Improved high-precision R-2R type DAC structure

Abstract

The application discloses an improved high-precision R-2R type DAC structure and belongs to the field of electronic circuits, comprising DAC high-bit encoding, DAC low-bit encoding, current trimming encoding and an amplification output stage with adaptable input range; the DAC high-bit encoding adopts m-bit thermometer code, the DAC low-bit encoding adopts n-bit binary code, and the current trimming encoding adopts t-bit binary code to trim the error of the lowest bit R value part in the binary code. The application not only solves the problem of large error caused by too many bits and realizes the super-high-precision R-2R type DAC output, but also adds current calibration, can independently control the improvement of precision, and theoretically, the precision can be infinite. The rear stage is connected with an adjustable input range operational amplifier, which can flexibly adapt to various application scenarios and improve the precision and reliability of related application products.

Description

Technical Field

[0001] This invention relates to the field of electronic circuit technology, and in particular to an improved high-precision R-2R type DAC structure. Background Technology

[0002] R-2R resistor-type DACs have a simple structure and clear control logic, making them relatively easy to implement. However, as the number of bits increases, the resistor area on the chip layout becomes excessively large, making it difficult to control process errors and leading to larger output errors and decreased accuracy. Therefore, many high-precision DACs do not choose the R-2R structure as their main structure. To address this issue, there is an urgent need to propose an improved high-precision R-2R structure. Summary of the Invention

[0003] The purpose of this invention is to provide an improved high-precision R-2R DAC structure to achieve ultra-high precision R-2R DAC output and improve the accuracy and reliability of related application products.

[0004] To solve the above technical problems, the present invention provides an improved high-precision R-2R type DAC structure, including DAC high-bit encoding, DAC low-bit encoding, current trimming encoding, and an amplification output stage with an adaptable input range;

[0005] The DAC high-order encoding uses an m-bit thermometer code, the DAC low-order encoding uses an n-bit binary code, and the current adjustment encoding uses a t-bit binary code to adjust the error of the least significant bit R value in the binary code.

[0006] Optionally, the DAC low-order encoding includes n resistors 2R and n resistors R. The n resistors R are connected in series to form a resistor chain. The first end of each resistor 2R is grounded or connected to a reference voltage Vref through a single-pole double-throw switch. The second end of each resistor 2R is connected between every two resistors R.

[0007] Optionally, the first end of the resistor chain is connected to the amplification output stage, and the second end is grounded through a resistor R.

[0008] Optionally, the DAC high-order encoding includes m resistors R, with the first end of each resistor R connected to ground or reference voltage Vref via a single-pole double-throw switch, and the second end of each resistor R connected to the amplification output stage.

[0009] Optionally, the current adjustment code includes t+1 MOSFETs M0, M1, ..., M t and t switches K1~K t ; MOSFETs M0, M1, ..., M t The drain terminal is connected to VDD, and t MOSFETs M1, ..., Mt The source terminals are respectively connected to switches K1 to K t Connected to the second end of the resistor chain, MOSFETs M1, ..., M t The gate terminals of MOSFETs M1 and M2 are interconnected and connected to the gate terminals of MOSFET M0; the current received by MOSFET M1 is 1 / 2 of the current to be replicated; the current received by MOSFET M2 is 1 / 4 of the current to be replicated; and so on, the current received by MOSFET M... t The current obtained is 1 / t of the current to be replicated.

[0010] Optionally, the amplification output stage includes switch K0, switch K1, resistor R0, variable resistor θR, amplifier AMP2, resistor αR, and resistor βR; the positive input terminal of amplifier AMP2 is connected to both switch K0 and switch K1 through resistor R0, and switch K1 is grounded through variable resistor θR; the negative input terminal of amplifier AMP2 is grounded through resistor αR, and the output terminal is connected to its own negative input terminal through resistor βR.

[0011] Optionally, the source terminal of MOSFET M0 is connected to the drain terminal of MOSFET N, the source terminal of MOSFET N is grounded through a resistor R, the gate terminal of MOSFET N is connected to the output terminal of amplifier AMP1, the positive input terminal of amplifier AMP1 is connected to the reference voltage Vref, and the negative input terminal is connected to the source terminal of MOSFET N.

[0012] The improved high-precision R-2R DAC structure provided by this invention includes a DAC high-bit encoding, a DAC low-bit encoding, a current-adjusting encoding, and an amplification output stage with an adaptable input range. The DAC high-bit encoding uses m-bit thermometer code, the DAC low-bit encoding uses n-bit binary code, and the current-adjusting encoding uses t-bit binary code to adjust the error of the least significant R-value portion of the binary code. This invention not only solves the problem of large errors due to a large number of bits, but also incorporates current calibration, which can be autonomously controlled to improve accuracy; theoretically, the accuracy can be infinite. The subsequent stage connects to an operational amplifier with an adjustable input range, allowing for flexible adaptation to various application scenarios. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of an improved high-precision R-2R type DAC structure provided by the present invention;

[0014] Figure 2 This is a schematic diagram of a DAC structure considering the influence of the calibration current I independently;

[0015] Figure 3 This is a schematic diagram of a DAC structure considering the influence of digital codes independently. Detailed Implementation

[0016] The improved high-precision R-2R DAC structure proposed in this invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of this invention will become clearer from the following description and claims. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of this invention.

[0017] This invention provides an improved high-precision R-2R type DAC structure, the structure of which is as follows: Figure 1 As shown, it includes DAC high-bit encoding, DAC low-bit encoding, current adjustment encoding, and an amplification output stage with an adaptable input range; the DAC high-bit encoding uses m-bit thermometer code, the DAC low-bit encoding uses n-bit binary code, and the current adjustment encoding uses t-bit binary code to adjust the error of the least significant bit R value in the binary code.

[0018] The DAC low-order encoding includes n-1 resistors 2R and n resistors R. The n resistors R are connected in series to form a resistor chain. The first end of each resistor 2R is grounded through a single-pole double-throw switch or connected to a reference voltage Vref. The second end of each resistor 2R is connected between every two resistors R. The first end of the resistor chain is connected to the amplification output stage, and the second end is grounded through a resistor R.

[0019] The DAC high-order encoding includes m resistors R. The first end of each resistor R is grounded or connected to a reference voltage Vref through a single-pole double-throw switch. The second end of each resistor R is connected to the amplification output stage.

[0020] The amplification output stage includes switch K0, switch K1, resistor R0, variable resistor θR, amplifier AMP2, resistor αR, and resistor βR. The positive input terminal of amplifier AMP2 is connected to both switch K0 and switch K1 through resistor R0, and switch K1 is grounded through variable resistor θR. The negative input terminal of amplifier AMP2 is grounded through resistor αR, and the output terminal is connected to its own negative input terminal through resistor βR.

[0021] The current adjustment code includes t+1 MOSFETs M0, M1, ..., M t and t switches K1~K t ; MOSFETs M0, M1, ..., M t The drain terminal is connected to VDD, and t MOSFETs M1, ..., M t The source terminals are respectively connected to switches K1 to K t Connected to the second end of the resistor chain, MOSFETs M1, ..., M tThe gate terminals of MOSFETs M1 and M2 are interconnected and connected to the gate terminals of MOSFET M0; the current received by MOSFET M1 is 1 / 2 of the current to be replicated; the current received by MOSFET M2 is 1 / 4 of the current to be replicated; and so on, the current received by MOSFET M... t The current obtained is 1 / t of the current to be replicated. Because the resistance deviation is fixed, after the wafer fabrication is completed, the switching of the MOSFETs in the calibration structure is controlled according to the deviation measured in the first measurement. Different proportions of current can be injected into the DAC to modify the output voltage under different offset conditions. It should be noted that the MOSFET ratio in the two-level code is not unique, and the total value can also exceed the value of Vref. The input range of the op-amp AMP2 in the amplification output stage may not reach the wide input range of 0-Vref. It is necessary to first reduce the voltage output of the DAC to the operating range of the op-amp, and then amplify it by the same factor. The source terminal of the MOSFET M0 is connected to the drain terminal of the MOSFET N. The source terminal of the MOSFET N is grounded through a resistor R. The gate terminal of the MOSFET N is connected to the output terminal of the amplifier AMP1. The positive input terminal of the amplifier AMP1 is connected to the reference voltage Vref, and the negative input terminal is connected to the source terminal of the MOSFET N.

[0022] The relationship between the DAC output and input can be analyzed using Thevenin's law, etc.

[0023] The circuit is divided into two parts:

[0024] 1) Independently consider the influence of the calibration current I, and abstract the digital code value as a voltage source. In this case, all values ​​should be grounded, such as... Figure 2 As shown,

[0025] According to mathematical induction:

[0026] The following relationship can be derived: Where τ is the calibration current replication coefficient and ξ is the voltage division coefficient of the resistor network.

[0027] Finally, it was deduced that

[0028] The calculation process for the voltage division coefficient ξ of the resistor network is as follows:

[0029] Looking in from the current injection point, the current passes through two resistor network branches. One branch consists of a resistor R connected to ground, and the other branch comprises the binary code resistor network and the thermometer resistor network. Treating the thermometer code resistor network as an equivalent circuit, the equivalent resistance is... The equivalent resistance of the two-level coding resistor network is obtained by treating it as an equivalent circuit. in X0 = 2, Y0 = 3, z is an ordinal variable; the total equivalent resistance is As the iteration order increases, The range of equivalent resistance is Therefore, the current flowing to V0 is The current flowing through resistor 2R will also be shunted by a similar principle. Similarly, it can be deduced that...

[0030] 2) Considering the influence of the digital code independently, the calibration current branch is treated as an open circuit, such as... Figure 3 As shown, based on the characteristics of the basic R-2R circuit structure, the output voltage is: Equivalent resistance is

[0031] The final V out =V out1 +V out2 calibration factor The value of this parameter is determined by the number of switching transistors that are turned on. It is not limited to the form of a two-level code, and the ratio of transistors can also be increased according to the adjustment requirements.

[0032] in Figure 1 Equivalent resistance factor in Where the equivalent voltage factor is The input of op-amp AMP2 depends on Where θ is the proportional coefficient of the adjustable grounding resistor, and the following relationship must be strictly guaranteed:

[0033] The thermometer code and binary code are selected based on project design experience and accuracy. Consider the case of a 16-bit DAC with accuracy controlled within ±0.5LSB. In this case, according to project design experience, m=15, n=12, t=16, and the input range of op-amp AMP2 is 0-0.4Vref.

[0034] Based on the above formula derivation, the parameters are:

[0035] The equivalent resistance factor is op-amp input factor is The variable resistance adjustment factor is The gain factor of the proportional amplifier is The voltage divider coefficient of the resistor network is ξ≈9, and the equivalent voltage factor is

[0036] If the output voltage deviates by Δ, the calibration factor is used to achieve the required accuracy.

[0037] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A modified high-precision R-2R type DAC structure, characterized in that, The DAC high-bit encoding, the DAC low-bit encoding, the current trimming encoding and the amplification output stage with adaptable input range are included. The DAC high-bit encoding adopts m-bit thermometer code, the DAC low-bit encoding adopts n-bit binary code, and the current trimming encoding adopts t-bit binary code to trim the error of the lowest bit R value part in the binary code. The current adjustment code includes t+1 MOSFETs M0, M1, ..., M t and t switches K1~K t ; MOSFETs M0, M1, ..., M t The drain terminal is connected to VDD, and t MOSFETs M1, ..., M t The source terminals are respectively connected to switches K1~K t Connected to the second end of the resistor chain, MOSFETs M1, ..., M t The gate terminals are interconnected and connected to the gate terminals of MOSFET M0; MOSFET The current received is half of the current to be replicated; MOSFET The current received is 1 / 4 of the current to be replicated; and so on, for the MOSFET... The current obtained is 1 / t of the current to be replicated; The source end of the mos transistor M0 is connected to the drain end of the mos transistor N, the source end of the mos transistor N is connected to the ground through a resistor R, the gate end of the mos transistor N is connected to the output end of the amplifier AMP1, the positive input end of the amplifier AMP1 is connected to the reference voltage Vref, and the negative input end is connected to the source end of the mos transistor N.

2. The modified high-precision R-2R type DAC structure according to claim 1, wherein, The DAC low-bit encoding includes n-1 resistors 2R and n resistors R, the n resistors R are connected in series to form a resistor chain, the first end of each resistor 2R is connected to the ground or the reference voltage Vref through a single-pole double-throw switch, and the second end of each resistor 2R is connected between each two resistors R.

3. The modified high-precision R-2R type DAC structure according to claim 2, characterized in that, The first end of the resistor chain is connected to the amplification output stage, and the second end is connected to the ground through a resistor R.

4. The modified high-precision R-2R type DAC structure according to claim 1, wherein, The DAC high-bit encoding includes m resistors R, the first end of each resistor R is connected to the ground or the reference voltage Vref through a single-pole double-throw switch, and the second end of each resistor R is connected to the amplification output stage.

5. The modified high-precision R-2R type DAC structure according to claim 1, wherein, The amplification output stage includes switches K0 and K1, a resistor R0, a variable resistor θR, an amplifier AMP2, a resistor αR and a resistor βR; the positive input end of the amplifier AMP2 is connected to the switches K0 and K1 through the resistor R0, the switch K1 is connected to the ground through the variable resistor θR; the negative input end of the amplifier AMP2 is connected to the ground through the resistor αR, and the output end is connected to the negative input end through the resistor βR.

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