OPAX607 datasheet(26/52 Pages) TI

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9.2.2 Front-End Gain and Filtering

RBIAS

-VBIAS

RISO

VS+

VS-

CSH

High-Gain Band Pass Filt er

High-Speed Peak Detector

Figure 9-3. High-Gain Narrow Bandpass Filter and Peak Detector Circuit

Ultrasonic signaling is used for proximity and obstacle detection, level sensing, sonars, and so forth. Such signal

chains detect the amplitude of received ultrasonic signal at a particular center frequency. Figure 9-3 shows a

high-gain narrow bandpass filter and peak detector circuit using any of the OPAx863 devices. The signal at the

frequency of interest is filtered out, gained, and peak detected to report the amplitude at the output of this circuit.

The phase information is lost in this circuit. The OPAx863 devices are used with the 50-MHz GBW to add a

single-stage gain and filtering, and the peak detection capability is easily made with the RRIO capability of these

amplifiers.

9.2.3 Low-Power SAR ADC Driver and Reference Buffer

Figure 9-4 shows the use of the OPAx863 as a SAR ADC input driver and reference buffer driving the ADS7945.

sensors, which are used for interface with the physical environment, exhibit high output impedance, and cannot

drive SAR ADC inputs directly. A wide-GBW amplifier, such as the OPAx863, is needed to charge the switching

capacitors at the SAR ADC input, and quickly settle to the required accuracy within the given acquisition time.

The ADC core draws transient current from the reference input during the conversion (digitization) phase, which

must be driven with a wide-GBW amplifier to offer fast settling and maintain a stable reference voltage for

excellent digitization performance. The OPAx863 reference buffer is used in a composite loop with the OPA378

precision amplifier because of limitations in precision performance of wide-GBW amplifiers. The precision

amplifier maintains low-offset output, whereas the OPAx863 devices provide the output drive and fast-settling

performance.

ADS7945

14-bit

2 MSPS

–

6 V

AVDD

DVDD

5 V

OPAx863

–

6 V

OPAx863

VREF

FILT

–

5 V

OPA378

REF5050

5.0 V

Reference

12 V

OUT

Sensor

Figure 9-4. OPAx863 as Low-Power SAR ADC Driver

OPA863, OPA2863, OPA4863

SBOS982J – JUNE 2020 – REVISED JUNE 2023

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