ADA4620-1ARZ-R7 datasheet(39/49 Pages) AD

39 / 49 page

Data Sheet

ADA4620-1, ADA4620-2

analog.com

Rev. 0

39 of 49

Figure 122 shows the total output noise for the photodiode preamp, where the preamp is configured for slight

overcompensation with a feedback capacitor CF = 1.5 pF. Total output noise is 520 µVRMS over a 2 MHz measurement

bandwidth.

Figure 122. Output Noise Spectrum

For more information, see the KWIK circuit application note: 1 MHz, Single Supply, Photodiode Transimpedance

Amplifier (TIA) Design.

ADC Driving

Figure 123. Squeezing a High Voltage High Impedance Signal into a 5 V Precision Differential Input ADC

The ADA4620 has high DC precision and very low bias current. Adding its low distortion, it is suitable for data

acquisition systems using high resolution ADCs. When an ADC samples its input, it puts a glitch onto the upstream

circuit, such that the upstream circuit must settle back out before the ADC closes its sample window, ending the

analog “acquisition” phase. Any unsettled residue from the glitch leads to increased noise and distortion in the

sample. Figure 123 shows an ADA4620-2 driving a 20 V p-p single-ended signal into a single-to-differential

converting circuit using the other half of the ADA4620-2 and an LT5400. The resulting differential voltages are fed

into the LTC2378-20, a 20-bit 1 MSps SAR ADC.

FREQUENCY (Hz)

20k

100k

100

200

300

400

500

600

700

800

–15V

+15V

1/2

ADA4620-2

VIN

+10V

–10V

+5V

1/2

ADA4620-2

20kΩ

10kΩ

10µF

VREF = 5V

10kΩ

LT5400-4

1kΩ

IN+

IN–

VREF

+5V

VDD

+2.5V

GND

LTC2378-20

SAR ADC

20-BIT

CD = 680pF, NP0

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