Datasheet

LT6236/LT6237/LT6238
26
623637fa
For more information www.linear.com/LT6236
 LINEAR TECHNOLOGY CORPORATION 2012
LT 0913 REV A • PRINTED IN USA
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone]
●
FAX: [phone]
●
www.linear.com/LT6236
RELATED PARTS
TYPICAL APPLICATION
PART NUMBER DESCRIPTION COMMENTS
OPERATIONAL AMPLIFIERS
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LT6350 Low Noise, Single-Ended to Differential Converter/ADC Driver 4.8mA, –97dBc Distortion at 100kHz, 4V
P-P
Output
LTC6246/LTC6247/LTC6248 Single/Dual/Quad 180MHz Rail-to-Rail Low Power Op Amps 1mA/Amplifier, 4.2nV/√Hz
LTC6360 1GHz Very Low Noise Single-Ended SAR ADC Driver
with
True Zero Output
HD2 = –103dBc and HD3 = –109dBc for 4V
P-P
Output at 40kHz
ADCs
LTC2389-18 Low Power 18-Bit SAR ADC 2.5Msps
LTC2389-16 Low Power 16-Bit SAR ADC 2.5Msps
LTC2379-18
LTC2378-18
LTC2377-18
LTC2376-18
Low Power 18-Bit SAR ADC 1.6Msps
1Msps
500ksps
250ksps
+
–
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
OUTPUT NOISE = 1.1mV
P-P
(100MHz MEASUREMENT BW)
50ns/DIV
62367 TA07
30mV/DIV
Low Power Avalanche Photodiode Transimpedance Amplifier
I
S
= 3.3mA
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 5
nV/√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
I
PD
which flows into the amplifier circuit. The amplifier
output falls negative to maintain balance at its inputs.
The transfer function is therefore V
OUT
= –I
PD
• 1.5k. C1
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
noise was measured at 1.1mV
P–P
on a 100MHz measure-
ment bandwidth, with C2 shunting R
2’s thermal noise. As
shown in the scope photo, the rise time is 17ns, indicating
a signal bandwidth of 20MHz.