Frequency (Hz)

-30

-24

-18

-12

-6

0

6

12

18

1k

10k

100k

1M

10M

100M

Freq

Gain = 3 V/V with Noise Gain Shaping

Gain = 3 V/V without Noise Gain Shaping

Gain = 6 V/V

Figure 9-7. Small-Signal Frequency Response in

Gains of 3V/V (a) and 6V/V (b)

Frequency (Hz)

-30

-24

-18

-12

-6

0

6

12

18

24

30

1k

10k

100k

1M

10M

100M

OPA6

Without Noise Gain Shaping

With Noise Gain Shaping

Figure 9-8. Small-Signal Frequency Response of

Difference Amplifier (c) With and Without Noise

Gain Shaping

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

+

±

+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

Figure 9-9. Hi-Z, High-Gain Front-End Circuit

9.2.3.1 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 9-2 lists the design requirements for this application.

Table 9-2. 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

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OPA607, OPA2607

SBOS981F – OCTOBER 2019 – REVISED SEPTEMBER 2020

Copyright © 2020 Texas Instruments Incorporated

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