SBOSA51 December   2020 THS4567

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics: Differential TIA Mode, ICM loop enabled
    6. 6.6 Electrical Characteristics: FDA operation, ICM loop disabled
    7. 6.7 Typical Characteristics: (VS+) – (VS–) = 5 V
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Main Amplifier
      2. 7.3.2 Output Common-Mode Control
      3. 7.3.3 Input Common-Mode Control
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Differential Transimpedance Amplifier Mode
      3. 7.4.3 Fully Differential Amplifier (FDA) Mode
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Noise Analysis
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure (THS4567 in TIA Mode)
        1. 8.2.2.1 OPA Mode Configuration
      3. 8.2.3 Application Curves
    3. 8.3 Differential TIA with 0-V Biased Photodiode
    4. 8.4 Differential AC Coupled TIA
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Board Layout Recommendations
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Documentation Support
      1. 11.1.1 Related Documentation
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Support Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.2.3 Application Curves

Figure 8-5 shows the output of the THS4567 device in TIA mode. The output common-mode is centered on VOCM = 2.5 V and the differential output of 10 VPP maximizes the subsequent ADCs entire common-mode range.

Figure 8-6 shows the output of the first stage transimpedance amplifier setup shown in Figure 8-3. The output common-mode is centered on 0.83 V. The offset in the common-mode is caused by the offset due to the ambient light. More importantly the differential output swing is only 3.33 V. To maximize the ADC dynamic range the subsequent THS4561 differential amplifier stage is configured in a signal gain of 3 V/V. The THS4561 device will also perform a level shift to center the output common-mode to 2.5 V.

GUID-20201110-CA0I-8KFK-TTRW-TMNDH3VHCH8V-low.gifFigure 8-5 Output of THS4567 (TIA Mode)
GUID-D100E74B-ED73-42DE-B4B0-FCC2987E29F6-low.gifFigure 8-6 Output of the 1st Stage Discrete Op Amp Transimpedance Amplifier (OPA Mode)

The noise performance of the THS4567 device (half-circuit) is then compared against the noise of the OPA607 and the OPA365 in OPA mode. Using Equation 1 we can estimate the total input referred spot noise for the THS4567 device. Transimpedance Considerations for High-Speed Amplifiers is used to estimate the noise of the OPA607 and OPA365 transimpedance amplifier stage in OPA mode.

A PD capacitance of 5 pF is assumed. In a real world system the PD capacitance will be higher in OPA mode because of the lower reverse bias across the PD. The calculated noise results are shown in Table 8-1 where the benefit of the THS4567 device can clearly be seen. The spot noise has been normalized to the closed loop bandwidth. The OPA mode architecture would require a second gain stage to maximize the ADCs input full scale range. The second stage would increase the power consumption and degrade the noise.

Table 8-1 Noise Comparison
Amplifier SpecificationTHS4567OPA607OPA365
Photodiode Capacitance (pF)555
Amplifier Input Capacitance (pF)1178
Amplifier Voltage Noise (nV/√ Hz)4.23.84.5
TIA Gain (kΩ)1000333.33333.33
Closed Loop Bandwidth (MHz)2.411.4
Input-Referred Spot Noise (pA/√ Hz)0.20.390.36