LT6236/LT6237

24

623637f

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

© LINEAR TECHNOLOGY CORPORATION 2012

LT 1212 • PRINTED IN USA

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TYPICAL APPLICATION

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1 Msps

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+

–

R1

1.5k

R2

1.5k

C2

0.1μF

5V

–5V

ENABLE

LT6236

≈200V BIAS

ADVANCED PHOTONIX

012-70-62-541

WWW.ADVANCEDPHOTONIX.COM

62367 TA06

C1

4.7pF

OUTPUT OFFSET = 500μV TYPICAL

BANDWIDTH = 20MHz

50ns/DIV

62367 TA07

Low Power Avalanche Photodiode Transimpedance Amplifier

Photodiode Amplifier Time Domain Response

The LT6236 is configured as a transimpedance amplifier

with an I-to-V conversion gain of 1.5kΩ set by R1. The

LT6236 is ideally suited to this application because of its

low input offset voltage and current, and its low noise.

This is because the 1.5k resistor has an inherent thermal

noise of 5nV/√Hz or 3.4pA/√Hz at room temperature, while

the LT6236 contributes only 1.1nV/√Hz and 2.4pA/√Hz.

So, with respect to both voltage and current noises, the

LT6236 is actually quieter than the gain resistor. The

circuit uses an avalanche photodiode with the cathode

biased to approximately 200V. When light is incident on

the photodiode, it induces a current

output falls negative to maintain balance at its inputs.

ensures stability and good settling characteristics. Output

offset was measured at 280μV, so low in part because R2

serves to cancel the DC effects of bias current. Output

ment bandwidth, with C2 shunting R2’s thermal noise. As

shown in the scope photo, the rise time is 17ns, indicating

a signal bandwidth of 20MHz.