SBAA532A February   2022  – March 2024 ADS1119 , ADS1120 , ADS1120-Q1 , ADS112C04 , ADS112U04 , ADS1130 , ADS1131 , ADS114S06 , ADS114S06B , ADS114S08 , ADS114S08B , ADS1158 , ADS1219 , ADS1220 , ADS122C04 , ADS122U04 , ADS1230 , ADS1231 , ADS1232 , ADS1234 , ADS1235 , ADS1235-Q1 , ADS124S06 , ADS124S08 , ADS1250 , ADS1251 , ADS1252 , ADS1253 , ADS1254 , ADS1255 , ADS1256 , ADS1257 , ADS1258 , ADS1258-EP , ADS1259 , ADS1259-Q1 , ADS125H01 , ADS125H02 , ADS1260 , ADS1260-Q1 , ADS1261 , ADS1261-Q1 , ADS1262 , ADS1263 , ADS127L01 , ADS130E08 , ADS131A02 , ADS131A04 , ADS131E04 , ADS131E06 , ADS131E08 , ADS131E08S , ADS131M02 , ADS131M03 , ADS131M04 , ADS131M06 , ADS131M08

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Bridge Overview
  5. 2Bridge Construction
    1. 2.1 Active Elements in Bridge Topologies
      1. 2.1.1 Bridge With One Active Element
        1. 2.1.1.1 Reducing Non-Linearity in a Bridge With One Active Element Using Current Excitation
      2. 2.1.2 Bridge With Two Active Elements in Opposite Branches
        1. 2.1.2.1 Eliminating Non-Linearity in a Bridge With Two Active Elements in Opposite Branches Using Current Excitation
      3. 2.1.3 Bridge With Two Active Elements in the Same Branch
      4. 2.1.4 Bridge With Four Active Elements
    2. 2.2 Strain Gauge and Bridge Construction
  6. 3Bridge Connections
    1. 3.1 Ratiometric Measurements
    2. 3.2 Four-Wire Bridge
    3. 3.3 Six-Wire Bridge
  7. 4Electrical Characteristics of Bridge Measurements
    1. 4.1 Bridge Sensitivity
    2. 4.2 Bridge Resistance
    3. 4.3 Output Common-Mode Voltage
    4. 4.4 Offset Voltage
    5. 4.5 Full-Scale Error
    6. 4.6 Non-Linearity Error and Hysteresis
    7. 4.7 Drift
    8. 4.8 Creep and Creep Recovery
  8. 5Signal Chain Design Considerations
    1. 5.1 Amplification
      1. 5.1.1 Instrumentation Amplifier
        1. 5.1.1.1 INA Architecture and Operation
        2. 5.1.1.2 INA Error Sources
      2. 5.1.2 Integrated PGA
        1. 5.1.2.1 Integrated PGA Architecture and Operation
        2. 5.1.2.2 Benefits of Using an Integrated PGA
    2. 5.2 Noise
      1. 5.2.1 Noise in an ADC Data Sheet
      2. 5.2.2 Calculating NFC for a Bridge Measurement System
    3. 5.3 Channel Scan Time and Signal Bandwidth
      1. 5.3.1 Noise Performance
      2. 5.3.2 ADC Conversion Latency
      3. 5.3.3 Digital Filter Frequency Response
    4. 5.4 AC Excitation
    5. 5.5 Calibration
      1. 5.5.1 Offset Calibration
      2. 5.5.2 Gain Calibration
      3. 5.5.3 Calibration Example
  9. 6Bridge Measurement Circuits
    1. 6.1 Four-Wire Resistive Bridge Measurement with a Ratiometric Reference and a Unipolar, Low-Voltage (≤5 V) Excitation Source
      1. 6.1.1 Schematic
      2. 6.1.2 Pros and Cons
      3. 6.1.3 Parameters and Variables
      4. 6.1.4 Design Notes
      5. 6.1.5 Measurement Conversion
      6. 6.1.6 Generic Register Settings
    2. 6.2 Six-Wire Resistive Bridge Measurement With a Ratiometric Reference and a Unipolar, Low-Voltage (≤ 5 V) Excitation Source
      1. 6.2.1 Schematic
      2. 6.2.2 Pros and Cons
      3. 6.2.3 Parameters and Variables
      4. 6.2.4 Design Notes
      5. 6.2.5 Measurement Conversion
      6. 6.2.6 Generic Register Settings
    3. 6.3 Four-Wire Resistive Bridge Measurement With a Pseudo-Ratiometric Reference and a Unipolar, High-Voltage (> 5 V) Excitation Source
      1. 6.3.1 Schematic
      2. 6.3.2 Pros and Cons
      3. 6.3.3 Parameters and Variables
      4. 6.3.4 Design Notes
      5. 6.3.5 Measurement Conversion
      6. 6.3.6 Generic Register Settings
    4. 6.4 Four-Wire Resistive Bridge Measurement with a Pseudo-Ratiometric Reference and Asymmetric, High-Voltage (> 5 V) Excitation Source
      1. 6.4.1 Schematic
      2. 6.4.2 Pros and Cons
      3. 6.4.3 Parameters and Variables
      4. 6.4.4 Design Notes
      5. 6.4.5 Measurement Conversion
      6. 6.4.6 Generic Register Settings
    5. 6.5 Four-Wire Resistive Bridge Measurement With a Ratiometric Reference and Current Excitation
      1. 6.5.1 Schematic
      2. 6.5.2 Pros and Cons
      3. 6.5.3 Parameters and Variables
      4. 6.5.4 Design Notes
      5. 6.5.5 Measurement Conversion
      6. 6.5.6 Generic Register Settings
    6. 6.6 Measuring Multiple Four-Wire Resistive Bridges in Series with a Pseudo-Ratiometric Reference and a Unipolar, Low-Voltage (≤5V) Excitation Source
      1. 6.6.1 Schematic
      2. 6.6.2 Pros and Cons
      3. 6.6.3 Parameters and Variables
      4. 6.6.4 Design Notes
      5. 6.6.5 Measurement Conversion
      6. 6.6.6 Generic Register Settings
    7. 6.7 Measuring Multiple Four-Wire Resistive Bridges in Parallel Using a Single-Channel ADC With a Ratiometric Reference and a Unipolar, Low-Voltage (≤ 5 V) Excitation Source
      1. 6.7.1 Schematic
      2. 6.7.2 Pros and Cons
      3. 6.7.3 Parameters and Variables
      4. 6.7.4 Design Notes
      5. 6.7.5 Measurement Conversion
      6. 6.7.6 Generic Register Settings
    8. 6.8 Measuring Multiple Four-Wire Resistive Bridges in Parallel Using a Multichannel ADC With a Ratiometric Reference and a Unipolar, Low-Voltage (≤ 5 V) Excitation Source
      1. 6.8.1 Schematic
      2. 6.8.2 Pros and Cons
      3. 6.8.3 Parameters and Variables
      4. 6.8.4 Design Notes
      5. 6.8.5 Measurement Conversion
      6. 6.8.6 Generic Register Settings
  10. 7Summary
  11. 8Revision History

6.5.3 Parameters and Variables

Table 6-18 defines important parameters and Table 6-19 provides equations for different variables. These parameters and variables are specific to this bridge configuration.

Table 6-10 User-Defined System Parameters
ParameterDescription
IIDACBridge excitation current
RBRIDGENominal bridge impedance
RBIASBias resistor between the VEXCITATION– and ground (can be removed under certain conditions)
VCM(ADC)Target common-mode voltage for inputs to the ADC (typically AVDD / 2)
Bridge SensitivityChange in bridge output voltage relative to excitation voltage
Load(Bridge Max)Maximum load that can be applied to the bridge
Load(System Max)Maximum load applied to the bridge in the system (can be ≤ Load(Bridge Max))
Table 6-11 Variable Equations and Definitions
VariableEquationDescription
RTOTALRBRIDGE + RBIASTotal resistance seen between IDAC pin and ground
VBRIDGEIIDAC • RBRIDGEVoltage across the bridge
VREFVEXCITATION+ - VEXCITATION–Differential reference voltage to the ADC
VCOMPLIANCEIIDAC • RTOTALMaximum voltage that can be applied to the IDAC pin to maintain constant current
VCM(Bridge)VBRIDGE / 2 + VBIASBridge output common-mode voltage
VOUT(Bridge Max)VBRIDGE • Bridge SensitivityMaximum differential output voltage of the bridge
VOUT(System Max)(VOUT(Bridge Max) • Load(System Max)) / Load(Bridge Max)Maximum differential bridge output voltage used in the system
(can be ≤ VOUT(System Max))
VINVSIGNAL+ – VSIGNAL–Differential input voltage to the ADC