ADC3683 datasheet(44/70 Pages) TI1

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8 Application Information Disclaimer

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, as well as validating and testing their design

implementation to confirm system functionality.

8.1 Application Information

A spectrum analyzer is a typical frequency domain application for the ADC3683-SP. The front end circuitry is

similar to several other systems such as software defined radio (SDR), sonar, radar or communications. Some

applications require frequency coverage including DC or near DC, such as sonar, which is included in this

example.

8.2 Typical Application

Control

AIN

CLK

VREF

ADC

0.95V

VCM

DB0/1

DCLKIN

DCLK

FCLK

DA0/1

Dig I/F

FPGA

1.2V REF

REFBUF

10 k

0.6V

Device Clock

AMP

CVCM

NCO

Low Pass Filter

180nH

100 pF

Glitch Filter

AMP

Low Pass Filter

180nH

100 pF

Glitch Filter

BIN

10 uF

Figure 8-1. Typical Configuration for a Spectrum Analyzer with DC Support

8.2.1 Design Requirements

Frequency domain applications cover a wide range of frequencies from low input frequencies at or near DC in

the 1st Nyquist zone to undersampling in higher Nyquist zones. If low input frequency is supported, then the

input has to be DC coupled and the ADC driven by a fully differential amplifier (FDA). If low frequency support is

not needed, then AC coupling and use of a balun may be more suitable.

The internal reference is used since DC precision is not needed. However, the ADC AC performance is highly

dependent on the quality of the external clock source. If in-band interferes can be present, then the ADC

SFDR performance is a key care about as well. A higher ADC sampling rate is desirable to relax the external

anti-aliasing filter, an internal decimation filter can be used to reduce the digital output rate afterward.

ADC3683-SP

SBASAB5 – MARCH 2024

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