Da conversion circuit, imaging device, and electronic circuit

Abstract

The present invention suppresses variation in high-order bits and compensate nonlinearity of a DA conversion output while suppressing an increase in the number of cells due to high resolution of DA conversion.　This DA conversion circuit is provided with a binary code cell on a low-order bit side and a thermometer code cell on a high-order bit side, wherein the thermometer code cell is provided with a first thermometer code cell unit, a second thermometer code cell unit, a first power supply for supplying a first power supply voltage to the first thermometer code cell unit, and a second power supply for supplying a second power supply voltage to the second thermometer code cell unit.

Description

DA conversion circuit, imaging device, and electronic circuit

[0001] This technology relates to a DA conversion circuit, an imaging device, and an electronic circuit. More specifically, this technology relates to a DA conversion circuit, an imaging device, and an electronic circuit that use both binary code and thermometer code.

[0002] In digital-to-analog (DA) conversion circuits, there are techniques to adjust the power supply voltage of the unit cell to compensate for the nonlinearity of the DA conversion output. For example, in a DA converter that performs digital-to-analog conversion by summing currents from multiple constant current sources, a technique has been proposed to compensate for current changes due to temperature changes in the constant current source provided corresponding to the most significant bit (see, for example, Patent Document 1).

[0003] Japanese Patent Application Publication No. 7-147540

[0004] However, with the conventional techniques described above, it was difficult to suppress variations in the higher bits while compensating for the nonlinearity of the DA conversion output. On the other hand, if the DA conversion circuit is constructed using only thermometer code cells in order to suppress variations in the higher bits, there is a problem in that the number of cells increases exponentially as the resolution of the DA conversion is increased.

[0005] This technology was developed in light of these circumstances, and aims to suppress the increase in the number of cells associated with higher resolution DA conversion, suppress variations in the higher bits, and compensate for the nonlinearity of the DA conversion output.

[0006] This technology was developed to solve the aforementioned problems, and its first aspect is a DA conversion circuit comprising a binary code cell on the lower bit side and a thermometer code cell on the upper bit side, wherein the thermometer code cell comprises a first thermometer code cell unit, a second thermometer code cell unit, a first power supply that supplies a first power supply voltage to the first thermometer code cell unit, and a second power supply that supplies a second power supply voltage to the second thermometer code cell unit. This enables high-resolution DA conversion while suppressing the exponential increase of the thermometer code cell, and also compensates for the nonlinearity of the DA conversion output while suppressing variations in the upper bits based on the power supply voltage of the thermometer code cell.

[0007] Furthermore, in the first aspect, the binary code cell may be provided with a reference power supply that supplies a reference power supply voltage to the binary code cell unit. This results in the lower bits being converted using D / A conversion based on the reference power supply voltage.

[0008] Furthermore, in the first aspect, the first power supply voltage may be lower than the reference power supply voltage, and the second power supply voltage may be higher than the reference power supply voltage. This has the effect of improving the compensation for the nonlinearity of the DA conversion output in response to the input voltage.

[0009] Furthermore, in the first aspect, the first power supply and the second power supply may each be variable voltage power supplies. This results in the power supply voltage of the thermometer code cell being set so as to compensate for the nonlinearity of the DA conversion output.

[0010] Furthermore, in the first aspect, the first power supply voltage and the second power supply voltage may be adjusted with reference to the reference power supply voltage of the binary code cell. This enables DA conversion on the lower bit side via the binary code cell, while improving the compensation for the nonlinearity of the DA conversion output in response to the input voltage.

[0011] Furthermore, in the first aspect, when the thermometer code cell units included in the thermometer code cell are divided into multiple groups, the difference in the number of thermometer code cell units included in each group may be one or less. This results in an improvement in the compensation for the nonlinearity of the DA conversion output based on the power supply voltage of each group of thermometer code cells.

[0012] Furthermore, in the first aspect, the first thermometer code cell unit may be positioned on the upper and lower sides of the thermometer code cell, and the second thermometer code cell unit may be positioned on the middle side of the thermometer code cell. This results in improved compensation for the nonlinearity of the DA conversion output based on the output current from the thermometer code cell unit corresponding to the power supply voltage for each group of thermometer code cells.

[0013] Furthermore, in the first aspect, the thermometer code cell may include a third thermometer code cell unit and a third power supply that supplies a third power supply voltage to the third thermometer code cell unit. This has the effect of improving the accuracy of compensation for the nonlinearity of the DA conversion output in response to the input voltage.

[0014] Furthermore, in the first aspect, the third thermometer code cell unit may be positioned above and below the middle of the thermometer code cell. This results in improved accuracy of compensation for the nonlinearity of the DA conversion output based on the output current from the thermometer code cell unit corresponding to the power supply voltage for each group of thermometer code cells.

[0015] Furthermore, in the first aspect, the first and second power supply voltages may be set such that the maximum value of the absolute value of the INL (Integral Nonlinearity) of the DA conversion output is minimized. This results in the power supply voltage of the thermometer code cell being adjusted to compensate for the nonlinearity of the DA conversion output based on the detection result of the INL of the DA conversion output.

[0016] Furthermore, in the first aspect, the first and second power supply voltages may be set such that the amplitude of the third harmonic of the DA conversion output is minimized. This results in the power supply voltage of the thermometer code cell being adjusted to compensate for the nonlinearity of the DA conversion output based on the detection result of the third harmonic of the DA conversion output.

[0017] Furthermore, the second aspect is an imaging device comprising an imaging unit provided with a plurality of pixels, an AD conversion unit that digitizes the pixel signals based on the comparison result between the pixel signals read from the pixels and a reference signal, and a DA conversion circuit that generates the reference signal based on DA conversion, wherein the DA conversion circuit comprises a binary code cell on the lower bit side and a thermometer code cell on the upper bit side, and the thermometer code cell comprises a first thermometer code cell unit, a second thermometer code cell unit, a first power supply that supplies a first power supply voltage to the first thermometer code cell unit, and a second power supply that supplies a second power supply voltage to the second thermometer code cell unit. This results in an improvement in the linearity of the AD conversion of the pixel signals while suppressing an increase in the circuit size of the DA conversion circuit.

[0018] Furthermore, the third aspect is an electronic circuit comprising an analog circuit and a DA conversion circuit that generates an analog signal supplied to the analog circuit based on DA conversion, wherein the DA conversion circuit comprises a binary code cell on the lower bit side and a thermometer code cell on the upper bit side, and the thermometer code cell comprises a first thermometer code cell unit, a second thermometer code cell unit, a first power supply that supplies a first power supply voltage to the first thermometer code cell unit, and a second power supply that supplies a second power supply voltage to the second thermometer code cell unit. This has the effect of improving the linearity of the analog signal while suppressing an increase in the circuit size of the DA conversion circuit.

[0019] This is a block diagram showing an example configuration of a DA conversion circuit according to the first embodiment. This is a block diagram showing an example configuration of a code cell unit of a DA conversion circuit according to the first embodiment. This is a block diagram showing an example connection between a code cell unit and a power supply of a DA conversion circuit according to the first embodiment. This is a block diagram showing a specific example of a DA conversion circuit according to the first embodiment. This is a diagram showing an example of the relationship between the output voltage and INL before and after power supply voltage adjustment according to the first embodiment. This is a diagram showing an example of the relationship between the frequency and amplitude of the output voltage before and after power supply voltage adjustment according to the first embodiment. This is a diagram showing an example of the relationship between the digital input and the on / off state of the code cell unit according to the first embodiment. This is a block diagram showing an example connection between a code cell unit and a power supply of a DA conversion circuit according to the second embodiment. This is a block diagram showing an example connection between a code cell unit and a power supply of a DA conversion circuit according to the third embodiment. This is a block diagram showing an example configuration of a power supply voltage evaluation system of a DA conversion circuit according to the fourth embodiment. This is a flowchart showing the power supply voltage evaluation process of a DA conversion circuit according to the fourth embodiment. This is a block diagram showing an example configuration of a power supply voltage evaluation system of a DA conversion circuit according to the fifth embodiment. This is a flowchart showing the power supply voltage evaluation process of a DA conversion circuit according to the fifth embodiment. This is a block diagram showing an example configuration of a communication device to which a DA conversion circuit according to the sixth embodiment is applied. This is a block diagram showing an example configuration of an imaging device to which the DA conversion circuit according to the seventh embodiment is applied.

[0020] The following describes embodiments for implementing this technology. The description will proceed in the following order: 1. First Embodiment (An example in which a thermometer code cell unit is divided into three groups and the power supply voltage of each group is set) 2. Second Embodiment (An example in which seven thermometer code cell units are divided into three groups: one unit each on the upper and lower sides, and five units on the middle side, and the power supply voltage of each group is set) 3. Third Embodiment (An example in which a thermometer code cell unit is divided into five groups and the power supply voltage of each group is set) 4. Fourth Embodiment (An example in which the power supply voltage of each thermometer code cell unit is adjusted based on the INL of the DA conversion output) 5. Fifth Embodiment (An example in which the power supply voltage of each thermometer code cell unit is adjusted based on the amplitude of the third harmonic of the DA conversion output) 6. Sixth Embodiment (An example in which the DA conversion circuit is applied to a communication device) 7. Seventh Embodiment (An example in which the DA conversion circuit is applied to an imaging device)

[0021] <1. First Embodiment> Figure 1 is a block diagram showing an example of the configuration of a DA conversion circuit according to the first embodiment.

[0022] In the figure, this DA conversion circuit can constitute a segment-type DAC (Digital to Analog Converter). This DA conversion circuit includes a binary code cell BU and a thermometer code cell MU. The binary code cell BU is located on the lower bit side, and the thermometer code cell MU is located on the higher bit side. The binary code cell BU includes i (where i is a positive integer) thermometer code cell units US1 to USi. The thermometer code cell MU includes n-i (where n is an integer greater than or equal to 3) thermometer code cell units USi+1 to USn.

[0023] Each binary code cell unit US1 through USi receives the bit value b via buffers DV1 through DVi, respectively. １ from b i The following is input. Bit values ​​from b1 to b i A binary code is set there. Bit values ​​b are set to each thermometer code cell unit USi+1 to USn via buffers DVi+1 to DVn, respectively. i+1from b n is input. Bit value b i+1 to b n is set with a thermometer code. Outputs of each binary code cell unit US1 to USi and each thermometer code cell unit USi+1 to USn are connected to a resistor RL.

[0024] Each of the binary code cell units US1 to USi and each of the thermometer code cell units USi+1 to USn includes an inverter IV and a resistor R. The resistor R is connected to a subsequent stage of the inverter IV. The resistance value of the resistor R of each binary code cell unit US1 to USi increases at a ratio of 2 ｉ . The resistors R of each thermometer code cell unit USi+1 to USn are set to equal values to each other.

[0025] Each binary code cell unit US1 to USi outputs currents I1 to I i in accordance with bit values b1 to b i . Each thermometer code cell unit USi+1 to USn outputs currents I i+1 to I n in accordance with bit values b i+1 to I n . These currents I1 to I n flow through the resistor RL, and DA conversion is performed by generating an analog voltage VO across the resistor RL in accordance with bit values b1 to b ｎ .

[0026] Here, for example, when a 6-bit DAC is configured only with thermometer code cells MU, 64 thermometer code cell units are required. On the other hand, when a 6-bit DAC is configured as a segmented DAC, the number of unit cells can be reduced to at minimum 7 cells (four binary code cell units and three thermometer code cell units).

[0027] The thermometer code cell units USi+1 to USn are divided into a plurality of groups, and the power supply voltage of the thermometer code cell units USi+1 to USn is set for each group. Here, it is preferable that the difference in the number of the thermometer code cell units USi+1 to USn included in each group is within one.

[0028] Figure 2 is a block diagram showing an example configuration of a code cell unit of a DA conversion circuit according to the first embodiment. In the figure, each binary code cell unit US1 to USi and each thermometer code cell unit USi+1 to USn each comprises a cell unit US. The cell unit US comprises a PMOS transistor TP and an NMOS transistor TN. The PMOS transistor TP and the NMOS transistor TN are connected in series with each other. A resistor R is connected at the connection point of the PMOS transistor TP and the NMOS transistor TN. A bit value b is input to the gate of the PMOS transistor TP and the gate of the NMOS transistor TN. At this time, a current I flows through the value of resistor R according to the bit value b.

[0029] Figure 3 is a block diagram showing an example of the connection between the code cell unit and the power supply of the DA conversion circuit according to the first embodiment. In this figure, an example is shown in which the thermometer code cell MU is divided into three groups.

[0030] In the same figure, binary code cell BU is binary code cell unit B １ From B ｉ Includes. The thermometer code cell MU is the thermometer code cell unit T. １ From T ｋ , T' １ From T' ｊ , T” １ From T" ｍ It is divided into three groups, each containing (k, j, and m are positive integers). At this time, the thermometer code cell unit T １ From T ｋ It is located on the lower side of the thermometer code cell MU. Thermometer code cell unit T' １ From T' ｊ It is located on the middle side of the thermometer code cell MU. Thermometer code cell unit T” １ From T" ｍ It is located on the upper side of the thermometer code cell MU.

[0031] Here, if we set k + j + m = p, then the thermometer code cell unit T of the n-bit segment type DAC１ From T ｋ , T' １ From T' ｊ , T” １ From T" ｍ The number p of is preferably set such that it satisfies the following equation: (I LSB +2I LSB +...+2 i-1 I LSB ) + p × 2 i I LSB = (2 n -1)I LSB

[0032] For example, in a 6-bit segment type DAC, i=4 and p=3 may be used, or i=3 and p=7. In a 7-bit segment type DAC, i=5 and p=3 may be used, or i=4 and p=7.

[0033] Binary code cell unit B １ From B ｉ It is connected to the power supply VD. Thermometer cord cell unit T １ From T ｋ , T” １ From T" ｍ It is connected to power supply VD1. Thermometer cord cell unit T' １ From T' ｊ This is connected to power supply DVD2. Each power supply DVD, DVD1, and DVD2 may be a variable power supply or a fixed power supply.

[0034] Power supply DVD is for each binary code cell unit B １ From B ｉ The reference power supply voltage VDD is supplied to each thermometer code cell unit T. １ From T ｋ , T” １ From T" ｍ The power supply voltage VDD + ΔVDD1 is supplied to each thermometer code cell unit T'. Power supply VDD2 is supplied to each thermometer code cell unit T'. １ From T' ｊA power supply voltage VDD + ΔVDD2 is supplied to it. The power supply voltages VDD + ΔVDD1 and VDD + ΔVDD2 can be adjusted relative to the reference power supply voltage VDD so that the nonlinearity of the DA conversion output is compensated for. In this case, voltages ΔVDD1 and ΔVDD2 can be set to have opposite polarities to each other.

[0035] Here, it is preferable to adjust the power supply voltages VDD+ΔVDD1 and VDD+ΔVDD2 such that the change in output impedance is small before and after adjusting each power supply voltage VDD+ΔVDD1 and VDD+ΔVDD2. At this time, it is preferable to satisfy the condition (k+m)ΔVDD1+jΔVDD2 << VDD. In addition, in order to improve the compensation effect of the nonlinearity of the DA conversion output, it is preferable to set k, j, and m to be approximately the same while making ΔVDD2 approximately equal to -2ΔVDD1.

[0036] Figure 4 is a block diagram showing a specific example of a DA conversion circuit according to the first embodiment. In this figure, an example is shown in which a 7-bit segment type DAC is configured using 11 cells.

[0037] In the same figure, in this 7-bit segment type DAC, the binary code cell unit B １ From B ４ and thermometer code cell unit T １ From T ７ It includes: Binary code cell unit B １ From B ４ It is connected to the power supply DVD and the thermometer cord cell unit T １ T2, T6, T ７ It is connected to power supply VD1 and thermometer cord cell unit T ３ From T ５ This is connected to power supply DVD2. Here, in order to compensate for the nonlinearity of the DA conversion output, for example, the reference power supply voltage VDD of power supply DVD can be set to 800mV, the power supply voltage of power supply DVD1 to VDD-10mV, and the power supply voltage of power supply DVD2 to VDD+20mV.

[0038] Figure 5 shows an example of the relationship between the output voltage and INL before and after power supply voltage adjustment according to the first embodiment.

[0039] In the figure, in the 7-bit segment type DAC of Figure 4, INL11 before adjusting the power supply voltages of power supplies VD1 and VD2 changes to INL13 after adjusting the power supply voltages of power supplies VD1 and VD2, and the nonlinearity of the output voltage decreases. At this time, the maximum value P1 and minimum value P2 of INL11 decrease significantly. Furthermore, to further reduce the nonlinearity of the output voltage, it is preferable to increase the number of thermometer code cell units. For example, in a 7-bit segment type DAC, the improvement effect on the nonlinearity of the output voltage is smaller in INL12 when only 5 binary code cell units and 3 thermometer code cell units are used compared to INL13 when only 4 binary code cell units and 7 thermometer code cell units are used.

[0040] Figure 6 shows an example of the relationship between the frequency and amplitude of the output voltage before and after power supply voltage adjustment according to the first embodiment.

[0041] In the figure, when a 1.7 GHz sine wave is input, the frequency characteristic J1 of the 7-bit segment type DAC in Figure 4 before adjusting the power supply voltages VD1 and VD2 changes to frequency characteristic J3 after adjusting the power supply voltages VD1 and VD2, improving the effective resolution from 6.0 bits to 6.5 bits. In the 7-bit segment type DAC, the frequency characteristic when using only 5 binary code cell units and 3 thermometer code cell units is J2, and the improvement in effective resolution is smaller compared to when using only 4 binary code cell units and 7 thermometer code cell units.

[0042] Figure 7 shows an example of the relationship between the digital input and the on / off state of the code cell unit according to the first embodiment. This figure shows the relationship between the digital input and the on / off state of the code cell unit of the 7-bit segment type DAC in Figure 4. The figure also shows the output voltage V when the input signal is a (a = 1 - 127). ０ The nonlinear component of V na That's what I decided.

[0043] In the same figure, for example, when a = 17, R Ｌ V by ΔI n17 It will be canceled. However, R Ｌis the voltage drop across resistor RL. ΔI is the increment of current I in accordance with ΔVDD1.

[0044] - Here, when a=16, the output voltage V ０ is 16I LSB -R Ｌ ΔI+V n16 is obtained. When a=32, the output voltage V ０ is 16I LSB -2R Ｌ ΔI+V n16 is obtained. When a=48, the output voltage V ０ is 48I LSB +V n48 is obtained. Therefore, as shown in FIG. 5, INL has a step every time the input signal a increases by 16.

[0045] As described above, in the above-mentioned first embodiment, the thermometer code cell units of the segmented DAC are divided into a plurality of groups, and the power supply voltage of the thermometer code cell unit of each group is adjusted. This enables higher resolution DA conversion while suppressing exponential increase of thermometer code cells, and can compensate for non-linearity of the DA conversion output while suppressing variation in upper bits based on the power supply voltage of the thermometer code cells.

[0046] <2. Second Embodiment> In the above-mentioned first embodiment, seven thermometer code cell units are divided into three groups, with two groups on the upper side and two on the lower side, and three groups in the middle, and power supply voltages for each group are set. In this second embodiment, seven thermometer code cell units are divided into three groups, with one group on the upper side and one on the lower side, and five groups in the middle, and power supply voltages for each group are set.

[0047] FIG. 8 is a block diagram showing an example of connection between a code cell unit of a DA conversion circuit and a power supply according to the second embodiment.

[0048] In this figure, this segmented DAC, similar to the segmented DAC in FIG. 4, includes binary code cell units B １ to B ４ and thermometer code cell units T １ to T ７comprising. Here, in this segmented DAC, the binary code cell unit B １ to B ４ are connected to a power supply VD, the thermometer code cell unit T １ , T ７ are connected to a power supply VD1, and the thermometer code cell units T2 to T6 are connected to a power supply VD2.

[0049] As described above, in the second embodiment described above, the seven thermometer code cell units are divided into three groups, with one on the upper side, one on the lower side, and five on the middle side, and the power supply voltage of each group is set. This makes it possible to compensate for the nonlinearity of the DA conversion output based on the power supply voltage of each group of thermometer code cells arranged on the lower bit side.

[0050] <3. Third Embodiment> In the first embodiment described above, the thermometer code cell units of the segmented DAC are divided into three groups, and the power supply voltage of the thermometer code cell units of each group is adjusted. In this third embodiment, the thermometer code cell units of the segmented DAC are divided into five groups, and the power supply voltage of the thermometer code cell units of each group is adjusted.

[0051] FIG. 9 is a block diagram showing an example of connection between code cell units and a power supply of a DA conversion circuit according to the third embodiment.

[0052] In the figure, this segmented DAC is obtained by adding thermometer code cell units T''' １ to T''' x , T'''' １ to T'''' y (where x and y are each a positive integer) and a power supply VD3 to the segmented DAC of FIG. 3. At this time, the thermometer code cells of this segmented DAC include thermometer code cell units T １ to T ｋ , T''' １ to T''' x , T' １ to T' ｊ , T'''' １ to T'''' y , T'' １ to T'' ｍIt is divided into five groups, each containing one of the following:

[0053] Thermometer code cell unit T"' １ From T"' x It is positioned in the lower middle section. Thermometer code cell unit T"" １ From T"" y It is positioned in the upper middle section. Thermometer code cell unit T"' １ From T"' x , T"" １ From T"" y It is connected to power supply DVD3. Power supply DVD3 may be a variable power supply or a fixed power supply. Power supply DVD3 is connected to each thermometer code cell unit T"' １ From T"' x , T"" １ From T"" y A power supply voltage VDD + ΔVDD3 is supplied to it. At this time, the power supply voltages VDD + ΔVDD1, VDD + ΔVDD2, and VDD + ΔVDD3 can be adjusted with reference to the reference power supply voltage VDD so that the nonlinearity of the DA conversion output is compensated for.

[0054] Here, it is preferable to adjust the power supply voltages VDD+ΔVDD1, VDD+ΔVDD2, and VDD+ΔVDD3 such that the change in output impedance is small before and after adjusting each power supply voltage VDD+ΔVDD1, VDD+ΔVDD2, and VDD+ΔVDD3. In this case, it is preferable to satisfy the condition (k+m)ΔVDD1+jΔVDD2+(x+y)ΔVDD3 << VDD.

[0055] Thus, in the third embodiment described above, the thermometer code cell unit of the segment-type DAC is divided into five groups, and the power supply voltage of the thermometer code cell unit in each group is adjusted. This makes it possible to achieve high resolution DA conversion while suppressing the exponential increase of the thermometer code cell, and also improves the compensation accuracy for the nonlinearity of the DA conversion output while suppressing variations in the higher bits based on the power supply voltage of the thermometer code cell.

[0056] In the above-described embodiment, a segment-type DAC in which the resolution bit depth, the number of thermometer code cell groups, and the number of unit cells are set to specific values ​​was used as an example. However, the present invention is applicable to segment-type DACs with any resolution bit depth, number of thermometer code cell groups, and number of unit cells.

[0057] <4. Fourth Embodiment> In the first embodiment described above, the thermometer code cell unit of the segment-type DAC was divided into multiple groups, and the power supply voltage of each group was set. In this fourth embodiment, the power supply voltage of the thermometer code cell unit of the segment-type DAC is adjusted based on the INL of the DA conversion output.

[0058] Figure 10 is a block diagram showing an example configuration of the power supply voltage evaluation system of a DA conversion circuit according to the fourth embodiment.

[0059] In the figure, this power supply voltage evaluation system adjusts the power supply voltage of the thermometer code cell unit of the segment type DAC 202 based on the INL of the DA conversion output. This power supply voltage evaluation system comprises an input unit 201, a segment type DAC 202, an INL evaluation unit 203, and a power supply voltage supply unit 204.

[0060] The input unit 201 inputs a slope wave digital signal to the segment type DAC 202. The input unit 201 is connected to the preceding stage of the segment type DAC 202.

[0061] In the segment-type DAC 202, the power supply voltage is set for each group of thermometer code cell units. The segment-type DAC 202 may be any of the segment-type DACs described in the first to third embodiments above.

[0062] The INL evaluation unit 203 detects and evaluates the INL of the segment-type DAC 202 based on the analog output of the segment-type DAC 202. At this time, the INL evaluation unit 203 may evaluate the maximum value of the absolute value of the INL of the segment-type DAC 202.

[0063] Based on the INL evaluation results from the INL evaluation unit 203, the power supply voltage supply unit 204 adjusts the power supply voltage of the thermometer code cell units of the segment type DAC 202 for each group and supplies it to the thermometer code cell units of the segment type DAC 202.

[0064] Figure 11 is a flowchart showing the power supply voltage evaluation process of a DA conversion circuit according to the fourth embodiment.

[0065] In the figure, the input unit 201 inputs the slope wave digital signal to the segment type DAC 202 (S101).

[0066] Next, the segment-type DAC 202 performs D / A conversion on the digital signal input from the input unit 201 and outputs an analog waveform (S102).

[0067] Next, the INL evaluation unit 203 detects the INL of the segment-type DAC 202 based on the analog waveform output from the segment-type DAC 202 (S103).

[0068] Next, the INL evaluation unit 203 obtains the maximum absolute value of the INL of the segment-type DAC 202, which was detected based on the analog waveform output from the segment-type DAC 202 (S104).

[0069] Next, the INL evaluation unit 203 determines whether the maximum absolute value of the INL of the segment-type DAC 202 is the minimum (S105). If the maximum absolute value of the INL of the segment-type DAC 202 is the minimum, the INL evaluation unit 203 finishes adjusting the power supply voltage of the thermometer code cell unit of the segment-type DAC 202. On the other hand, if the maximum absolute value of the INL of the segment-type DAC 202 is not the minimum, the INL evaluation unit 203 instructs the power supply voltage supply unit 204 to adjust the power supply voltage of the thermometer code cell unit of the segment-type DAC 202.

[0070] Next, the power supply voltage supply unit 204 adjusts the power supply voltage of the thermometer code cell units of the segment type DAC 202 for each group based on the INL evaluation result by the INL evaluation unit 203, and supplies it to the thermometer code cell units of the segment type DAC 202 (S106). After adjusting the power supply voltage of the thermometer code cell units of the segment type DAC 202, the power supply voltage supply unit 204 returns to process S101.

[0071] Thus, in the fourth embodiment described above, the power supply voltage of the thermometer code cell unit of the segment-type DAC is adjusted based on the INL of the DA conversion output. This allows the power supply voltage of the thermometer code cell to be adjusted so as to compensate for the nonlinearity of the DA conversion output based on the detection result of the INL of the DA conversion output.

[0072] <5. Fifth Embodiment> In the fourth embodiment described above, the power supply voltage of the segment-type DAC thermometer code cell unit was adjusted based on the INL of the DA conversion output. In this fifth embodiment, the power supply voltage of the segment-type DAC thermometer code cell unit is adjusted based on the amplitude of the third harmonic of the DA conversion output.

[0073] Figure 12 is a block diagram showing an example configuration of the power supply voltage evaluation system of a DA conversion circuit according to the fifth embodiment.

[0074] In the figure, this power supply voltage evaluation system adjusts the power supply voltage of the thermometer code cell unit of the segment-type DAC 202 based on the amplitude of the third harmonic of the DA conversion output. This power supply voltage evaluation system comprises an input unit 301, a segment-type DAC 202, an ADC 301, an FFT (Fast Fourier Transformation) unit 302, a third harmonic evaluation unit 303, a code adjustment unit 304, and a power supply voltage supply unit 305.

[0075] The input unit 301 inputs a sine wave digital signal to the segment type DAC 202. The input unit 301 is connected before the segment type DAC 202. In this case, the input unit 301 can receive a single-frequency sine wave digital signal with a sampling frequency of about 10%.

[0076] The ADC 301 performs A / D conversion on the analog signal output from the segment-type DAC 202 and outputs it to the FFT unit 302. The ADC 301 is connected downstream of the segment-type DAC 202.

[0077] The FFT unit 302 performs a Fourier transform on the digital signal output from the ADC 301 and outputs it to the third harmonic evaluation unit 303. The FFT unit 302 is connected downstream of the ADC 301.

[0078] The third harmonic evaluation unit 303 evaluates the amplitude of the third harmonic of the DA conversion output of the segment type DAC 202 based on the Fourier transform result output from the FFT unit 302.

[0079] The code adjustment unit 304 adjusts the control code of the power supply voltage supply unit 305 based on the INL evaluation result by the INL evaluation unit 203. The control code of the power supply voltage supply unit 305 can specify the power supply voltage supplied from the power supply voltage supply unit 305.

[0080] The power supply voltage supply unit 305 adjusts the power supply voltage of the thermometer code cell units of the segment type DAC 202 for each group based on the control code specified by the code adjustment unit 304, and supplies it to the thermometer code cell units of the segment type DAC 202.

[0081] Figure 13 is a flowchart showing the power supply voltage evaluation process of a DA conversion circuit according to the fifth embodiment.

[0082] In the figure, the input unit 301 inputs a sine wave digital signal to the segment type DAC 202 (S201).

[0083] Next, the segment-type DAC 202 performs a DA conversion on the digital signal input from the input unit 201 and outputs an analog signal (S202).

[0084] Next, the FFT unit 302 performs a Fourier transform on the digital signal obtained by AD conversion from the analog signal output from the segment-type DAC 202 and outputs it to the third-harmonic evaluation unit 303 (S203).

[0085] Next, the third harmonic evaluation unit 303 evaluates the amplitude of the third harmonic of the DA conversion output of the segment type DAC 202 based on the Fourier transform result output from the FFT unit 302. At this time, the third harmonic evaluation unit 303 determines whether the amplitude of the third harmonic of the DA conversion output of the segment type DAC 202 is the minimum (S204). If the amplitude of the third harmonic of the DA conversion output of the segment type DAC 202 is the minimum, the third harmonic evaluation unit 303 finishes adjusting the power supply voltage of the thermometer code cell unit of the segment type DAC 202. On the other hand, if the amplitude of the third harmonic of the DA conversion output of the segment type DAC 202 is not the minimum, the third harmonic evaluation unit 303 instructs the code adjustment unit 304 to adjust the control code of the power supply voltage of the thermometer code cell unit of the segment type DAC 202.

[0086] Next, the code adjustment unit 304 adjusts the control code of the power supply voltage supply unit 305 based on the evaluation results from the third harmonic evaluation unit 303 (S205).

[0087] Next, the power supply voltage unit 305 adjusts the power supply voltage of the thermometer code cell units of the segment type DAC 202 for each group based on the control code specified by the code adjustment unit 304, and supplies it to the thermometer code cell units of the segment type DAC 202 (S206). After adjusting the power supply voltage of the thermometer code cell units of the segment type DAC 202, the power supply voltage unit 305 returns to processing S201.

[0088] Thus, in the fifth embodiment described above, the power supply voltage of the thermometer code cell unit of the segment-type DAC is adjusted based on the amplitude of the third harmonic of the DA conversion output. This makes it possible to adjust the power supply voltage of the thermometer code cell so as to compensate for the nonlinearity of the DA conversion output based on the detection result of the third harmonic of the DA conversion output.

[0089] <6. Sixth Embodiment> In the first embodiment described above, the thermometer code cell unit of the segment type DAC was divided into multiple groups, and the power supply voltage for each group was set. In this sixth embodiment, a segment type DAC in which the power supply voltage is set for each group of thermometer code cell units is applied to a communication device.

[0090] Figure 14 is a block diagram showing an example configuration of a communication device to which the DA conversion circuit according to the sixth embodiment is applied.

[0091] In the figure, the communication device comprises a transmitter 400 and a receiver 403. Transmission data transmitted from the transmitter 400 is transmitted to the receiver 403 via a transmission line and received by the receiver 403. The transmitter 400 and receiver 403 are capable of wired communication.

[0092] The transmitter 400 includes a digital signal processing unit 401 and a segment type DAC 402. The segment type DAC 402 is connected downstream of the digital signal processing unit 401. The digital signal processing unit 401 processes the digital signal DIN digitally and outputs it to the segment type DAC 402. The segment type DAC 402 performs a DA conversion on the digital signal DIN processed by the digital signal processing unit 401 and transmits it to the receiver 403. The segment type DAC 402 may be any of the segment type DACs described in the first to third embodiments above. By mounting the segment type DAC 402 in the transmitter 400, long-distance, high-data-rate communication becomes possible.

[0093] Thus, in the sixth embodiment described above, a segment-type DAC in which the power supply voltage is set for each group of thermometer code cell units is applied to the communication device. This makes it possible to improve the linearity of AD conversion of communication data while suppressing an increase in the circuit size of the DA conversion circuit.

[0094] <7. Seventh Embodiment> In the sixth embodiment described above, a segment-type DAC in which the power supply voltage is set for each group of thermometer code cell units was applied to the communication device. In this seventh embodiment, a segment-type DAC in which the power supply voltage is set for each group of thermometer code cell units is applied to the imaging device.

[0095] Figure 15 is a block diagram showing an example configuration of an imaging device to which the DA conversion circuit according to the seventh embodiment is applied.

[0096] In the figure, the imaging device comprises a pixel array unit 111, a vertical scanning circuit 112, a column readout circuit 113, a column signal processing unit 114, a horizontal scanning circuit 115, and a control circuit 116.

[0097] The pixel array section 111 comprises a plurality of pixels PX. The pixels PX are arranged in a matrix along the row direction (also called the horizontal direction) and the column direction (also called the vertical direction). Each pixel PX can form a source follower with the column readout circuit 113 when reading a signal. Each pixel PX is connected to a horizontal drive line HSL for each row and to a vertical signal line VSL for each column. The horizontal drive line HSL drives each pixel PX row by row when reading a signal from each pixel PX. The vertical signal line VSL transmits the pixel signals read from the pixel PX to the column signal processing unit 114 column by column.

[0098] Each pixel PX may be a single pixel, a four-pixel shared pixel, or an eight-pixel shared pixel. Furthermore, the pixel PX may form a Bayer array or a quad-Bayer array. The light received by each pixel PX may be visible light, near-infrared (NIR), short-wavelength infrared (SWIR), ultraviolet light, or X-rays, etc.

[0099] The vertical scanning circuit 112 scans the pixels PX to be read out in the column direction. The vertical scanning circuit 112 may include a vertical register. Here, the vertical scanning circuit 112 can drive each pixel PX row by row via the horizontal drive line HSL when reading a signal from each pixel PX.

[0100] The column readout circuit 113 can configure a source follower with each pixel PX when reading a signal from each pixel PX. In this case, the column readout circuit 113 can change the potential of the vertical signal line VSL for each column based on the charge held in each pixel PX.

[0101] The column signal processing unit 114 processes the signals transmitted from each pixel PX in the column direction. For example, the column signal processing unit 114 can perform correlated double sampling (CDS) processing based on the signals transmitted from each pixel PX in the column direction. The column signal processing unit 114 can also perform analog-to-digital (AD) conversion processing based on the signals transmitted from each pixel PX in the column direction and output an imaging signal Gout. The column signal processing unit 114 includes a column ADC unit 114A and a segment-type DAC 114B.

[0102] The column ADC unit 114A can perform AD conversion processing in parallel for each column. In this case, the column ADC unit 114A can perform AD conversion for each column based on the comparison result between the pixel signal read from the pixel PX and the reference signal REF.

[0103] The segment-type DAC 114B generates a reference signal REF based on the DA conversion of the digital input and outputs it to the column ADC unit 114A. The segment-type DAC 114B may be any of the segment-type DACs described in the first to third embodiments above.

[0104] The horizontal scanning circuit 115 scans the pixels PX to be read out in the row direction. The horizontal scanning circuit 115 may also include a horizontal register.

[0105] The control circuit 116 controls the vertical scanning circuit 112, the column reading circuit 113, the column signal processing unit 114, and the horizontal scanning circuit 115. For example, the control circuit 116 can control the scanning timing in the column direction, the scanning timing in the row direction, the operation timing of the column reading circuit 113, and the processing timing of the column signal processing unit 114. In this case, the control circuit 116 can coordinate the vertical scanning circuit 112, the column reading circuit 113, the column signal processing unit 114, and the horizontal scanning circuit 115 so that the accumulation operation, shutter operation, and read operation are performed for each row in each frame.

[0106] Thus, in the seventh embodiment described above, a segment-type DAC in which the power supply voltage is set for each group of thermometer code cell units is applied to the imaging device. This makes it possible to improve the linearity of AD conversion of pixel signals while suppressing an increase in the circuit size of the DA conversion circuit.

[0107] Furthermore, any of the DA conversion circuits of the first to third embodiments described above can be applied to communication devices and imaging devices, as well as to electronic circuits used in display devices, data processing devices, control devices, measuring devices, or printing devices.

[0108] Furthermore, the embodiments described above are merely examples of how to realize the present technology, and there is a corresponding relationship between the matters in the embodiments and the inventive features in the claims. Similarly, there is a corresponding relationship between the inventive features in the claims and the matters in the embodiments of the present technology that bear the same name. However, the present technology is not limited to the embodiments and can be realized by making various modifications to the embodiments without departing from the gist of the present technology. Also, the effects described herein are merely examples and are not limiting, and there may be other effects.

[0109] Furthermore, this technology can also take the following configurations: (1) A DA conversion circuit comprising a binary code cell on the lower bit side and a thermometer code cell on the upper bit side, wherein the thermometer code cell comprises a first thermometer code cell unit, a second thermometer code cell unit, a first power supply that supplies a first power supply voltage to the first thermometer code cell unit, and a second power supply that supplies a second power supply voltage to the second thermometer code cell unit. (2) The DA conversion circuit according to (1), wherein the binary code cell comprises a reference power supply that supplies a reference power supply voltage to the binary code cell unit. (3) The DA conversion circuit according to (2), wherein the first power supply voltage is lower than the reference power supply voltage and the second power supply voltage is higher than the reference power supply voltage. (4) The DA conversion circuit according to any one of (1) to (3), wherein the first power supply and the second power supply are each variable voltage power supplies. (5) The DA conversion circuit according to (4), wherein the first power supply voltage and the second power supply voltage are adjusted with reference to the reference power supply voltage of the binary code cell. (6) The DA conversion circuit according to any one of (1) to (5), wherein when the thermometer code cell units included in the thermometer code cell are divided into a plurality of groups, the difference in the number of thermometer code cell units included in each group is within 1. (7) The DA conversion circuit according to any one of (1) to (6), wherein the first thermometer code cell unit is arranged on the upper and lower sides of the thermometer code cell, and the second thermometer code cell unit is arranged on the middle side of the thermometer code cell. (8) The DA conversion circuit according to (7), wherein the thermometer code cell comprises a third thermometer code cell unit and a third power supply that supplies a third power supply voltage to the third thermometer code cell unit. (9) The DA conversion circuit according to (8), wherein the third thermometer code cell unit is arranged on the upper and lower middle sides of the thermometer code cell. (10) The DA conversion circuit according to any one of (1) to (9) above, wherein the first power supply voltage and the second power supply voltage are set such that the maximum value of the absolute value of the INL (Integral Nonlinearity) of the DA conversion output is minimized.(11) A DA conversion circuit according to any one of (1) to (10) above, wherein the first power supply voltage and the second power supply voltage are set such that the amplitude of the third harmonic of the DA conversion output is minimized. (12) An imaging device comprising: an imaging unit provided with a plurality of pixels; an AD conversion unit that digitizes the pixel signals based on the comparison result of the pixel signals read from the pixels with a reference signal; and a DA conversion circuit that generates the reference signal based on DA conversion, wherein the DA conversion circuit comprises a binary code cell on the lower bit side and a thermometer code cell on the upper bit side, and the thermometer code cell comprises a first thermometer code cell unit, a second thermometer code cell unit, a first power supply that supplies a first power supply voltage to the first thermometer code cell unit, and a second power supply that supplies a second power supply voltage to the second thermometer code cell unit. (13) An electronic circuit comprising an analog circuit and a DA conversion circuit that generates an analog signal supplied to the analog circuit based on DA conversion, wherein the DA conversion circuit comprises a binary code cell on the lower bit side and a thermometer code cell on the upper bit side, and the thermometer code cell comprises a first thermometer code cell unit, a second thermometer code cell unit, a first power supply that supplies a first power supply voltage to the first thermometer code cell unit, and a second power supply that supplies a second power supply voltage to the second thermometer code cell unit.

[0110] BU Binary code cell MU Thermometer code cell B １ From B ｉ Binary code cell unit T １ From T ｋ , T' １ From T' ｊ , T” １ From T" ｍ Thermometer cord cell unit VD, VD1, VD2 power supply

Claims

1. A DA conversion circuit comprising a binary code cell on the lower bit side and a thermometer code cell on the upper bit side, wherein the thermometer code cell comprises a first thermometer code cell unit, a second thermometer code cell unit, a first power supply that supplies a first power supply voltage to the first thermometer code cell unit, and a second power supply that supplies a second power supply voltage to the second thermometer code cell unit.

2. The DA conversion circuit according to claim 1, wherein the binary code cell comprises a reference power supply that supplies a reference power supply voltage to the binary code cell unit.

3. The DA conversion circuit according to claim 2, wherein the first power supply voltage is lower than the reference power supply voltage, and the second power supply voltage is higher than the reference power supply voltage.

4. The DA conversion circuit according to claim 1, wherein the first power supply and the second power supply are each variable voltage power supplies.

5. The DA conversion circuit according to claim 4, wherein the first power supply voltage and the second power supply voltage are adjusted with reference to the reference power supply voltage of the binary code cell.

6. The DA conversion circuit according to claim 1, wherein when the thermometer code cell units included in the thermometer code cell are divided into a plurality of groups, the difference in the number of thermometer code cell units included in each group is within 1.

7. The DA conversion circuit according to claim 1, wherein the first thermometer code cell unit is arranged on the upper and lower sides of the thermometer code cell, and the second thermometer code cell unit is arranged on the middle side of the thermometer code cell.

8. The DA conversion circuit according to claim 7, wherein the thermometer code cell comprises a third thermometer code cell unit and a third power supply that supplies a third power supply voltage to the third thermometer code cell unit.

9. The DA conversion circuit according to claim 8, wherein the third thermometer code cell unit is arranged on the upper and lower mid-positions of the thermometer code cell.

10. The DA conversion circuit according to claim 1, wherein the first power supply voltage and the second power supply voltage are set such that the maximum value of the absolute value of the INL (Integral Nonlinearity) of the DA conversion output is minimized.

11. The DA conversion circuit according to claim 1, wherein the first power supply voltage and the second power supply voltage are set such that the amplitude of the third harmonic of the DA conversion output is minimized.

12. An imaging device comprising: an imaging unit provided with a plurality of pixels; an AD conversion unit that digitizes the pixel signals based on a comparison result between the pixel signals read from the pixels and a reference signal; and a DA conversion circuit that generates the reference signal based on DA conversion, wherein the DA conversion circuit comprises a binary code cell on the lower bit side and a thermometer code cell on the upper bit side, and the thermometer code cell comprises a first thermometer code cell unit, a second thermometer code cell unit, a first power supply that supplies a first power supply voltage to the first thermometer code cell unit, and a second power supply that supplies a second power supply voltage to the second thermometer code cell unit.

13. An electronic circuit comprising an analog circuit and a DA conversion circuit that generates an analog signal supplied to the analog circuit based on DA conversion, wherein the DA conversion circuit comprises a binary code cell on the lower bit side and a thermometer code cell on the upper bit side, and the thermometer code cell comprises a first thermometer code cell unit, a second thermometer code cell unit, a first power supply that supplies a first power supply voltage to the first thermometer code cell unit, and a second power supply that supplies a second power supply voltage to the second thermometer code cell unit.

Images