DA conversion circuit with high-precision reference voltage

Abstract

According to the technical scheme, the DA conversion circuit with the high-precision reference voltage comprises a high-precision reference voltage chip with the model number of SW688 and a digital-to-analog conversion chip with the model number of SDA8412, and a first pin of the high-precision reference voltage chip is directly connected with the VREFH end of the digital-to-analog conversion chip without passing through any series resistor; the fifteenth pin of the high-precision reference voltage chip is directly connected with the VREFL end of the digital-to-analog conversion chip without passing through any series resistor. For a module which has completed design and production, the reference voltage precision can be adjusted by modifying a series resistor, so that ineffective re-design change is avoided, or instability caused by environmental factor change of reference voltage output correction by using external resistor adjustment is avoided.

Description

Technical Field

[0001] The utility model relates to the influence and improvement of a high-precision reference voltage in a DA conversion circuit, which is applicable to ADC, DAC and other analog conversion circuits, and particularly applicable to circuit design and application using the reference voltage as a reference. Background Art

[0002] The reference voltage generally refers to a known and stable voltage, which can be used to measure the relevant voltage in the circuit or conduct voltage comparison, and is commonly used as a reference for other voltages or a reference basis for conversion. Therefore, the reference voltage must have good stability and high precision. In the design and application of ADC, DAC and other analog circuits, the precision of the reference voltage often determines the precision of the output signal.

[0003] The technology of high-precision reference voltage and related chips have been very mature, and it is widely used in ADC and DAC conversion circuits based on the reference voltage value as the calculation reference input. In applications, we often use the default output of the reference voltage chip or the output after adjusting the gain / balance as the reference voltage for the operation of the backend chip. In actual design, in order to facilitate debugging, measurement or matching, some resistors and capacitors are usually reserved in the design. However, these seemingly insignificant devices with small resistance and small capacitance always bring unexpected effects, such as causing deviation of the reference voltage reaching the DAC conversion, resulting in deviation of the output precision, and the greater the precision deviation, the greater the error of the DAC conversion result.

[0004] The Chinese utility model patent with the publication number of CN107979892A, which was publicly disclosed on May 1, 2018, discloses a reference voltage control circuit, a control method and a ripple elimination circuit applying the same. The Chinese utility model patent with the publication number of CN208351358U, which was publicly disclosed on January 8, 2019, discloses a trimming circuit for a high-precision reference voltage. Both of the above two patents mention the importance of the reference voltage in circuit applications, and how to adjust and compensate the circuit generating the reference voltage to achieve the purpose of minimizing the ripple of the reference voltage and improving the output precision of the reference voltage. However, neither of the above two patents involves how to design the circuit to ensure the precision and stability of the reference voltage during the whole use process when the output precision of the reference voltage is high enough and the ripple is small enough in actual circuit applications. Summary of the Utility Model

[0005] The technical problem to be solved by the utility model is: in actual circuit applications, how to design the circuit to ensure the precision and stability of the reference voltage during the whole use process when the output precision of the reference voltage is high enough and the ripple is small enough.

[0006] To solve the above technical problems, the technical solution of the present utility model is to provide a DA conversion circuit with a high-precision reference voltage, including a high-precision reference voltage chip of model SW688 and a digital-to-analog conversion chip of model SDA8412, wherein:

[0007] The 12th pin and the 5th pin of the high-precision reference voltage chip are respectively connected to the control ends of the adjusting resistor R3 and the adjusting resistor R4; one end of the adjusting resistor R3 is connected to the 6th pin, the 4th pin of the high-precision reference voltage chip and one end of the adjusting resistor R4, and the 6th pin and the 4th pin of the high-precision reference voltage chip are also connected in series with a resistor R5 and then connected to the voltage source; the other end of the adjusting resistor R3 is connected to the 8th pin, the 13th pin of the high-precision reference voltage chip and the other end of the adjusting resistor R4; the 7th pin of the high-precision reference voltage chip is connected to the ground after being connected in series with a capacitor C1; the 3rd pin of the high-precision reference voltage chip is connected to the VREFH end of the digital-to-analog conversion chip; the 14th pin of the high-precision reference voltage chip is connected to the VREFL end of the digital-to-analog conversion chip, and its characteristics are:

[0008] The 1st pin of the high-precision reference voltage chip is directly connected to the VREFH end of the digital-to-analog conversion chip without passing through any series resistors; the 15th pin of the high-precision reference voltage chip is directly connected to the VREFL end of the digital-to-analog conversion chip without passing through any series resistors.

[0009] Preferably, one end of the capacitor C2 is connected to the 1st pin of the high-precision reference voltage chip and the VREFH end of the digital-to-analog conversion chip, and the other end is grounded.

[0010] Preferably, one end of the capacitor C3 is connected to the 15th pin of the high-precision reference voltage chip and the VREFL end of the digital-to-analog conversion chip, and the other end is grounded.

[0011] Compared with the prior art solution, the present utility model has the following beneficial effects:

[0012] 1) For the modules that have been designed and produced, the reference voltage accuracy can be adjusted by modifying the series resistors, avoiding ineffective re-design changes, or relying on external resistor adjustment to correct the instability caused by environmental factor changes in the reference voltage output.

[0013] 2) Generally, the current of the reference voltage is relatively small and the accuracy requirement is relatively high. Therefore, resistors should not be connected in series on the circuit as much as possible. The analysis method and design of this problem can be extended to other similar circuit designs using the reference voltage. Description of the Drawings

[0014] Figure 1 It is the circuit design block diagram before the improvement of the present utility model. In the figure, ①, ③, ④, ⑤, ⑥, ⑦, ⑧, They are the 1st, 3rd, 4th, 5th, 6th, 7th, 8th, 12th, 13th, 14th, and 15th pins of the high-precision reference voltage chip with the model number SW688 respectively;

[0015] Figure 2 This is the improved circuit design block diagram of the present invention. Specific embodiments

[0016] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0017] As Figure 1 shown, the main chips of the DA conversion circuit of the present invention are the high-precision reference voltage chip with the model number SW688 (hereinafter referred to as "SW688") and the digital-to-analog conversion chip with the model number SDA8412 (hereinafter referred to as "SDA8412"). On this platform, the present invention analyzes the reasons for the large deviation between the actual measured values and the calculated values of the four-way analog outputs of the digital-to-analog conversion chip and seeks solutions to the problems.

[0018] SW688 is a precision ±10V voltage reference chip manufactured by bipolar process, providing a precision ±10V voltage reference for the conversion of the digital-to-analog conversion chip. This high-precision reference voltage chip has the following characteristics:

[0019] 1) Positive and negative reference outputs: ±10V;

[0020] 2) High output voltage accuracy: ±10mV (at room temperature);

[0021] 3) Good temperature coefficient: 15ppm / °C;

[0022] 4) With internal Kelvin connection function;

[0023] 5) Voltage regulation rate ≤ ±200μV / V;

[0024] 6) Output current ±10mA;

[0025] 7) The gain of the 5th pin of the chip mainly finely tunes the 10V output voltage;

[0026] 8) The balance of the 12th pin of the chip mainly finely tunes the -10V output voltage.

[0027] SDA8412 is a four-channel 12-bit D / A converter, and the chip internally contains four functionally independent D / A converters. When using VDD = 15V, V SS = -15V, V REFH = 10V, V REFL When = -10V, the voltage range of the four-way output is: -10V to 10V. This is also the voltage configuration used in the embodiments of the present invention.

[0028] For the convenience of adjustment and testing, a 10Ω resistor R1 and R2 are connected in series on the VREFH and VREFL ± reference voltage power supply lines of SW688 and SDA8412. The adjustment resistors R3 and R4 connected to the 5th pin (GAIN terminal) and the 12th pin (B LANCE terminal) of the SW688 chip are in a suspended default configuration state, and the reference voltage output completed by the internal configuration of the chip is used. After the module is powered on, the measured VREFH = 10.0021V and VREFL = -10.0011V, and the voltage fully meets the requirement of the output accuracy of ±10mV of SW688. After the program is loaded, the output voltage of SDA8412 is measured.

[0029] According to the SDA8412 calculation formula The theoretical value V REFH = 10.0000V, V REFL = -10.0000V. When N selects different data (N is an integer, and the value range is 0 to 4095), different output voltages will be generated. The following takes N = 0, 1024, 3072, and 4095 as examples for measurement, and the calculated values and actual measured values are as follows:

[0030] Serial number N Theoretical calculated value (V) Actual measured value (V) 1 0 -10.0000 -9.9015 2 1024 -5.0000 -4.9507 3 3072 5.0000 4.9510 4 4095 9.9951 9.8970

[0031] It can be seen from the above table that there is still a large error between the theoretical calculated value and the actual measured value of the output voltage. When analyzing the reasons for the error, it is found that before the system program is loaded, VREFH = 10.0021V and VREFL = -10.0011V. However, when the program is loaded, both VREFH and VREFL measured at the input of SDA841 have changed, VREFH = 9.9018V and VREFL = -9.9015V. The reasons for the voltage change are analyzed separately.

[0032] The analysis is carried out in three steps:

[0033] Step 1) After the program is loaded, in order to make VREFH and VREFL of SDA8412 as accurate as possible to ±10V, the gain of the 5th pin and the balance of the 12th pin of SW688 are finely tuned using external resistors. Initially, the output voltage accuracy of SDA8412 basically meets the requirements. However, as the working time increases and the ambient temperature changes, the output ripple at the same point begins to increase, and the output accuracy deteriorates. At this time, the tracked VREFH and VREFL fluctuate, the ripple also begins to increase, and the accuracy deteriorates. This calibration method is relatively susceptible to the environment, so it is generally not recommended to use the method of external resistor gain and balance for precision adjustment, especially in high-precision applications.

[0034] Step 2) Further analyze the reasons for the deterioration of the reference voltage accuracy. It is speculated that the resistors connected in series on the VREFH and VREFL links may affect the reference voltage: the maximum current of SW688 is ±10mA, and the current series resistor value is 10Ω ± 1%. According to V = IR, the maximum voltage drop on the line will be 0.10V, so the actual VREFH and VREFL reaching the input end of SDA8412 will shift. According to the theoretical value calculation, VREFH of SW688 = 10.000V, VREFL = -10.000V, then the measured VREFH = 9.900V and VREFL = -9.900V at the SDA8412 end. If ±9.900V is used as the reference value for calculation, the following results can be obtained:

[0035] Serial number N Theoretical calculated value (V) Actual measured value (V) 1 0 -9.9000 -9.9015 2 1024 -4.9500 -4.9507 3 3072 4.9500 4.9510 4 4095 9.8952 9.8970

[0036] The results show that without considering the voltage drop caused by the series resistor, the error between the theoretical calculation value and the actual measurement value is less than 0.002V, which is consistent with the accuracy error caused by resistor loss in the theoretical calculation. Further verification is carried out.

[0037] Step 3) Replace both resistors R1 and R2 with 0Ω precision resistors and measure again. The results of multiple measurements show that before and after the system is loaded, VREFH = 10.0011V and VREFL = -10.0012V, both remain stable, the ripple is stable, and does not change with the environment and working time. The corresponding output voltage measurements are as follows:

[0038] Serial number N Theoretical calculated value (V) Actual measured value (V) 1 0 -10.0000 -10.0010 2 1024 -5.0000 -5.0005 3 3072 5.0000 5.0006 4 4095 9.9951 9.9962

[0039] The test results show that the measurement error between the theoretical calculation value and the actual measurement value is further reduced, proving that the analysis and modification are effective. The improved circuit is as Figure 2 shown.

[0040] Verify by adopting the same processing method for multiple modules (by default, the adjustment resistors at the GAIN terminal and the BLANCE terminal are NC, and R1 and R2 are 0Ω). The output errors can all be controlled within 0.0011V, meeting the design requirements for accuracy.

Claims

1. A DA conversion circuit with a high-precision reference voltage, comprising a high-precision reference voltage chip of model SW688 and a digital-to-analog conversion chip of model SDA8412, wherein: The 12th pin and the 5th pin of the high-precision reference voltage chip are respectively connected to the control ends of the adjusting resistors R3 and R4; one end of the adjusting resistor R3 is connected to the 6th pin, the 4th pin of the high-precision reference voltage chip and one end of the adjusting resistor R4, and the 6th pin and the 4th pin of the high-precision reference voltage chip are also connected to the voltage source after being serially connected with the resistor R5; the other end of the adjusting resistor R3 is connected to the 8th pin, the 13th pin of the high-precision reference voltage chip and the other end of the adjusting resistor R4; the 7th pin of the high-precision reference voltage chip is grounded after being serially connected with the capacitor C1; The 3rd pin of the high-precision reference voltage chip is connected to the VREFH end of the digital-to-analog conversion chip; the 14th pin of the high-precision reference voltage chip is connected to the VREFL end of the digital-to-analog conversion chip, and it is characterized in that: The 1st pin of the high-precision reference voltage chip is directly connected to the VREFH end of the digital-to-analog conversion chip without passing through any serially connected resistors; the 15th pin of the high-precision reference voltage chip is directly connected to the VREFL end of the digital-to-analog conversion chip without passing through any serially connected resistors.

2. The DA conversion circuit with a high-precision reference voltage according to claim 1, characterized in that One end of the capacitor C2 is connected to the 1st pin of the high-precision reference voltage chip and the VREFH end of the digital-to-analog conversion chip, and the other end is grounded.

3. The DA conversion circuit with a high-precision reference voltage as described in claim 1, characterized in that, One end of the capacitor C3 is connected to the 15th pin of the high-precision reference voltage chip and the VREFL end of the digital-to-analog conversion chip, and the other end is grounded.

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