+

±

+2.5V

9 NŸ

OPA607

2 NŸ

-2.5V

1.8 NŸ

300 Ÿ

SW

105 Ÿ

+

±

+2.5V

40 NŸ

OPA837

-2.5V

0.4 nF

0.4 nF

0.1

F

To ADC/FDA

Ultrasonic Sensor

100 NŸ

12

OPAX607

SBOS981B – OCTOBER 2019 – REVISED FEBRUARY 2020

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Product Folder Links: OPAX607

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Copyright © 2019–2020, Texas Instruments Incorporated

9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

9.1 Application Information

The OPAX607 features a 50-MHz gain bandwidth with 900 µA of supply current, providing good AC performance

at low-power consumption. The low input noise voltage of 3.8 nV/

√Hz, the approximate pA of bias current, and a

typical input offset voltage of 0.1 mV make the device very suitable for both AC and DC applications.

9.2 Typical Applications

9.2.1 High-Input Impedance (Hi-Z), Large-Gain Signal Front-End

Figure 4. Hi-Z, Large-Gain Front-End Circuit

9.2.1.1 Design Requirements

The objective is to design a high-input impedance, high-dynamic range, signal-conditioning front-end. An

example application for such a front-end circuit is the receive signal chain in an ultrasonic-based end equipment

(EE) such as fish finders, printers, and flow meters. Table 1 lists the design requirements for this application.

Table 1. Design Parameters

PARAMETER

DESIGN REQUIREMENT

Amplifier supply

±2.5 V

Input signal frequency

200 kHz

Minimum voltage

300 µVrms

Minimum SNR at 300 µVrms

40 dB

9.2.1.2 Detailed Design Procedure

The concept used in an ultrasonic transmit (Tx) and receive (Rx) system is to send a large-amplitude tone at a

known frequency and to calculate the time elapsed for the reflections to be received using a highly selective

band-pass filter and to calculate the distance using:

Distance = Time × Speed

(1)

Ultrasound speed is constant for a given medium and the time-of-flight (ToF) is calculated using the method

explained in this section. The transmitter creates these ultrasonic signals by exciting a piezo crystal at its

resonant frequency, which is in turn tuned to be in the ultrasonic frequency spectrum. Fish finders are one the

primary end equipments that use such a Tx and Rx system. Based on the aperture angle and the distance to be

measured in water, a frequency range from 50 kHz to 200 kHz is chosen as a base carrier frequency.