OPA328 datasheet(18/27 Pages) TI

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Figure 8-4 shows that the key elements to a transimpedance design are the:

• Expected diode capacitance (CD), which should include the parasitic input common-mode voltage and

differential-mode input capacitance

• Desired transimpedance gain (RF)

• Gain-bandwidth (GBW) = 40 MHz

With these three variables set, the feedback capacitor (CF) value can be set to control the frequency response.

CF includes the stray capacitance of RF, which is 0.2 pF for a typical surface-mount resistor.

–

V+

Amp

VOUT

10 M

V–

NOTE: CF is optional to prevent gain peaking, and includes the stray capacitance of RF.

Figure 8-4. Dual-Supply Transimpedance Amplifier

For optimal frequency response, use Equation 6 to set the feedback pole:

2 R C

4 R C

GBW

(6)

Equation 7 calculates the bandwidth:

3dB =

2 R C

GBW

(Hz)

(7)

For single-supply applications, the +IN input can be biased with a positive dc voltage to allow the output to reach

true zero when the photodiode is not exposed to any light, and respond without the added delay that results from

coming out of the negative rail. Figure 8-5 shows this configuration. This bias voltage also appears across the

photodiode, providing a reverse bias for faster operation.

–

V+

Amp

VOUT

10 M

VBIAS

NOTE: CF is optional to prevent gain peaking, and includes the stray capacitance of RF.

Figure 8-5. Single-Supply Transimpedance Amplifier

For additional information, see the Compensate Transimpedance Amplifiers Intuitively application report,

available for download at www.ti.com.

OPA2328

SBOS957A – FEBRUARY 2022 – REVISED JUNE 2022

www.ti.com

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