SLOSEB2 February   2026 VCA710

ADVANCE INFORMATION  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Thermal Information
    4. 5.4 Recommended Operating Conditions
    5. 5.5 Electrical Characteristics for LNA
    6. 5.6 Electrical Characteristics for VGA
    7. 5.7 Typical Characteristics: Low-Noise Amplifier (LNA)
    8. 5.8 Typical Characteristics: Variable Gain Amplifier (VGA)
    9. 5.9 Typical Characteristics: Low-Noise Amplifier + Variable Gain Amplifier
  7. 6 Parameter Measurement Information
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Device Functional Modes
  9. 8 Application and Implementation
    1. 8.1 Typical Application
      1. 8.1.1 Ultrasound Flow Meter Front-End
      2. 8.1.2 Design Requirements
      3. 8.1.3 Detailed Design Procedure
      4. 8.1.4 Optical Receiver Front-end
    2. 8.2 Power Supply Recommendations
    3. 8.3 Layout
      1. 8.3.1 Layout Guidelines
      2. 8.3.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 Device Support
    2. 9.2 Receiving Notification of Documentation Updates
    3. 9.3 Support Resources
    4. 9.4 Trademarks
    5. 9.5 Electrostatic Discharge Caution
    6. 9.6 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information
    1. 11.1 Tape and Reel Information
    2. 11.2 Mechanical Data

8.1.3 Detailed Design Procedure

The LNA sub-block inside the VCA710 supports both single ended and differential input. The ultrasound transducer can be connected either way as per the requirement to the input of the LNA. Beside providing a low input referred noise and an additional gain of 20dB, the LNA block also provides high input impedance making the part an excellent choice to be interfaced directly with high output impedance sensors.

Achieving an SNR of > 20dB is most challenging when the signal to the LNA is the lowest (100μVPP in this case). Since our frequency of interest is confined in and around 1MHz TI recommends adding an additional Band Pass Filter between the LNA and the VGA sub blocks. This limits the overall integrated noise carried forward towards the ADC. Refer to the application section of LOG300 8.2.1 Ultrasonic Distance Measurement for recommendation and design of a 1MHz band pass filter.

Assuming a bandpass filter of Pass Band frequency of 800kHz with a single pole roll of response, the overall integrated input referred noise of LNA is:

Equation 1. Vn (Input referred)=1nV/√Hz×√(800kHz ×1.57)
Equation 2. Vn=1.4µVrms
Equation 3. V n     p e a k   t o   p e a k = 6 × 1.4 µ V r m s = 8.4 µ V p p

The 4.5nV/√Hz input referred noise of the VGA sub-block translates to 0.45nV/√Hz at the input of LNA allowing us to conveniently ignore it in our calculation since its ~ 1/3rd the LNA's own input referred noise. 1.57 is the brickwall correction factor for single-pole role off.

With a total input referred noise of 8.4μVPP, the achieved SNR at 100μVPP at input is

Equation 4. S N R = 20 × log  ⁡ ×   100 µ V P P 8.4 µ V P P = 21.4 d B

To protect the LNA from high input voltage during burst / Tx mode or other unseen circumstances TI recommends to add a back to back diode at the input of the LNA to clamp the input voltage to 1.4VPP max.

The EN_VICM is enabled by connecting the pin to VCC_VGA since this is an AC coupled application. Enabling the EN_VICM allows the VGA sub-block to set the internal common mode voltage appropriately.

Applying an appropriate voltage between 0V to 1V on the GAIN_ADJ pin and toggling the HILO pin allows an overall gain of the VCA710 ( LNA + VGA ) from –12dB to +60dB,

Using the VOCM_ADJ pin an appropriate output common mode voltage can be set as per the ADC requirements. With ADC requiring 0V common-mode voltage, TI recommends using VCA710 in bi-polar/split supply mode to enable 0V common mode support.