. As a result, the delay time td from the rising edge of the control signal φ2 to the generation of a time signal from the first time signal generator 131 or the like is relatively short.

[0046] 2B shows an example in which the difference between the first input voltage and the second input voltage is relatively small. When Δt is set to the same value as in FIG. 2A, i.e., when the full-scale input time difference is fixed, it is necessary to slow down the change in voltage of the first capacitor 101 and the second capacitor 102 in order to reduce errors during conversion. In this case, the supply currents of the first constant current circuit 111 and the second constant current circuit 112 must be reduced, or the capacitances of the first capacitor 101 and the second capacitor 102 must be increased. This results in a problem of a longer delay time td.

[0047] 3 is a diagram showing an example of the operation of the voltage-to-time converter according to the first embodiment of the present disclosure. Similar to FIGS. 2A and 2B, this figure is a timing diagram showing an example of the operation of the first voltage-to-time converter 11 and the second voltage-to-time converter 12. This figure shows an example of the operation of the first auxiliary constant current circuit 113 and the second auxiliary constant current circuit 114. In this figure, "EN" represents the waveform of the control signal EN. "AUX" represents the waveform of the signal transmitted by the signal line 17. The two-dot chain line represents the voltage of the second threshold voltage Vref2. The notations used in FIGS. 2A and 2B are otherwise the same.

[0048] The control signal EN changes to H level in synchronization with the rising edge of the control signal φ2, causing the signal on the signal line 17 to transition to H level, and the first auxiliary constant current circuit 113 and the second auxiliary constant current circuit 114 simultaneously start supplying current.

[0049] Thereafter, when the voltage (Vc1) of the first capacitor 101 reaches the second threshold voltage Vref2, the signal on the signal line 17 transitions to the L level, thereby simultaneously stopping the current supply from the first auxiliary constant current circuit 113 and the second auxiliary constant current circuit 114.

[0050] 2A, a time signal is output to the output signal line Vout_p and the output signal line Vout_n. The first auxiliary constant current circuit 113 and the second auxiliary constant current circuit 114 function to shorten the delay time td.

[0051] 3 show an example in which the operations of the first auxiliary constant current circuit 113 and the second auxiliary constant current circuit 114 are stopped. In this example, the delay time td (td' in FIG. 3) becomes longer, and the time required for voltage-time conversion becomes longer.

[0052] A method for reducing mismatches in time signals in the voltage-to-time converter 10 of the present disclosure will be described. Mismatch reduction can be achieved by trimming each component circuit. In the circuit of FIG. 1 , the first capacitor 101, the second capacitor 102, the first constant current circuit 111, the second constant current circuit 112, the first auxiliary constant current circuit 113, and the second auxiliary constant current circuit 114 are trimming points. The first time signal generator 131, the second time signal generator 132, the first threshold voltage Vref1, and the auxiliary constant current circuit controller 13 are also trimming points.

[0053] Trimming can be performed as follows: (1) When a mismatch occurs in the output time lag characteristics relative to the input voltage due to the currents of the first constant current circuit 111 and the second constant current circuit 112 or the capacitances of the first capacitor 101 and the second capacitor 102, the currents of the first constant current circuit 111 and the second constant current circuit 112 and the capacitances of the first capacitor 101 and the second capacitor 102 are trimmed. (2) When a mismatch occurs in the output time lag characteristics relative to the input voltage due to a mismatch in the currents of the first auxiliary constant current circuit 113 and the second auxiliary constant current circuit 114, the comparison circuits such as the first time signal generator 131, and the thresholds of the auxiliary constant current circuit controller 13, causing the auxiliary constant current circuit controller 13 to malfunction. The currents of the first auxiliary constant current circuit 113 and the second auxiliary constant current circuit 114 are trimmed. The auxiliary constant current circuit controller 13, etc., the first threshold voltage Vref1, and the second threshold voltage Vref2 are trimmed. As described above, the effect of mismatch can be reduced by performing trimming.

[0054] In this way, the voltage-time converter 10 of the first embodiment of the present disclosure can shorten the time required for voltage-time conversion by arranging the first auxiliary constant current circuit 113 and the second auxiliary constant current circuit 114.

[0055] (2. Second Embodiment) The voltage-to-time converter 10 of the first embodiment described above uses an auxiliary constant current circuit control unit 13 including a comparison circuit 133. In contrast, the voltage-to-time converter 10 of the second embodiment of the present disclosure differs from the first embodiment described above in that the auxiliary constant current circuit control unit 13 is simplified.

[0056] [Configuration of Voltage-Time Converter] Fig. 4 is a diagram showing a configuration example of a voltage-time converter according to a second embodiment of the present disclosure. Similar to Fig. 1, Fig. 4 is a circuit diagram showing a configuration example of a voltage-time converter 10. The voltage-time converter 10 in Fig. 4 differs from the voltage-time converter 10 in Fig. 1 in that it includes an auxiliary constant current circuit control unit 13 configured by a gate circuit.

[0057] The first voltage-time converter 11 in Fig. 4 is configured by a circuit of an inverting gate 142 and an inverting gate 143 connected in series. Similarly, the second voltage-time converter 12 in Fig. 4 is configured by a circuit of an inverting gate 144 and an inverting gate 145 connected in series.

[0058] 4 includes a NOR gate 148 and an AND gate 149. A two-input NOR gate can be used as the NOR gate 148. A two-input AND gate can be used as the AND gate 149.

[0059] The signal line 15 and the signal line 16 are connected to the inputs of the NOR gate 148. The output of the NOR gate 148 and the control signal EN are connected to the inputs of the AND gate 149. The output of the AND gate 149 is connected to the signal line 17.

[0060] [Configuration of NOR Gate and AND Gate] Figures 5A to 5C are diagrams showing configuration examples of an inverter gate and a NOR gate according to a second embodiment of the present disclosure. Figure 5A is a circuit diagram showing a configuration example of an inverter gate 142. As shown in Figure 5A, the inverter gate 142 and the like are configured by connecting a p-channel MOS transistor 201 and an n-channel MOS transistor 204 in series between a power supply line Vdd and a common GND line. Note that inverter gates 143 to 145 also have a similar configuration.

[0061] 5B is a circuit diagram showing an example of the configuration of the NOR gate 148. The NOR gate 148 includes p-channel MOS transistors 202 and 203 and n-channel MOS transistors 205 and 206. Of these, the p-channel MOS transistors 202 and 203 and the n-channel MOS transistor 206 are connected in series between the power supply line Vdd and a common GND line. Since the two p-channel MOS transistors are connected in series in this way, the output voltage is inverted at a threshold voltage lower than that of the inverting gate 142.

[0062] FIG. 5C shows the transfer characteristics of the inverter gate 142 and the NOR gate 148. The vertical axis of FIG. 5C represents the input voltage, and the horizontal axis represents the output voltage. The solid line graph in FIG. 5C represents the transfer characteristics of the inverter gate 142. The dotted line graph in FIG. 5C represents the transfer characteristics of the NOR gate 148. As shown in FIG. 5C, the threshold of the NOR gate 148 is a lower voltage than the threshold of the inverter gate 142. The threshold of the inverter gate 142 can be applied to a first threshold voltage Vref1. The threshold of the NOR gate 148 can be applied to a second threshold voltage Vref2.

[0063] The configuration of the voltage-time converter 10 other than that described above is the same as the configuration of the voltage-time converter 10 in the first embodiment of the present disclosure, and therefore description thereof will be omitted.

[0064] As described above, in the voltage-to-time converter 10 according to the second embodiment of the present disclosure, the threshold voltages of the inverter gates 142 and the NOR gate 148 correspond to the first threshold voltage Vref1 and the second threshold voltage Vref2, respectively. This allows the first time signal generator 131, the second time signal generator 132, and the comparator circuit 134 to be replaced with the inverter gate 142 and the NOR gate 148. This allows the voltage-to-time converter 10 to be simplified.

[0065] (3. Third Embodiment) The voltage-time converter 10 of the first embodiment described above supplies a sink current to the first capacitor 101, etc. In contrast, the voltage-time converter 10 of the third embodiment of the present disclosure differs from the first embodiment described above in that it supplies a source current to the first capacitor 101, etc.

[0066] [Configuration of Voltage-Time Converter] Fig. 6 is a diagram showing a configuration example of a voltage-time converter according to a third embodiment of the present disclosure. Similar to Fig. 1, Fig. 6 is a circuit diagram showing a configuration example of a voltage-time converter 10. The voltage-time converter 10 in Fig. 6 differs from the voltage-time converter 10 in Fig. 1 in the connection of the first constant current circuit 111, the second constant current circuit 112, the first auxiliary constant current circuit 113, and the second auxiliary constant current circuit 114.

[0067] The first voltage-time converter 11 in Fig. 6 is configured by a circuit of serially connected inverter gates 142, 143, and 146. Similarly, the second voltage-time converter 12 in Fig. 6 is configured by a circuit of serially connected inverter gates 144, 145, and 147.

[0068] The source terminal of the first constant current circuit 111 is connected to a common GND line. The sink terminal of the first constant current circuit 111 is connected to one end of a switch 122. The other end of the switch 122 is connected to one end of the first capacitor 101. The source terminal of the first auxiliary constant current circuit 113 is connected to a common GND line. The sink terminal of the first auxiliary constant current circuit 113 is connected to one end of a switch 123. The other end of the switch 123 is connected to one end of the first capacitor 101. The source terminal of the second constant current circuit 112 is connected to a common GND line. The sink terminal of the second constant current circuit 112 is connected to one end of a switch 125. The other end of the switch 125 is connected to one end of the second capacitor 102. The source terminal of the second auxiliary constant current circuit 114 is connected to a common GND line. The sink terminal of the second auxiliary constant current circuit 114 is connected to one end of a switch 126. The other end of the switch 126 is connected to one end of the second capacitor 102 .

[0069] As a result, the first capacitor 101 is supplied with sink currents from the first constant current circuit 111 and the first auxiliary constant current circuit 113. The second capacitor 102 is supplied with sink currents from the second constant current circuit 112 and the second auxiliary constant current circuit 114.

[0070] The auxiliary constant current circuit control unit 13 in Fig. 6 includes a NAND gate 150 and a NOR gate 151. A two-input NAND gate can be used as the NAND gate 150. A two-input NOR gate can be used as the NOR gate 151. Signal lines 15 and 16 are connected to the inputs of the NAND gate 150. An output of the NAND gate 150 and a control signal EN are connected to the inputs of the NOR gate 151. An output of the NOR gate 151 is connected to a signal line 17.

[0071] The configuration of the voltage-time converter 10 other than that described above is the same as the configuration of the voltage-time converter 10 in the first embodiment of the present disclosure, and therefore description thereof will be omitted.

[0072] (4. Fourth Embodiment) The voltage-time converter 10 of the first embodiment described above includes the first voltage-time converter 11 and the second voltage-time converter 12. In contrast, the voltage-time converter 10 of the fourth embodiment of the present disclosure differs from the first embodiment described above in that the second voltage-time converter 12 is omitted.

[0073] [Configuration of Voltage-Time Converter] Fig. 7 is a diagram showing a configuration example of a voltage-time converter according to a fourth embodiment of the present disclosure. Similar to Fig. 1, Fig. 7 is a circuit diagram showing a configuration example of a voltage-time converter 10. The voltage-time converter 10 in Fig. 7 differs from the voltage-time converter 10 in Fig. 1 in that it includes a first voltage-time conversion unit 11 and an auxiliary constant current circuit control unit 13.

[0074] The auxiliary constant current circuit control section 13 in FIG. 7 is composed of a comparison circuit 133 and a two-input AND gate 152 .

[0075] The configuration of the voltage-time converter 10 other than that described above is the same as the configuration of the voltage-time converter 10 in the first embodiment of the present disclosure, and therefore description thereof will be omitted.

[0076] In this way, the voltage-time converter 10 according to the fourth embodiment of the present disclosure can reduce the time required for voltage-time conversion when it includes one voltage-time conversion unit.

[0077] (5. Application to Analog-Digital Converter) The voltage-time converter 10 described above can be applied to an analog-digital converter.

[0078] 8 is a diagram illustrating an example configuration of an analog-to-digital converter according to an embodiment of the present disclosure. The figure is a block diagram illustrating an example configuration of an analog-to-digital converter 1. The analog-to-digital converter 1 includes a voltage-to-time converter 10 and a time-to-digital converter 20.

[0079] The voltage-to-time converter 10 in FIG. 8 converts a voltage corresponding to the difference between the input signal 1 and the input signal 2 into time, and outputs the converted time signal to the time-to-digital converter 20 .

[0080] The time-to-digital converter 20 converts the input time signal into a digital signal. The time-to-digital converter 20 converts the time signal output from the voltage-to-time converter 10 into a digital signal.

[0081] 9 is a diagram illustrating another exemplary configuration of an analog-digital converter according to an embodiment of the present disclosure. The figure is a block diagram illustrating another exemplary configuration of the analog-digital converter 1. The analog-digital converter 1 in the figure includes an analog-digital conversion unit 30, a voltage-time converter 10, and a time-digital converter 20.

[0082] The analog-to-digital conversion unit 30 performs successive approximation type analog-to-digital conversion. This analog-to-digital conversion unit 30 includes digital-to-analog converters 31 and 32, a comparison circuit 33, and logic circuits 34 and 35. In FIG. 9, "digital-to-analog conversion" is written as "DAC."

[0083] The digital-to-analog converter 31 generates an analog signal under the control of the logic circuit 34 and superimposes it on the input signal 1. The digital-to-analog converter 32 generates an analog signal under the control of the logic circuit 34 and superimposes it on the input signal 2. The comparison circuit 33 compares the difference between the input signals 1 and 2 with a predetermined value (e.g., 0 V) ​​and outputs the comparison result to the logic circuit 34. The logic circuit 35 generates a clock signal for the comparison circuit 33. The logic circuit 34 controls the entire analog-to-digital conversion unit 30.

[0084] The values ​​of input signal 1 and input signal 2 change due to the superposition of the output signals of digital-to-analog converters 31 and 32. Logic circuit 34 performs conversion by changing the outputs of digital-to-analog converters 31 and 32 until the difference between the values ​​of input signal 1 and input signal 2 reaches a predetermined value. Analog-to-digital conversion unit 30 outputs a residual voltage after conversion to voltage-to-time converter 10. This residual voltage is the voltage difference between the converted signal and the analog signals corresponding to input signal 1 and input signal 2.

[0085] The voltage-to-time converter 10 converts the residual voltage from the analog-to-digital converter 30 into a time signal and outputs it to the time-to-digital converter 20 .

[0086] In this way, by using the voltage-time converter 10 of the present disclosure in the analog-to-digital converter 1, the time required for analog-to-digital conversion can be reduced.

[0087] (6. Application Example to Imaging Device) The voltage-time converter 10 of the above-described embodiment can be applied to an imaging device.

[0088] 10 is a diagram illustrating an example configuration of an imaging device according to an embodiment of the present disclosure. The figure is a block diagram illustrating an example configuration of an imaging device 5. The imaging device 5 includes an image sensor 2, a digital-to-analog converter 3, an analog-to-digital converter 1, and a processor 4.

[0089] The image sensor 2 captures an image of a subject and generates image data, which is a digital signal.

[0090] The digital-to-analog converter 3 converts the image data into an analog signal and generates a PAM4 signal, which is a differential analog signal.

[0091] The analog-to-digital converter 1 receives the PAM4 signal from the digital-to-analog converter 3 and generates a digital signal.

[0092] The processor 4 processes the digital signal from the analog-to-digital converter 1. The processor 4 is an example of a "processing circuit" in the present disclosure. The imaging device 5 is an example of an "electronic device" in the present disclosure.

[0093] The voltage-to-time converter 10 of the present disclosure operates at high speed, and therefore can be applied to applications that handle high-speed, multi-level signals such as PAM4.

[0094] The effects described in this specification are merely examples and are not limiting, and other effects may also be present.

[0095] The present technology may also be configured as follows: (1) A voltage-to-time converter including: a capacitor to which an input voltage is applied; a constant current circuit that supplies a current to the capacitor to change the voltage of the capacitor; an auxiliary constant current circuit that supplies a current to the capacitor to change the voltage of the capacitor; a time signal generation unit that generates a time signal representing the time until the voltage of the capacitor changes to a predetermined first threshold voltage; and an auxiliary constant current circuit control unit that controls the auxiliary constant current circuit to supply the current during a period included in the period from when the constant current circuit starts to supply the current to when the voltage of the capacitor changes to the first threshold voltage. (2) The voltage-to-time converter according to (1), wherein the time signal generation unit generates the time signal by comparing the voltage of the capacitor with the first threshold voltage. (3) The voltage-to-time converter according to (1) or (2), wherein the auxiliary constant current circuit control unit includes a circuit that generates a signal to stop the supply of the current from the auxiliary constant current circuit by comparing the voltage of the capacitor with a predetermined second threshold.(4) A power supply circuit includes a first voltage-to-time converter including the capacitor to which a first input voltage is applied, the constant current circuit, the auxiliary constant current circuit, and the time signal generator; and a second voltage-to-time converter including the capacitor to which a second input voltage is applied, the constant current circuit, the auxiliary constant current circuit, and the time signal generator, wherein the constant current circuit of the second voltage-to-time converter starts supplying the current in synchronization with the constant current circuit of the first voltage-to-time converter, and the auxiliary constant current circuit of the second voltage-to-time converter starts supplying the current in synchronization with the auxiliary constant current circuit of the first voltage-to-time converter. The voltage-to-time converter according to any one of (1) to (3), wherein the auxiliary constant current circuit control unit controls the auxiliary constant current circuits of the first voltage-to-time converter and the second voltage-to-time converter to simultaneously supply currents during a period that is included in the shortest of a period from when the constant current circuit of the first voltage-to-time converter starts supplying the current until the voltage of the capacitor of the first voltage-to-time converter changes to the first threshold voltage and a period from when the constant current circuit of the second voltage-to-time converter starts supplying the current until the voltage of the capacitor of the second voltage-to-time converter changes to the first threshold voltage. (5) The voltage-to-time converter according to (4), wherein the auxiliary constant current circuit control unit controls the auxiliary constant current circuits of the first voltage-to-time converter and the second voltage-to-time converter to simultaneously supply currents during a period that is included in the shortest of a period from when the constant current circuit of the first voltage-to-time converter starts supplying the current until the voltage of the capacitor of the first voltage-to-time converter changes to the first threshold voltage.(6) An analog-to-digital converter comprising: a capacitor to which an input voltage is applied, a constant current circuit that supplies a current to the capacitor to change the voltage of the capacitor, an auxiliary constant current circuit that supplies a current to the capacitor to change the voltage of the capacitor, a time signal generation unit that generates a time signal representing the time until the voltage of the capacitor changes to a predetermined first threshold voltage, and an auxiliary constant current circuit control unit that controls the auxiliary constant current circuit to supply the current during a period included in a period from when the constant current circuit starts to supply the current until the voltage of the capacitor changes to the first threshold voltage, and a time-to-digital converter that converts the time signal into a digital value. (7) The analog-to-digital converter according to (6), further comprising an analog-to-digital conversion unit that converts an input signal into a digital signal and generates a residual voltage between the input signal and an analog signal corresponding to the digital signal, wherein the voltage-to-time converter generates the time signal using the residual voltage as the input voltage. (8) An electronic device having: a capacitor to which an input voltage is applied; a constant current circuit that supplies a current to the capacitor to change the voltage of the capacitor; an auxiliary constant current circuit that supplies a current to the capacitor to change the voltage of the capacitor; a time signal generation unit that generates a time signal representing the time until the voltage of the capacitor changes to a predetermined first threshold voltage; and an auxiliary constant current circuit control unit that controls the auxiliary constant current circuit to supply the current during a period included in the period from when the constant current circuit starts to supply the current until the voltage of the capacitor changes to the first threshold voltage; and a processing circuit that processes the time signal.

[0096] REFERENCE SIGNS LIST 1 Analog-to-digital converter 5 Imaging device 10 Voltage-to-time converter 11 First voltage-to-time conversion unit 12 Second voltage-to-time conversion unit 13 Auxiliary constant current circuit control unit 20 Time-to-digital converter 30 Analog-to-digital conversion unit 101 First capacitor 102 Second capacitor 111 First constant current circuit 112 Second constant current circuit 113 First auxiliary constant current circuit 114 Second auxiliary constant current circuit 121 to 126 Switch 131 First time signal generation unit 132 Second time signal generation unit 133, 134 Comparison circuit 141, 149, 152 AND gates 142 to 147 Inverting gates 148 NOR gate 150 NAND gate

Claims

1. A voltage-time converter comprising: a capacitor to which an input voltage is applied; a constant current circuit that supplies a current to the capacitor to change the voltage of the capacitor; an auxiliary constant current circuit that supplies a current to the capacitor to change the voltage of the capacitor; a time signal generation unit that generates a time signal representing the time until the voltage of the capacitor changes to a predetermined first threshold voltage; and an auxiliary constant current circuit control unit that controls to supply the current to the auxiliary constant current circuit during a period included in the period from the start of the supply of the current in the constant current circuit until the voltage of the capacitor changes to the first threshold voltage.

2. The voltage-time converter according to claim 1, wherein the time signal generation unit generates the time signal by comparing the voltage of the capacitor with the first threshold voltage.

3. The voltage-time converter according to claim 1, wherein the auxiliary constant current circuit control unit includes a circuit that generates a signal for stopping the supply of the current in the auxiliary constant current circuit by comparing the voltage of the capacitor with a predetermined second threshold.

4. A first voltage-time conversion unit including the capacitor to which a first input voltage is applied, the constant current circuit, the auxiliary constant current circuit, and the time signal generation unit; and a second voltage-time conversion unit including the capacitor to which a second input voltage is applied, the constant current circuit, the auxiliary constant current circuit, and the time signal generation unit, wherein the constant current circuit of the second voltage-time conversion unit starts supplying the current in synchronization with the constant current circuit of the first voltage-time conversion unit, the auxiliary constant current circuit of the second voltage-time conversion unit starts supplying the current in synchronization with the auxiliary constant current circuit of the first voltage-time conversion unit, and the auxiliary constant current circuit control unit controls to simultaneously supply the respective currents to the auxiliary constant current circuit of the first voltage-time conversion unit and the auxiliary constant current circuit of the second voltage-time conversion unit during a period included in the shortest period among the period from the start of the supply of the current in the constant current circuit of the first voltage-time conversion unit until the voltage of the capacitor of the first voltage-time conversion unit changes to the first threshold voltage and the period from the start of the supply of the current in the constant current circuit of the second voltage-time conversion unit until the voltage of the capacitor of the second voltage-time conversion unit changes to the first threshold voltage. The voltage-time converter according to claim 1.

5. The auxiliary constant current circuit control unit includes a circuit that generates a signal for stopping the supply of the current of each of the auxiliary constant current circuit of the first voltage-time conversion unit and the auxiliary constant current circuit of the second voltage-time conversion unit by comparing the voltage of the capacitor of the first voltage-time conversion unit and the voltage of the capacitor of the second voltage-time conversion unit with a predetermined second threshold value. The voltage-time converter according to claim 4.

6. A capacitor to which an input voltage is applied, a constant current circuit that supplies a current to the capacitor to change the voltage of the capacitor, an auxiliary constant current circuit that supplies a current to the capacitor to change the voltage of the capacitor, a time signal generation unit that generates a time signal representing the time until the voltage of the capacitor changes to a predetermined first threshold voltage, and an auxiliary constant current circuit control unit that controls the supply of the current to the auxiliary constant current circuit during a period included in the period from the start of the supply of the current in the constant current circuit until the voltage of the capacitor changes to the first threshold voltage. A voltage-time converter, and a time-to-digital converter that converts the time signal into a digital value. An analog-to-digital converter having 7. The analog-to-digital converter further includes an analog-to-digital conversion unit that converts an input signal into a digital signal and generates a residual voltage between the input signal and an analog signal corresponding to the digital signal. The voltage-time converter generates the time signal using the residual voltage as the input voltage. The analog-to-digital converter according to claim 6.

8. A capacitor to which an input voltage is applied, a constant current circuit that supplies a current to the capacitor to change the voltage of the capacitor, an auxiliary constant current circuit that supplies a current to the capacitor to change the voltage of the capacitor, a time signal generation unit that generates a time signal representing the time until the voltage of the capacitor changes to a predetermined first threshold voltage, and an auxiliary constant current circuit control unit that controls the supply of the current to the auxiliary constant current circuit during a period included in the period from the start of the supply of the current in the constant current circuit until the voltage of the capacitor changes to the first threshold voltage. A voltage-time converter, and a processing circuit that processes the time signal. An electronic device having

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