OPA320SAIDBVT datasheet(23/58 Pages) TI2

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OPA320

OUT

V+

10MW

< 1pF

(1)

BIAS

OPA320, OPA2320, OPA320S, OPA2320S

www.ti.com

SBOS513F – AUGUST 2010 – REVISED DECEMBER 2016

Product Folder Links: OPA320 OPA2320 OPA320S OPA2320S

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Application Information (continued)

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; this configuration is shown in Figure 41. This bias voltage also appears across

the photodiode, providing a reverse bias for faster operation.

(1)

CF is optional to prevent gain peaking. It includes the stray capacitance of RF.

Figure 41. Single-Supply Transimpedance Amplifier

For additional information, see the Application Bulletin Compensate Transimpedance Amplifiers Intuitively

(SBOA055), available for download at www.ti.com.

8.1.2 Optimizing the Transimpedance Circuit

To achieve the best performance, components should be selected according to the following guidelines:

1. For lowest noise, select RF to create the total required gain. Using a lower value for RF and adding gain after

the transimpedance amplifier generally produces poorer noise performance. The noise produced by RF

increases with the square-root of RF, whereas the signal increases linearly. Therefore, signal-to-noise ratio

improves when all the required gain is placed in the transimpedance stage.

2. Minimize photodiode capacitance and stray capacitance at the summing junction (inverting input). This

capacitance causes the voltage noise of the op amp to be amplified (increasing amplification at high

frequency). Using a low-noise voltage source to reverse-bias a photodiode can significantly reduce its

capacitance. Smaller photodiodes have lower capacitance. Use optics to concentrate light on a small

photodiode.

3. Noise increases with increased bandwidth. Limit the circuit bandwidth to only that required. Use a capacitor

across the RF to limit bandwidth, even if not required for stability.

4. Circuit board leakage can degrade the performance of an otherwise well-designed amplifier. Clean the circuit

board carefully. A circuit board guard trace that encircles the summing junction and is driven at the same

voltage can help control leakage.

For additional information, refer to the Application Bulletins Noise Analysis of FET Transimpedance Amplifiers

(SBOA060), and Noise Analysis for High-Speed Op Amps (SBOA066), available for download at www.ti.com.

OPA320SAIDBVT Datasheet(PDF) 23 Page - Texas Instruments