1Terms and Definitions
| afGydF4y2Ba | Analog front end |
| 我知道了GydF4y2Ba | Integrated circuit |
| opamp.GydF4y2Ba | 运算放大器GydF4y2Ba |
| R.H | Digital rheostat |
2R.eferences
对于相关的文件和软件，请访问：GydF4y2Ba
//www.xmece.com/products/greenpak/analog-greenpaks
下载我们的FreeGreenPak Designer软件[1]打开.gp文件[2]并查看所提出的电路设计。使用GreenPak开发工具[3]在几分钟内将设计冻结到您自己的定制IC中。yabo国际娱乐对话框半导体提供完整的应用程序库注意[4]，其中包含了设计示例以及对话框IC中的功能和块的说明。GydF4y2Ba
- GreenPAK Designer Software，软件下载和用户指南，对话框半导体yabo国际娱乐GydF4y2Ba
- 压力传感器的AN-CM-308模拟前端.GPGydF4y2Ba，GreenPak设计文件，对话半导体yabo国际娱乐GydF4y2Ba
- GreenPAK Development Tools那GreenPAK Development Tools Webpage, Dialog Semiconductor
- GreenPak应用笔记GydF4y2Ba那GreenPak应用笔记Webpage, Dialog Semiconductor
- SLG47004，数据表，对话半导体yabo国际娱乐GydF4y2Ba
作者：vladyslav kozlovGydF4y2Ba
3 Introduction
In the following application note the SLG47004 is used as the analog front-end (AFE) for a Wheatstone bridge pressure sensor. Two configurable OpAmps and one internal OpAmp, all within the SLG47004 are used to create an instrumentation amplifier. Digital rheostats RH0 and RH1 of the SLG47004 are used to tune the gain of the AFE and to compensate offset voltages of sensor and OpAmps. Also, the trim procedure helps to minimize an error caused by mismatch between external resistors. The Auto-Trim function of the SLG47004 simplifies the process of gain tuning and offset compensation and allows saving hardware resources, as well as minimize the cost of the AFE.
SLG47004允许两种不同的方式与内部参考源有和没有内部参考源的addcs：GydF4y2Ba
- In the case when an external ADC has a separate analog reference pin, the common way is to supply all analog blocks (sensor, ADC, DAC for compensating offset) from one voltage source. The measurements are ratiometric. Variations in supply voltage don’t affect accuracy.
- In the case when an ADC has an internal reference source only, the supply voltage for the sensor and DAC must be stable and constant. That’s why, for this case, an internal buffered Vref of the SLG47004 must be used.
4 AFE没有内部电压参考源GydF4y2Ba
4.1 Hardware Setup of AFE Without Internal Voltage Reference
Figure 1 shows a schematic of the analog front end for MCU with ADC, which has an external analog reference option. Sensor, ADC reference, DAC (Rdiv1, RH0, Rdiv2 divider for offset compensation), and Chopper ACMP reference are powered from one voltage source: Van. Characteristics of the components can be found in Table 1. A pressure sensor from Honeywell (NSCSDRN060MD) is used in this example.
Figure 1: Analog Front-End for a Wheatstone Bridge Sensor
In Figure 1 V一个GydF4y2Ba是模拟组件的电源电压。V.GydF4y2Ba一个GydF4y2Bais filtered VDD.GydF4y2Ba电压。没有压力的传感器的输出等于（vGydF4y2Ba一个GydF4y2Ba/ 2±vGydF4y2Baos_Bridge.GydF4y2Ba），其中vGydF4y2Baos_Bridge.GydF4y2Ba是桥梁偏移电压。由于可以在两个方向上施加传感器的力，因此传感器的输出可以高于或低于零点（VGydF4y2Ba一个GydF4y2Ba/ 2±vGydF4y2Baos_Bridge.GydF4y2Ba). So the AFE must amplify the output signal differentially between the sensor zero point and its actual output.
The optional CFGydF4y2Ba需要电容来取消数字变阻器的开关噪声。c的值GydF4y2BaFGydF4y2Bacan be changed.
The output voltage of AFE is:
where
R.FGydF4y2Ba- 是用户定义的电阻，GydF4y2BaR.FGydF4y2Ba当前项目中的200kΩ和0.5％的耐受性;GydF4y2Ba
R.GGydF4y2Ba– is user-defined gain resistor;
V.GydF4y2Ba裁判GydF4y2Ba-is the reference voltage for the instrumentation amplifier.
4.2 Precision Characteristics of Components
Precision characteristics of the components are shown in Table 1.
范围GydF4y2Ba |
Description |
V.alue |
Unit |
|---|---|---|---|
Sensor Characteristics |
|||
ΔP |
压力范围GydF4y2Ba |
±6.0 |
KPA.GydF4y2Ba |
K.V.GydF4y2Baout |
Full Scale Span Coefficient |
±2.46（min），±2.60（典型值），±2.8（最多）GydF4y2Ba |
mV/V |
K.GydF4y2Baos_out |
null偏移系数GydF4y2Ba |
±0.075 |
mV/V |
3.3 V DC的传感器特性GydF4y2Ba |
|||
ΔVout |
输出电压跨度GydF4y2Ba |
±8.1 (min), ±8.58 (typ), ±9.2 (max) |
mV |
V.GydF4y2Baos_Bridge.GydF4y2Ba |
Null Offset |
±0.248 (max) |
mV |
DV.GydF4y2Baos_Bridge.GydF4y2Ba/ dt.GydF4y2Ba |
Offset Temperature Drift (T = 0 to 50 °C) |
±0.6 (max) |
％FSS |
opamp.s Characteristics |
|||
V.GydF4y2Baosopamp.GydF4y2Ba |
输入偏移电压GydF4y2Ba |
1。0 (max) |
mV |
DV.GydF4y2Baosopamp.GydF4y2Ba/ dt.GydF4y2Ba |
用温度偏移漂移GydF4y2Ba |
5（最大）GydF4y2Ba |
µV/°C |
ΔR㈡GydF4y2Ba |
Mismatch Between Internal R1, R2, R3, R4 Resistors |
0.05GydF4y2Ba |
％GydF4y2Ba |
Digital Rheostats Characteristics |
|||
R.H1, RH2 |
数字变温岩抵抗GydF4y2Ba |
80 (min), 100 (typ), 120 (max) |
kOhm |
NGydF4y2Ba点击GydF4y2Ba |
Number of Taps |
1024.GydF4y2Ba |
|
FGydF4y2Bachacmp.GydF4y2Ba |
斩波比较器开关频率GydF4y2Ba |
10 |
kHz |
V.GydF4y2Bach_offset.GydF4y2Ba |
Chopper Comparator Offset when Set is Active |
300 (max) |
µV |
DNL.GydF4y2Ba |
Differential Non-Linearity (max) |
1GydF4y2Ba |
LSB.GydF4y2Ba |
αR(T) |
Nominal Resistance Temp Coefficient |
100 |
PPM /°CGydF4y2Ba |
高清缓冲器特性GydF4y2Ba |
|||
V.GydF4y2Baos_HD_Buf |
HD缓冲偏移GydF4y2Ba |
±3 (max), T = 25 °C |
mV |
ΔVOUT(I) |
HD Buffer Load Regulation at I加载GydF4y2Ba= 2mA |
2GydF4y2Ba |
mV |
外部电阻特性GydF4y2Ba |
|||
ΔRext |
电阻容差GydF4y2Ba |
0.5和1GydF4y2Ba |
％GydF4y2Ba |
αRext（t）GydF4y2Ba |
电阻温度系数GydF4y2Ba |
50 |
PPM /°CGydF4y2Ba |
4.3 Internal GreenPAK Design and Macrocells Configurations
4.3.1 Internal Design of the Project
Figure 2 shows the internal design of the project in GreenPAK Designer Software.
4.3.2 opamps配置GydF4y2Ba
opamps配置如图3所示。GydF4y2Ba
Figure 3: OpAmps Configurations
4.3.3斩波器ACMP配置GydF4y2Ba
Channel0 of Chopper ACMP is used for offset correction. Channel1 of Chopper ACMP is used for tuning gain of AFE. Chopper ACMP configuration is shown in Figure 4.
Figure 4: Chopper ACMP Configuration
4.3.4数字变阻器配置GydF4y2Ba
Digital Rheostats configurations are shown in Figure 5.
Figure 5: Digital Rheostats Configurations
4.3.5 LUT Configuration
LUT configuration is shown in Figure 6.
4.3.6 Temperature Sensor Configuration
The temperature sensor configuration is shown in Figure 7.
Figure 7: Temperature Sensor Configuration
4.3.7 Oscillator0 and I²C Macrocells Configurations
Oscillator0 and I²C Macrocells use default configurations.
4.3.8 GPIOs Configurations
GPIOs configurations are shown in Figure 8.
Figure 8: GPIOs Configurations
4.4 Gain Resistor Calculation
为了计算增益电阻器RG的值，必须评估仪表放大器的最小和最大增益。考虑传感器V的可能输出跨度GydF4y2Ba一个GydF4y2Ba·kv.GydF4y2Baout(from 8.12 mV to 9.24 mV for V一个GydF4y2Ba= 3.3 V），可以从等式中找到AFE的增益：GydF4y2Ba
where获得_ref_ChopACMP- 是CoppperAcMP的参考电压，用于增益调谐（参见Channper1的Channer1参考源，第4.3.3节）。GydF4y2Ba获得_ref_ChopACMP= V达达GydF4y2Ba*(3/64) or 0.155 V for V一个GydF4y2Ba= 3.3 V.GydF4y2Ba
对于图1V所示的示意图GydF4y2Ba达达GydF4y2Ba= V一个GydF4y2Ba。因此，可以将等式（2）重写为GydF4y2Ba
or
From equation (3) it’s seen that variations in V一个GydF4y2Ba电压不会影响系统的增益：GydF4y2Ba
Now it’s possible to build the graph for the function Gain = f(n), where n – is the code of the rheostat from 1 to 1024:
Note that the chip to chip variation of RH maximum resistance is from 80 kΩ to 120 kΩ. The 80 kΩ value should be used for gain resistor calculation.
By varying the value of RGGydF4y2Bait’s possible to match the span of AFE gain from Gain_min to Gain_max, see Figure 9. If there is no RGGydF4y2Bavalue to match the desired range, then RFGydF4y2Ba值应该增加。对于当前的示意图GydF4y2BaFGydF4y2Ba= 200 kΩ and RGGydF4y2Ba= 2.61 kΩ.
图9：AFE的增益作为数字变阻器代码的函数，rgain = f（n）GydF4y2Ba
4.5 VREF分频器电阻计算GydF4y2Ba
计算DAC电阻的值（RDIV1，RH0，RDIV2分频器）的最大范围（VGydF4y2Bacompvalue) should be calculated. Considering the biggest possible gain of the AFE (Gain_max = 184.2) and the biggest possible input offset (see Figure 10):
the Vref can be changed by the value of Vcomp：GydF4y2Ba
To find the value of Rdiv1, Rdiv2, the next equation system should be solved:
whereRH0.GydF4y2Bamax- 在最坏的情况下，变阻器的最大阻力GydF4y2BaRH0.GydF4y2Bamax=80kΩ;GydF4y2Ba
V.GydF4y2Ba一个GydF4y2Ba– is the voltage applied to the divider.
对于当前的示意图，最接近的电阻标准值GydF4y2BaR.GydF4y2Badiv2= 75 kΩ,R.GydF4y2Badiv1=46.4kΩ。GydF4y2Ba
4.6 Offset Error Sources and Offset Compensation
To set zero point for the AFE (zero pressure) the voltage from divider (Rdiv1, RH0, Rdiv2) is used. The output from the divider must be connected to the instrumentation amplifier through the buffer to eliminate the impact of DAC output resistance.
通过改变RH0的值不仅是传感器偏移，而且可以补偿opamps输入偏移电压。请参阅下面的等式。GydF4y2Ba
让我们向等式添加偏移电压（1）：GydF4y2Ba
whereV.GydF4y2Baosopamp.0那GydF4y2BaV.GydF4y2Baosopamp.1GydF4y2Ba那GydF4y2BaV.GydF4y2Baos_intopamp.GydF4y2Ba- 是SLG47004放大器的输入偏移电压;GydF4y2Ba
V.GydF4y2Baos_input_buffer.GydF4y2Ba– is buffer input offset voltage;
V.GydF4y2Baosbridge- 是传感器的偏移电压;GydF4y2Ba
vcm_error.GydF4y2Ba- 是由内部R1，R2，R3，R4电阻和外部R引起的共模电压误差引起的GydF4y2BaFGydF4y2Baresistors. This voltage will be compensated after the trim procedure.
V.GydF4y2Bacomp– is the shift voltage from the divider for offset voltages compensation.
请注意，选择偏移电压的迹象以显示最坏情况的错误，请参见图10。GydF4y2Ba
图10：带有偏移源的AFE，以显示最坏的情况GydF4y2Ba
4.7 AFE的调整增益GydF4y2Ba
由于传感器跨度的范围为±8.1 mV至±9.2 mV for V.GydF4y2Ba一个GydF4y2Ba= 3.3 V，必须调整仪表放大器的增益以覆盖AFE的完整输出范围。GydF4y2Ba
SLG47004 Opamps的线性输出摆动来自GND + 100 MV到V.GydF4y2BaDD.GydF4y2Ba-100 mV. It’s proposed to use the output range from V达达GydF4y2Ba*(32/64) to (V达达GydF4y2Ba- V.GydF4y2Ba达达GydF4y2Ba*（3/64））用于正传感器输出和V.GydF4y2Ba达达GydF4y2Ba*(32/64) to V达达GydF4y2Ba*（3/64）用于负传感器输出。V.GydF4y2Ba达达GydF4y2Ba*（3/64）是内部斩波器ACMP的阈值，用于增益调谐。V.GydF4y2Ba达达GydF4y2Ba*（3/64）= V的0.155 VGydF4y2Ba达达GydF4y2Ba= 3.3 V.GydF4y2Ba
4.8 Algorithm for Tuning Gain and Compensating Offset of the System
The initial value of RH0 and RH1 are 100 KΩ (80 KΩ in the worst case), code = 1024.
- 1st step: offset compensation. Load the sensor with zero load (no load). Send to the SLG47004 I²C command to set the V爱好者GydF4y2BaINPUT0（PARULE到PT0块的SET0输入）到逻辑高电平。这将启动RH0的自动修剪过程。然后i²c主人应该清除vGydF4y2Ba爱好者GydF4y2BaInput0 of the SLG47004, which is connected to Set0 input. During the Auto-Trim procedure the SLG47004 changes the value of RH0 until the output voltage of AFE reaches V达达GydF4y2Ba/ 2。自动修剪过程结束后（PT块的空闲/无效输出的逻辑级别变高），系统已准备好下一步。GydF4y2Ba
- 2nd step: gain tuning. Load the sensor with a defined load. Send to the SLG47004 I²C command to set V爱好者GydF4y2BaInput1 (pulse to Set1 input of PT block) to logic High level. This will start the Auto-Trim procedure for RH1. Then I²C should clear the V爱好者GydF4y2BaInput1 of the SLG47004, which is connected to Set1 input. During this Auto-Trim procedure the SLG47004 changes the value of RH1 until the output voltage of AFE reaches (V达达GydF4y2Ba*（3/64））。自动修剪过程结束后（PT块的空闲/活动输出的逻辑级别变高），系统已准备好下一步。GydF4y2Ba
- 第三步：偏移补偿。此步骤与第1步相同。GydF4y2Ba
可选地，如果需要更高的精度，则用户可以在考虑以下限制的情况下添加更多的偏移/增益校准步骤：GydF4y2Ba
- The Auto-Trim procedures of total offset compensation and system gain error must be done iteratively starting and finishing with the total offset compensation.
- Total system offset (sensor offset + OpAmp1 offset + OpAmp2 offset) must not be greater than Vsensor_output_range.GydF4y2Ba/ 2。GydF4y2Ba
Expected Gain errors after each tuning iteration are shown in Table 2.
Table 2: Expected Gain of AFE during Auto-Trim Procedure
获得GydF4y2Ba |
获得错误，％GydF4y2Ba |
|
|---|---|---|
Etalon获得GydF4y2Ba |
174.2GydF4y2Ba |
-GydF4y2Ba |
1st iteration (offset trim, then gain tuning) |
170.9GydF4y2Ba |
1.89％GydF4y2Ba |
第二迭代（偏移修剪，然后增益调谐）GydF4y2Ba |
173.4GydF4y2Ba |
0.49% |
第3次迭代（偏移修剪，然后增益调谐）GydF4y2Ba |
174.4GydF4y2Ba |
0.09% |
After the 3rd iteration the gain error is associated with the step error of digital rheostat.
4.9 Offset Compensation Accuracy
假设自动修剪在温度= 25°C时完成。仪表放大器的增益为273.3，rh电阻为100kΩ，用于代码= 1024.表3示出了设定零点（偏移补偿）的精度。GydF4y2Ba
范围GydF4y2Ba |
V.alue, V |
输出传感器范围的％误差GydF4y2Ba |
|---|---|---|
Step near set point (Vout[NRH0.GydF4y2Ba] - V.GydF4y2Baout[NRH0.GydF4y2Ba-1]）（注1）GydF4y2Ba |
0.0006GydF4y2Ba |
0.04％GydF4y2Ba |
考虑变阻器DNL（注2）步骤附近的步骤GydF4y2Ba |
0.0012.GydF4y2Ba |
0.08％GydF4y2Ba |
Step error considering DNL and ACMP offset (Note 3) |
0.0015.GydF4y2Ba |
0.1％GydF4y2Ba |
注1.GydF4y2Ba自动修剪系统的最低可实现误差是一个修剪步骤（数字流变仪代码的±1，见图11）。GydF4y2Ba
笔记2GydF4y2Ba将“靠近设定点”值乘以（vGydF4y2Baout[N博士GydF4y2Ba] - V.GydF4y2Baout[N博士GydF4y2Ba-1]）到2（dnl误差）。GydF4y2Ba
注3.GydF4y2Ba将300μV的典型斩波器ACMP偏移量添加到先前值。GydF4y2Ba
In the case of 10-bit ADC, the maximum error of the trimmed system is:
请注意，此错误值与V无关GydF4y2Ba一个GydF4y2Ba电压。GydF4y2Ba
5带内部电压参考源的AFEGydF4y2Ba
5.1 Hardware Setup of AFE with Internal Voltage Reference
The SLG47004 allows powering all analog components of the AFE (sensor, DAC, and reference for Chopper ACMP) from an internal voltage source, see Figure 12. For this purpose, the SLG47004 has a special high drive buffer (HD Buffer macrocell).
Figure 12: Analog Front-End with Internal Voltage Reference
5.2传感器精度特性2.048 V电源电压GydF4y2Ba
Characteristics of the pressure sensor at 2.048 V supply voltage are shown in Table 4. All other precision characteristics from Table 1 remain unchanged.
范围GydF4y2Ba |
Description |
V.alue |
Unit |
|---|---|---|---|
ΔP |
压力范围GydF4y2Ba |
±6.0 |
KPA.GydF4y2Ba |
K.V.GydF4y2Baout |
输出电压跨度GydF4y2Ba |
±5.04 (min), ±5.32 (typ), ±5.73 (max) |
mV |
K.GydF4y2Baos_out |
Null Offset |
±0.154（最大）GydF4y2Ba |
mV |
DV.GydF4y2Baos_Bridge.GydF4y2Ba/ dt.GydF4y2Ba |
Offset Temperature Drift (T = 0 to 50 °C) |
±0.6 (max) |
％FSS |
5.3 Internal Macrocells Configurations
5.3.1 HD缓冲区和Opamp0 VREF配置GydF4y2Ba
The HD Buffer shares the voltage reference with OpAmp0 Macrocell. Note that Vref can be connected (or disconnected) to OpAmp0 or HD Buffer macrocells independently. The configurations of HD Buffer and OpAmp0 Vref are shown in Figure 13.
图13:OpAmp Vref和HD缓冲区配置GydF4y2Ba
5.3.2斩波器ACMP配置为2.048 V电压参考GydF4y2Ba
Chopper ACMP configuration is shown in Figure 14.
图14：带有2.048 V电压参考的AFE的斩波器ACMP配置GydF4y2Ba
5.4使用2.048 V电压参考的AFE增益电阻和DAC分频器计算GydF4y2Ba
考虑到传感器的输出跨度（从V的5.04 mV到5.73 mVGydF4y2Ba一个GydF4y2Ba= 2.048 V），AFE的输出电压范围必须是：GydF4y2Ba
Using equation (3),
获得resistor RGGydF4y2Ba=1.33kΩ，rGydF4y2BaFGydF4y2Ba=100kΩ。偏移补偿范围是vGydF4y2Bacomp= ±(177.9*0.00215) = 0.382 V. The divider resistorsR.GydF4y2Badiv1=21.3kΩ，GydF4y2BaR.GydF4y2Badiv2=46.4kΩ。HD缓冲液的偏移量为3 mV。GydF4y2Ba
6 Software Simulation and Hardware Prototype Testing
图15，图16，图17和图18显示了自动修剪过程。图15，图16和图17示出了当脉冲的脉冲的持续时间短于自动修剪过程的持续时间时，如图15所示。对于这种情况，自动修剪过程的停止条件在第二次之后在时钟输入的上升沿处于上/下输入的变化。请参阅数据表[5]以获取有关自动修剪进程的更多信息。GydF4y2Ba
如果用户在高电平下保持设置输入，则自动调整系统将继续操作，输出将遵循参考点，请参见图18。GydF4y2Ba
第一个自动修剪迭代的最大时间是RH_CODE / F.GydF4y2BaAuto-Trim= 511/2048 = 250毫秒。GydF4y2Ba
Figure 16: Software Simulation Results of Offset Correction Process, Enlarged
Figure 17: Auto-Trim Procedure with Short Pulse at Set Input of RH
图18：在RH的设置输入时具有长脉冲的自动修剪过程GydF4y2Ba
7结论GydF4y2Ba
The application note describes the design procedure of the analog front-end for a Wheatstone bridge pressure sensor. A unique Auto-Trim feature of the SLG47004 is used to compensate for the offset of operational amplifiers and sensor, and to tune the gain of the AFE.
它显示了如何计算增益和DAC电阻，以覆盖仪表放大器的全输出范围和全修整范围。GydF4y2Ba
达到最好的精度,建议use iterative procedures of offset compensation and then gain tuning. The first and last procedure should be offset compensation. Practical results show that the best precision is achieved after the 3rd iteration. For the sensor and AFE described in this application note, the gain and offset errors after the Auto-Trim procedures are ≈0.1% of the sensor range.