Data Sheet

ADA4352-2

analog.com

Rev 0

40 of 47

Figure 81.

Simulated PGTIA Frequency Response for Various Values of CD, RF2 = 40.2 kΩ

As the selected gain moves up to the next RF2 = 40.2 kΩ, CF2 = 7 pF setting, the response curves become even more

bandlimited, but F−3dB still increases as CD increases. Again, the output is changing from an overcompensated 2-real

pole response to a higher Q flat response, as CD increases from 5 pF to 25 pF, and then 45 pF. These response curves

are all clustered around 700 kHz F−3dB for this gain setting, as shown in Figure 81.

Figure 82.

Simulated PGTIA Frequency Response for Various Values of CD, RF3 = 450 kΩ

The highest RF3 = 450 kΩ, CF3 = 2.5 pF gain setting gives the most bandlimited response. Again, as the CD increases

from 5 pF to 25 pF and finally to 45 pF, the frequency response is moving from two real poles to a response with a

higher Q and extended bandwidth. These are all clustered around a 170 kHz F−3dB, as shown in Figure 82.

Increasing CD beyond 45 pF continues to make the frequency response poles more complex, with possibly

significant peaking. Carefully consider these effects if a higher CD is needed using the available simulation model.

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100k

FREQUENCY (Hz)

1M

10M

CD = 5pF

CD = 25pF

CD = 45pF

FREQUENCY (Hz)

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CD = 5pF

CD = 25pF

CD = 45pF

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100k

1M