Datasheet

LT6230/LT6230-10
LT6231/LT6232
24
623012fc
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone]
●
FAX: [phone]
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www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2003
LT 0111 REV C • PRINTED IN USA
relaTeD parTs
Typical applicaTions
The LT6230 is applied as a transimpedance amplifier with
an I-to-V conversion gain of 1.5kΩ set by R1. The LT6230
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
LT6230 contributes only 1.1nV and 2.4pA /√Hz. So, with
respect to both voltage and current noises, the LT6230 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 measurement 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.
Low Power Avalanche Photodiode Transimpedance Amplifier
I
S
= 3.3mA
+
–
R1
1.5k
R2
1.5k
C2
0.1µF
5V
–5V
ENABLE
LT6230
≈200V BIAS
ADVANCED PHOTONIX
012-70-62-541
WWW.ADVANCEDPHOTONIX.COM
623012 TA02a
C1
4.7pF
OUTPUT OFFSET = 500µV TYPICAL
BANDWIDTH = 20MHz
OUTPUT NOISE = 1.1mV
P-P
(100MHz MEASUREMENT BW)
Photodiode Amplifier Time Domain Response
50ns/DIV
623012 TA02b
30mV/DIV
PART NUMBER DESCRIPTION COMMENTS
LT1028 Single, Ultralow Noise 50MHz Op Amp 0.85nV/√Hz
LT1677 Single, Low Noise Rail-to-Rail Amplifier 3V Operation, 2.5mA, 4.5nV/√Hz, 60µV Max V
OS
LT1806/LT1807 Single/Dual, Low Noise 325MHz Rail-to-Rail Amplifier 2.5V Operation, 550µV Max V
OS
, 3.5nV/√Hz
LT6200/LT6201 Single/Dual, Low Noise 165MHz 0.95nV√Hz, Rail-to-Rail Input and Output
LT6202/LT6203/LT6204 Single/Dual/Quad, Low Noise, Rail-to-Rail Amplifier 1.9nV/√Hz, 3mA Max, 100MHz Gain Bandwidth