TLC080 datasheet(13/33 Pages) TI2

13 / 33 page

OPA725, OPA2725

OPA726, OPA2726

SBOS278B − SEPTEMBER 2003 − REVISED JANUARY 2004

www.ti.com

To achieve a maximally-flat, 2nd-order Butterworth

frequency response, the feedback pole should be set to:

FCF

GBW

FCD

Bandwidth is calculated by:

f*3dB +

GBW

FCD

For

even

higher

transimpedance

bandwidth,

the

high-speed CMOS OPA354 (100MHz GBW), OPA300

(180 MHz GBW), OPA355 (200MHz GBW), or OPA656,

OPA657 (400MHz GBW) may be used.

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. (Refer to Figure 6.) This bias

voltage also appears across the photodiode, providing a

reverse bias for faster operation.

OPA725

OUT

10M

Ω

V+

(1)

<1pF

NOTE: (1) C

F is optional to prevent gain peaking.

It includes the stray capacitance of R

Bias

Figure 6. Single-Supply Transimpedance

Amplifier

For additional information, refer to Application Bulletin

SBOA055,

Compensate

Transimpedance

Amplifiers

Intuitively, available for download at www.ti.com.

OPTIMIZING THE TRANSIMPEDANCE

CIRCUIT

To achieve the best performance, components should be

selected according to the following guidelines:

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 is improved when all the required gain is placed

in the transimpedance stage.

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.

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.

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 the TI web site.

(1)

(2)

TLC080 数据表(PDF) 13 Page - Texas Instruments

TLC080 数据表(HTML) 13 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33

数据表下载