OPA863 datasheet(15/24 Pages) TI

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Frequency (Hz)

-10

100

10k

100k

10M

100M

D801

AOL

1/E

AOLE

Frequency (Hz)

100

10k

100k

10M

100M

D802

AOL

1/E

AOLE

%( =

è:0.707;4(BF3@$

OPA2863

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SBOS982A – JUNE 2020 – REVISED JUNE 2020

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The small input capacitance of OPAx863 helps to achieve a wider small-signal bandwidth, mainly limited by the

photodiode capacitance. The feedback resistor RF introduces a zero in the noise gain with the total input

capacitance CIN and a 40 dB/dec rate of closure. Figure 12 shows the feedback capacitor CF that is needed to

cancel the zero due to RF, CIN with a pole in the noise gain, whose value is given below for a 65° phase margin

and butterworth response.

estimates a closed-loop bandwidth of 2.6 MHz. Figure 13 and Figure 14 show the closed-loop gain and phase

plots from TINA-TI simulation of the TIA circuit of Figure 12. The 1/β gain curve has a zero from RF and CIN at

142 kHz and a pole from RF and CF cancelling the 1/β zero at 1.87 MHz, resulting in a 20-dB per decade rate-of-

closure at the loop-gain crossover frequency (the frequency where AOL equals 1/β), ensuring a stable circuit. A

phase margin of 65° is obtained with a closed-loop bandwidth of 2.6 MHz and a 100-kΩ transimpedance gain.

9.3.3 Application Curves

Figure 13. Loop-Gain Magnitude vs Frequency for the

Transimpedance Amplifier Circuit of Figure 12

Figure 14. Loop-Gain Phase vs Frequency for the

Transimpedance Amplifier Circuit of Figure 12

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