SBAA631 January   2025 DAC80508 , INA592 , XTR111 , XTR300 , XTR305

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Analog Output Module Specification
  6. 3Analog Output Module Structure
  7. 4Multi-Channel Output Architectures
    1. 4.1 Fully Integrated DAC Architecture
    2. 4.2 Low Voltage DAC Plus an Output Buffer
    3. 4.3 Track and Hold Multiplexed Output
  8. 5Single-Channel Output Architectures
    1. 5.1 Fully Integrated DAC
    2. 5.2 Low-Voltage DAC Plus an Output Buffer
    3. 5.3 Pulse-Width Modulation Plus a Buffer
  9. 6Output Buffers
    1. 6.1 Unidirectional Current Buffer
    2. 6.2 Bidirectional Current Buffer
    3. 6.3 Voltage Buffer
    4. 6.4 Combined Voltage or Current Buffer
  10. 7Summary
  11. 8References

6.2 Bidirectional Current Buffer

Bidirectional current output is less common for AOUT modules. When a bidirectional current output is required, a modified Howland circuit is used.

An integrated difference amplifier implementation like INA592 provides resistor matching for high output accuracy, and requires only one external precision resistor. The amplifier has extremely low offset in the uV range, and has relatively high bandwidth of 2MHz. Check High-side current sources for industrial applications for more details.

Bidirectional Current Buffer Bidirectional Current BufferFigure 6-2 Bidirectional Current Buffer

The difference amplifier can also be built discrete using op amps like OPA196, this however needs precisely matched resistors to achieve a reasonable accuracy.

In both implementations, in addition to the voltage input, a reference input in the middle of the input range is needed to generate the bidirectional current. More details about this design can be found in Analysis of Improved Howland Current Pump Configurations.