High-matching R-2R type DAC circuit based on switch on-resistance

Abstract

The invention relates to a high-matching R-2R type DAC circuit based on switch on-resistance. The circuit comprises a DAC core circuit (1) of R-2R trapezoidal network resistance, a rail-to-rail output buffer (2) and 16 CMOS phase inverters (3). Wherein the DAC core circuit of the R-2R trapezoidal network resistor is responsible for receiving a digital code signal, converting the digital code signal into an analog signal, further inputting the analog signal into the track-to-track output buffer circuit, selecting an NMOS (N-channel Metal Oxide Semiconductor) tube as a switch, and connecting a resistor with the resistance value of 0.5 Ron in series beside the resistor with the resistance value of R, so that the size of the switch is consistent and does not need to be multiplied; the VREF is a reference voltage and is provided by other modules; the output buffer is used for improving the driving capability of the converted analog signal.

Description

Technical Field

[0001] The invention belongs to the technical field of analog integrated circuit design, and in particular relates to a high-matching R-2R type DAC circuit based on switch on-resistance. Background Art

[0002] Whether it is modern 5G communications, high-speed radar detection, instrumentation, industrial control and other professional fields, or general fields such as consumer electronics, automotive electronics, and medical devices, DAC plays an indispensable role in them, and its importance is self-evident. In recent years, with the rapid development of integrated circuit technology, some analog ICs (Integrated Circuit, referred to as IC) have been gradually replaced by digital ICs, but most DACs are still implemented using analog design methods. DAC can not only be used as an independent chip in different fields, but also as a sub-module of the chip to receive and restore the output signal of the on-chip ADC, so the research and development of low-power, wide dynamic range, high-resolution and small-area DACs has become the main exploration direction at present.

[0003] R-2R ladder resistor network is a common DAC structure. In this type of conversion network, each bit only needs one R-2R unit, that is, three unit resistors. For the same N-bit DAC, the traditional weighted resistor DAC structure requires a total of 2 N The number of resistors is greatly reduced, but in the R-2R structure, only 3N resistors are needed. However, in order to achieve high precision, the general R-2R structure DAC is mostly implemented in a combined segmented form. For example, the upper 4 bits use thermometer code, and the remaining low bits use R-2R structure. This increases the complexity of the design and also places high requirements on the switching timing of the high-bit thermometer code.

[0004] The R-2R conversion structure is also divided into two forms: voltage and current output. The main difference between the voltage mode and the current mode lies in the different connection methods of the reference voltage and the output terminal. When the voltage is output, the resistor arm switch switches between the reference voltage VREF and the ground signal; when the current is output, the current of the resistor arm either flows into the output terminal IOUT or into the ground terminal. Compared with the current mode, the voltage mode has the advantages of stable output impedance and small switching glitches.

[0005] After searching, in the prior art, application publication number CN117118448A, a small-area voltage-type R-2R structure DAC with adaptive on-resistance. The present invention changes the resistance value of the traditional 2R resistor in the R-2R resistor network to (2R-Ron), so that the size of the MOS switch from low to high is the same without doubling, achieving the purpose of small area, and at the same time greatly reducing the parasitic capacitance of the MOS, and optimizing the chip layout; and through the adaptive on-resistance analog calibration module, the analog calibration function of the NMOS switch tube and the PMOS switch tube of each bit has equal adaptive on-resistance, so that the R-2R resistor network is well matched, so that the on-resistance of the MOS switch tube does not depend on the characteristics of the MOS switch tube, and can have adaptive stability with PVT, while optimizing DAC performance and improving DAC accuracy, while reducing the impact of PVT changes on DAC performance, and reducing the power consumption of the calibration module, while achieving the purpose of improving DAC performance and accuracy without occupying too much area.

[0006] The on-resistance matching module proposed in this patent uses a sampling MOS of the same size as the switch MOS to simulate the actual switch, and obtains the gate voltages VGN and VGP that match the on-resistance of the NMOS with that of the PMOS. The sampling MOS is always in the on-state in the deep linear region, and the source-drain voltage VDS remains constant. However, in the actual switch MOS, the on-resistance of the MOS will change slightly with the change of VDS, resulting in a deviation between the on-resistance of the sampling MOS and the switch MOS, which may cause a deviation in the calibration of the on-resistance of each bit of the switch, thereby affecting the performance of the DAC.

[0007] When selecting the resistor type of the present invention, by checking the process file, the same type of resistor with a low characteristic deviation coefficient under the process is selected, and the resistor size is kept the same, and only the number of series-parallel resistors is different to achieve the change of different resistance values. Under the same process, the deviation degree of the same resistor is basically the same, which can ensure that the resistance at both ends of each node is the same, so as to achieve high matching. At the same time, when selecting the size of the unit resistor, while ensuring the performance, the size of the unit resistor is made as much larger as possible than the on-resistance of the switch MOS tube, so that when the on-resistance changes slightly due to PVT (the matching resistor and the switch on-resistance are almost completely equal at room temperature), because R and 2R and the matching resistor R ON The size and type are the same, only the quantity is different, so their overall fluctuation trend is the same, which can ensure matching, and R is much larger than the matching resistance R ON Therefore, since the change of the on-resistance of the MOS tube has little effect on the matching between the actual R, it has little effect on the performance of the DAC.

[0008] A matching resistor with a resistance of Rg is connected in series next to each resistor with a resistance of R. The switch size of each bit is the same. Assuming that the switch equivalent resistance is Ron, for each node, the resistance looking down is 2R+R on , the resistance looking backward is Rgi(i=0,1,2,…,n-1,n) is equal to Therefore, all switches of the present invention have the same size, which significantly reduces the circuit area and the parasitic capacitance of high-order MOS switches, especially, so that the performance of DAC is better.

[0009] The switch types of the present invention are all NMOS switches, and PMOS switches and complementary CMOS switches are not selected. Since NMOS tubes have certain losses when transmitting high voltages, although the selection range of reference voltages is limited to a certain extent, NMOS switches are fast and can quickly respond to changes in control signals. They also have low power consumption and consume almost no current in the off state, and have low manufacturing costs. Summary of the invention

[0010] The present invention aims to solve the above problems of the prior art. A high-matching R-2R type DAC circuit based on switch on-resistance is proposed. The technical solution of the present invention is as follows:

[0011] A high-matching R-2R type DAC circuit based on switch on-resistance comprises: an R-2R type DAC core circuit (1), a rail-to-rail analog buffer (2) and 16 CMOS inverters (3), wherein the R-2R type DAC core circuit (1) is used to receive a 16-bit digital signal processed by a front-end path and convert it into a corresponding analog signal for output; the rail-to-rail analog buffer (2) is used to receive the analog signal converted by the R-2R type DAC core circuit, the waveform of the analog signal remains unchanged before and after passing through the buffer, mainly increasing the driving capability of the analog signal so that the final output signal has a load carrying capacity; the inverter (3) is used to generate a signal for controlling the closing and closing of different branches; the input signals are respectively a reference low potential GND, a power supply VDD, a reference voltage VREF, and a 16-bit digital code value for controlling the opening and closing of each switch, and the final output is the output VOUT of the buffer.

[0012] Furthermore, the R-2R type DAC core circuit (1) comprises: the R-2R resistor network is a ladder-shaped mesh resistor network, wherein there are 15 resistors each having a resistance value of R, 17 resistors each having a resistance value of 2R, 15 matching resistors each having a resistance value of Rg, and 17 switches, each of which is composed of two NMOS switches of the same size.

[0013] Furthermore, in the switch equivalent circuit of the R-2R type DAC core circuit (1), the input end of the inverter A is respectively connected to the 16-bit digital signal Si and is connected to the gate of the switch pair NMOS tube M1, i=0, 1, 2..., 14, 15, the output end is respectively connected to the gate of the NMOS tube M2 of 15 switches, the source of the NMOS tube M1 is connected to the reference low potential GND, the source of the NMOS tube M2 is connected to the reference voltage VREF, the drain of the NMOS tube M1 is connected to the switch equivalent on-resistance R ON i is connected to the drain end of M2.

[0014] Furthermore, in the switch equivalent circuit of the R-2R type DAC core circuit (1), if the digital code value of any bit input is high, the NMOS tube M1 is turned on, that is, it is in the linear region, and the reference potential VREF is transmitted at this time. On the contrary, if the digital code input is low, the NMOS tube M2 is turned on, and the reference low potential GND is transmitted at this time. The R-2R type DAC circuit generates an output voltage corresponding to the input code value. Only one of the NMOS tubes M1 and M2 is always in the on state, and the other is off;

[0015] In the R-2R type DAC core circuit (1), 15 resistors with a resistance value of R and 15 resistors with a resistance value of Rgi are connected in series; one end of the resistor with a resistance value of 2R is sequentially connected to the node between the resistors with a resistance value of R and the resistor with a resistance value of Rgi, and the other end is respectively connected to the drain end of each NMOS switch.

[0016] Furthermore, in the switch equivalent circuit of the R-2R type DAC core circuit, the sizes of the NMOS tubes M1 and M2 in the 17 independent switch combinations are the same, and both switch types are NMOS tubes.

[0017] Furthermore, assuming that the switch equivalent resistance is Ron, for node a, the resistance looking backward and downward is 2R+R on ; For node b, the resistance looking downward is 2R+R on , the resistance looking backward is so For node c, the resistance looking downward is also 2R+Ron, and the resistance looking backward is So here Similarly, for each node, the resistance looking down is 2R+R on , the resistance looking backward is Rgi is equal to

[0018]

[0019] Furthermore, the R-2R type DAC core circuit is also connected to an input stage that adopts a constant rail-to-rail input, that is, a complementary differential input pair of PMOS and NMOS in parallel, and the output stage adopts an analog buffer in the form of class AB output, so that the final output VOUT has a certain load capacity.

[0020] Furthermore, in the rail-to-rail analog buffer (2), the in-phase input terminal of the rail-to-rail analog buffer (2) is connected to the output terminal of the R-2R type DAC core, and the inverting input terminal is connected to its own output terminal, so as to form a gain negative feedback; the output terminal V OUT With load resistance R CLOD One end is connected to R CLOD The other end is connected to the reference low potential ground and the load capacitor C CLOD One end is connected to the load capacitor C CLOD The other end and the output terminal of the buffer V OUT connected.

[0021] The advantages and beneficial effects of the present invention are as follows:

[0022] 1. In order to obtain an R-2R type DAC circuit with high matching based on the switch on-resistance, the width-to-length ratio W / L of the resistor (the width-to-length ratio of the resistor of the present invention) is The width-to-length ratio of a resistor is W / L. For resistors with the same resistance value, the width-to-length ratio can be different. The area of ​​resistors with different widths and lengths is also different. For matching and layout purposes, the smallest W is generally not selected) to ensure that the W / L of each resistor is the same, which increases the matching of resistors; the size of each bit switch is the same, which reduces the difficulty of matching and greatly reduces the area; and the resistance value of the unit resistor is reasonably selected (the resistance value is the size of the resistor. In the process library, ( The block resistance of the selected resistor) By controlling the size of the unit resistor, the size of each resistor in the circuit is made the same as much as possible, and the specific resistance value is changed only by changing the number of series and parallel resistors to increase matching), the specific resistance value is changed only by changing the number of series and parallel resistors to make the matching resistor and the switch on-resistance match better, while reducing the area without significantly affecting the overall performance of the DAC.

[0023] 2. The proposed R-2R DAC circuit with high matching based on switch on-resistance has the advantages of low cost, small area, high precision and conducive to integration. The proposed R-2R DAC circuit with high matching based on switch on-resistance can be realized only by MOS tube switch and resistor, avoiding the use of capacitor to increase the chip area, and has the advantages of cost saving, low power consumption and high integration.

[0024] 3. The proposed R-2R DAC circuit with high matching based on switch on-resistance is subsequently processed by a rail-to-rail analog buffer, which increases the stability and driving capability of the conversion signal and has high reliability. In the entire buffer circuit, the circuit achieves a wide swing output range through a rail-to-rail structure and a class AB structure, and the settling time is sufficient.

[0025] The circuit proposed by the present invention uses matching resistors to improve the problem that the traditional circuit switch size is too large and thus leads to a large area. For the traditional 16-bit voltage-type R-2R structure, if the aspect ratio of the lowest-bit MOS switch is Due to the matching relationship, the width-to-length ratio of each higher bit needs to be doubled, so the width-to-length ratio of the highest bit switch is The circuit requires a large MOS tube size and area. In the present invention, a matching resistor with a resistance value of Rg is connected in series next to each resistor with a resistance value of R. The switch size of each bit is the same. Assuming that the switch equivalent resistance is Ron, for the first node, the resistance looking backward and downward is 2R+R on ; For the second node, the resistance looking down is 2R+R on , the resistance looking backward is so Similarly, for each node, the resistance looking down is 2R+R on , the resistance looking backward is Equal to Therefore, all the switch sizes of the present invention are the same, which significantly reduces the circuit area and the parasitic capacitance of the high-bit MOS switch, especially, so that the performance of the DAC is better. In addition, when selecting the resistor type of the present invention, by checking the process file, the same type of resistor with a lower characteristic deviation coefficient under the process is selected, and the resistor size remains the same, and only the number of series-parallel resistors is different to achieve different resistance values. Under the same process, the deviation degree of the same resistor is basically the same, which can ensure that the resistors at both ends of each node are the same, so as to achieve high matching. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The preferred embodiment provided by the present invention is a schematic diagram of the structure of a traditional 16-bit R-2R voltage-type DAC circuit.

[0027] Figure 2 The present invention provides a 16-bit R-2R DAC circuit structure diagram based on switch on-resistance and high matching.

[0028] Figure 3 It is a schematic diagram of the bias circuit structure of a rail-to-rail output analog buffer.

[0029] Figure 4It is a schematic diagram of the main circuit structure of the rail-to-rail output analog buffer.

[0030] Figure 5 is the transient simulation result of the proposed circuit.

[0031] Figure 6 It is an equivalent structure diagram of the switch of the preferred embodiment of the present invention. DETAILED DESCRIPTION

[0032] The following will describe the technical solutions in the embodiments of the present invention in detail in conjunction with the accompanying drawings in the embodiments of the present invention. The described embodiments are only part of the embodiments of the present invention.

[0033] The technical solution of the present invention to solve the above technical problems is:

[0034] The traditional 16-bit R-2R DAC structure is as follows Figure 1 As shown, to ensure the matching of resistance, the on-resistance of the switch at the higher position should be smaller than that at the lower position, and twice smaller than that at the previous position. According to the on-resistance formula When V GS -V TH When the on-resistance is consistent, it is related to the width-to-length ratio. That is, for a 16-bit R-2R DAC, the width-to-length ratio of the highest-bit switch is twice that of the lowest-bit switch. 16 times, the area will be quite large.

[0035] like Figure 2 As shown, a high-matching R-2R type DAC circuit based on switch on-resistance is characterized in that it includes: an R-2R DAC core resistor ladder circuit and a rail-to-rail analog buffer, wherein the R-2R DAC core circuit is used to receive a 16-bit digital code signal processed by a front-end path and convert it into a corresponding analog signal output, and the rail-to-rail analog buffer is used to receive the analog signal converted by the R-2R type DAC core circuit to increase its driving capability; the inverter is used to generate a signal to control the closing and closing of different branches; the input signals are respectively a reference low potential GND, a power supply VDD, a reference voltage VREF, and a 16-bit digital code value for controlling the on and off of each switch, and the final output is the output VOUT of the buffer.

[0036] The R-2R DAC resistor ladder network circuit includes: 15 resistors with a resistance value of R, 17 resistors with a resistance value of 2R, and 15 resistors with a resistance value of Rg (i.e., 0.5R ON) matching resistors, 17 switches, each switch is composed of two NMOS switches of the same size, and 16 CMOS inverters. Further, in the rail-to-rail analog buffer, the buffer processes the output signal of the R-2R DAC resistor ladder network circuit to give it a certain driving capability, and then outputs it. The non-inverting input terminal of the buffer is connected to the output terminal of the R-2R DAC resistor ladder network circuit, and the inverting input terminal is connected to its own output terminal to form a gain negative feedback. The output terminal V OUT With load resistance R CLOD One end is connected to R CLOD The other end is connected to the reference low potential ground and the load capacitor C CLOD One end is connected to the load capacitor C CLOD The other end and the output terminal of the buffer V OUT connected.

[0037] The input end of the inverter Ai (i = 0, 1, 2 ..., 14, 15) is respectively connected to the 16-bit digital code signal Si (i = 0, 1, 2 ..., 14, 15) and is connected to the gate of the switch pair NMOS tube M2 (taking the switch corresponding to the 16th digital code as an example), and the output end is respectively connected to the gate of the NMOS tube M3 of the 16 switches. The source of the NMOS tube M2 is connected to the reference low potential GND, the source of the NMOS tube M3 is connected to the reference voltage VREF, the drain of the NMOS tube M2 is connected to the switch equivalent on-resistance R ON And the drain end of M3 is connected.

[0038] In the switch of the R-2R DAC resistor ladder network circuit, if any bit of the input digital code is high, the NMOS tube M2 is turned on, that is, it is in the linear region, and the reference potential VREF is transmitted at this time. On the contrary, if the input digital code is low, the NMOS tube M3 is turned on, and the reference low potential is transmitted at this time. The R-2R DAC circuit generates an output voltage corresponding to the input digital code value. Only one of the NMOS tubes M2 and M3 is always in the on state, and the other is off.

[0039] In the ladder resistor network, 15 resistors with a resistance value of R and 15 resistors with a resistance value of Rg are connected in series with each other; one end of the resistor with a resistance value of 2R is connected to the nodes between the resistors with a resistance value of R and a resistance value of Rg in sequence, and the other end is connected to the drain end of each NMOS switch respectively.

[0040] In the switches of the R-2R DAC resistor ladder network circuit, the sizes of NMOS tubes M2 and M3 in each individual switch combination are the same, and both switches are NMOS tubes. The closing or opening of each branch is controlled by 17 switch combinations, wherein the branch controlled by the SW switch is always in the on state when the circuit is working. In addition, the 16-bit R-2R DAC circuit is also connected to an analog buffer with both input and output rail-to-rail, so that the final output VOUT has a certain load capacity and realizes a wide swing output.

[0041] Figure 3 The bias circuit of the rail-to-rail buffer provides the required bias voltage for the buffer, and the initial bias current is provided by other modules. Figure 4 The rail-to-rail buffer structure adopted has a constant rail-to-rail input at the input stage, namely, a complementary differential input pair of POMs and NMOSs in parallel, and a class AB output at the output stage, which can increase the output swing.

[0042] According to the Thevenin equivalent theorem, the Thevenin equivalent is applied to each node in turn to obtain the contribution voltage of each node. Then, according to the superposition principle, the final output VOUT of the circuit can be obtained as (b 15 b 14 …b 1 b 0 is a 16-digit code).

[0043] When selecting the resistor type for the circuit, resistors of the same type with a lower characteristic deviation coefficient under the process are selected, and the size of the resistors remains constant. The changes in different resistance values ​​are achieved by different numbers of series and parallel connections. The 2R resistor is obtained by connecting two identical Rs in series, and the matching resistor Rg is obtained by connecting a certain number of Rs in parallel to achieve high matching.

[0044] Figure 5 The 16-bit ideal ADC is used as the 16-bit digital code value provided by the DAC. The transient simulation results obtained under the pre-simulation, without calibration, can achieve an effective accuracy of 12.2bit and a SFDR of 79.6dB. When 011...111 switches to 100...00, a larger burr than at other times will be generated, which is a normal phenomenon and can be improved through thermometer code or other methods in the future.

[0045] The R-2R type DAC core circuit is also connected to an input stage that uses a constant rail-to-rail input, that is, a complementary differential input pair of PMOS and NMOS in parallel, and the output stage uses an analog buffer in the form of a class AB output, so that the final output VOUT has a certain load capacity.

[0046] The present invention selects two NMOS switch tubes as switches for a certain position, instead of selecting a switch tube composed of two PMOS switch tubes, one NMOS switch tube and a PMOS switch tube as a switch. The two NMOS switches for each position have the same size, which is more convenient for matching resistors. As long as the reference voltage value is reasonably selected, the NMOS switch can be used as a switch tube, and when the NMOS switch is connected to the ground relative to the PMOS switch, the MOS tube working state will not be abnormal.

[0047] In the present invention, a matching resistor with a resistance value of Rg is connected in series next to each resistor with a resistance value of R. The switch size of each bit is the same. Assuming that the switch equivalent resistance is Ron, for node a, the resistance looking backward and downward is 2R+R on ; For node b, the resistance looking downward is 2R+R on , the resistance looking backward is so For node c, the resistance looking downward is also 2R+Ron, and the resistance looking backward is So here Similarly, for each node, the resistance looking down is 2R+R on , the resistance looking backward is Rgi(i=0,1,2,…,14,15) is equal to

[0048] When selecting the resistor type of the present invention, the same type of resistor with a lower characteristic deviation coefficient under the process can be selected, and the resistor size remains the same. The change of different resistance values ​​is achieved by different numbers of series and parallel connections. Under the same process, the deviation degree of the same resistor is basically the same, which can ensure that the resistance at both ends of each node is the same, so as to achieve high matching.

[0049] For the traditional 16-bit voltage-type R-2R structure, if the aspect ratio of the lowest-bit MOS switch is Due to the matching relationship, the width-to-length ratio of each higher bit needs to be doubled, so the width-to-length ratio of the highest bit switch is The circuit requires a large MOS tube size and area, but all switches of the present invention have the same size, which significantly reduces the circuit area and the parasitic capacitance of the high-order MOS switch, especially, so that the performance of the DAC is better.

[0050] The systems, devices, modules or units described in the above embodiments may be implemented by computer chips or entities, or by products with certain functions.

[0051] It should also be noted that the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, commodity or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, commodity or device. In the absence of more restrictions, the elements defined by the sentence "comprises a ..." do not exclude the existence of other identical elements in the process, method, commodity or device including the elements.

[0052] The above embodiments should be understood to be only used to illustrate the present invention and not to limit the protection scope of the present invention. After reading the contents of the present invention, technicians can make various changes or modifications to the present invention, and these equivalent changes and modifications also fall within the scope defined by the claims of the present invention.

Claims

1. A high-matching R-2R type DAC circuit based on switch on-resistance, characterized in that: include: An R-2R type DAC core circuit (1), a rail-to-rail analog buffer (2) and 16 CMOS inverters (3), wherein the R-2R type DAC core circuit (1) is used to receive a 16-bit digital signal processed by a front-end path and convert it into a corresponding analog signal for output; the rail-to-rail analog buffer (2) is used to receive the analog signal converted by the R-2R type DAC core circuit, the waveform of the analog signal remains unchanged before and after passing through the buffer, mainly increasing the analog signal driving capability, so that the final output signal has a load carrying capacity; the inverter (3) is used to generate a signal for controlling the closing and closing of different branches; the input signals are respectively a reference low potential GND, a power supply VDD, a reference voltage VREF, and a 16-bit digital code value for controlling the on and off of each switch, and the final output is the output VOUT of the buffer.

2. The high-matching R-2R type DAC circuit based on switch on-resistance according to claim 1, characterized in that: The R-2R type DAC core circuit (1) comprises: an R-2R resistor network which is a ladder-shaped mesh resistor network, wherein there are 15 resistors each having a resistance value of R, 17 resistors each having a resistance value of 2R, 15 matching resistors each having a resistance value of Rg, and 17 switches, each of which is composed of two NMOS switches of the same size.

3. The high-matching R-2R type DAC circuit based on switch on-resistance according to claim 2, characterized in that: In the switch equivalent circuit of the R-2R type DAC core circuit (1), the input end of the inverter A is respectively connected to the 16-bit digital signal Si and is connected to the gate of the switch pair NMOS tube M1, i=0, 1, 2..., 14, 15, the output end is respectively connected to the gate of the NMOS tube M2 of 15 switches, the source of the NMOS tube M1 is connected to the reference low potential GND, the source of the NMOS tube M2 is connected to the reference voltage VREF, the drain of the NMOS tube M1 is connected to the switch equivalent on-resistance R ON i is connected to the drain end of M2.

4. The high-matching R-2R type DAC circuit based on switch on-resistance according to claim 2 or 3, characterized in that: In the switch equivalent circuit of the R-2R type DAC core circuit (1), if the digital code value of any bit input is high, the NMOS tube M1 is turned on, that is, it is in the linear region, and the reference potential VREF is transmitted at this time. On the contrary, if the digital code input is low, the NMOS tube M2 is turned on, and the reference low potential GND is transmitted at this time. The R-2R type DAC circuit generates an output voltage corresponding to the input code value. Only one of the NMOS tubes M1 and M2 is always in the on state, and the other is off; In the R-2R type DAC core circuit (1), 15 resistors with a resistance value of R and 15 resistors with a resistance value of Rgi are connected in series; one end of the resistor with a resistance value of 2R is sequentially connected to the node between the resistors with a resistance value of R and the resistor with a resistance value of Rgi, and the other end is respectively connected to the drain end of each NMOS switch.

5. The high-matching R-2R type DAC circuit based on switch on-resistance according to claim 2 or 3, characterized in that: In the switch equivalent circuit of the R-2R type DAC core circuit, the sizes of the NMOS tubes M1 and M2 in the 17 independent switch combinations are the same, and both switch types are NMOS tubes.

6. The high-matching R-2R type DAC circuit based on switch on-resistance according to claim 2, characterized in that: Assuming the switch equivalent resistance is Ron, for node a, the resistance looking backward and downward is 2R+R on ; For node b, the resistance looking downward is 2R+R on , the resistance looking backward is so For node c, the resistance looking downward is also 2R+Ron, and the resistance looking backward is So here Similarly, for each node, the resistance looking down is 2R+R on , the resistance looking backward is Rgi is equal to 7. The high-matching R-2R type DAC circuit based on switch on-resistance according to claim 1, characterized in that: The R-2R type DAC core circuit is also connected to an input stage that uses a constant rail-to-rail input, that is, a complementary differential input pair of PMOS and NMOS in parallel, and the output stage uses an analog buffer in the form of a class AB output, so that the final output VOUT has a certain load capacity.

8. The high-matching R-2R type DAC circuit based on switch on-resistance according to claim 7, characterized in that: In the rail-to-rail analog buffer (2), the in-phase input terminal of the rail-to-rail analog buffer (2) is connected to the output terminal of the R-2R type DAC core, and the inverting input terminal is connected to its own output terminal, so as to form a gain negative feedback; the output terminal V OUT With load resistance R CLOD One end is connected to R CLOD The other end is connected to the reference low potential ground and the load capacitor C CLOD One end is connected to the load capacitor C CLOD The other end and the output terminal of the buffer V OUT connected.

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