廬
APPLICATION BULLETIN
Mailing Address: PO Box 11400 鈥?Tucson, AZ 85734 鈥?Street Address: 6730 S. Tucson Blvd. 鈥?Tucson, AZ 85706
Tel: (602) 746-1111 鈥?Twx: 910-952-111 鈥?Telex: 066-6491 鈥?FAX (602) 889-1510 鈥?Immediate Product Info: (800) 548-6132
COMPARISON OF NOISE PERFORMANCE BETWEEN A
FET TRANSIMPEDANCE AMPLIFIER AND A
SWITCHED INTEGRATOR
By Bonnie C. Baker
Low-input current FET operational amplifiers are univer-
sally used to monitor photodetector, or more commonly
photodiode currents. These photodetectors bridge the gap
between a physical event, light, and electronics. There are a
variety of amplifier configurations to select from and the
choice is based on noise, bandwidth, offset, and linearity.
The most popular design approach is shown in Figure 1. A
considerable amount has been written on the performance of
this traditional transimpedance amplifier. This topology has
dominated applications such as CT scanners, star-tracking
instruments, electron microscopes, etc., where a light-to-
voltage conversion is required.
To prevent gain peaking
C
2
(a)
R
EQ
R
3
I
IN
HP5082-4204
10M鈩?/div>
R
5
200pF
R
4
10M鈩?/div>
100k鈩?/div>
OPA128
e
O
R
EQ
= R
3
+ R
4
+ (R
3
R
4
/R
5
)
= 1000M鈩?/div>
R
2
1000M鈩?/div>
0.01碌F
R
2
+15V
Guard
A
1
I
IN1
(b)
A
1
A
2
: 1/2 OPA2111
INA105
R
2
R
25k鈩?/div>
R
25k鈩?/div>
I
IN
OPA124
Output
C
IN(1)
R
IN(1)
鈥?5V
I
IN
50M鈩?/div>
D
1
A
3
e
O
Circuit must be well shielded.
NOTE: (1) R
IN
and C
IN
used to reduce DC and AC errors caused by input
bias currents, however, R
IN
also increases noise at the output by a factor
of
鈭?KTRB
times the noise gain of the circuit.
R
2
50M鈩?/div>
I
IN2
A
2
R
25k鈩?/div>
R
25k鈩?/div>
FIGURE 1. Most Popular Design Approach to Gain Precise
Low Level Currents from a Photodetector.
Until now, the only feasible solution to the high precision,
current-to-voltage design problem has been an op amp
network with a resistor in the feedback loop. Variations such
as using resistor T-networks or an instrumentation amplifier,
as shown in Figure 2, still use the fundamental concept of a
resistive feedback loop to perform the I/V conversion func-
tion. In these circuits, the fundamental transfer function is:
e
O
= (I
IN1
鈥?I
IN2
)R
2
R
EQ
= R
2
e
O
= 2 I
IN
R
2
R
EQ
= 2R
2
FIGURE 2 (a) Using a T-Network to Design the Feedback
Resistor for a Transimpedance Circuit.
(b) An Instrumentation Amplifier Topology Can
Be Used to Convert Low-Level Photodiode Cur-
rents to a Voltage Output.
漏
1993 Burr-Brown Corporation
AB-057A
Printed in U.S.A. January, 1994
AB-057相關(guān)型號(hào)PDF文件下載
-
型號(hào)
版本
描述
廠商
下載
-
英文版
AB-001 - INCREASING INA117 DIFFERENTIAL INPUT RANGE
ETC
-
英文版
AB-002 - MAKE A PRECISION CURRENT SOURCE OR CURRENT SINK
ETC
-
英文版
AB-003 - VOLTAGE-REFERENCE FILTERS
ETC
-
英文版
AB-004 - MAKE A PRECISION -10V REFERENCE
ETC
-
英文版
AB-005 - Make A Precision -10V Reference
ETC
-
英文版
AB-006 - Make a -10V to +10V Adjustable Precision Voltage So...
ETC
-
英文版
AB-007 - CLASSICAL OP AMP OR CURRENT-FEEDBACK OP AMP?
ETC
-
英文版
AB-008 - AC COUPLING INSTRUMENTATION AND DIFFERENCE AMPLIFIE...
ETC
-
英文版
AB-009 - SINGLE-SUPPLY OPERATION OF ISOLATION AMPLIFIERS
ETC
-
英文版
AB-010 - -200V DIFFERENCE AMPLIFIER WITH COMMON-MODE VOLTAGE...
ETC
-
英文版
AB-011 - LOW POWER SUPPLY VOLTAGE OPERATION OF REF102 10.0V ...
ETC
-
英文版
AB-012 - BOOST ISO120 BANDWIDTH TO MORE THAN 100kHz
ETC
-
英文版
AB-013 - INCREASING ADC603 INPUT RANGE
ETC
-
英文版
AB-014 - INPUT OVERLOAD PROTECTION FOR THE RCV420 4-20mA CUR...
ETC
-
英文版
AB-015 - EXTENDING THE COMMON-MODE RANGE OF DIFFERENCE AMPLI...
ETC
-
英文版
AB-016 - BOOST AMPLIFIER OUTPUT SWING WITH SIMPLE MODIFICATI...
ETC
-
英文版
AB-017 - Sallen-Key Low-Pass Filter Design Program
ETC
-
英文版
AB-018 - 0 TO 20mA RECEIVER USING RCV420
ETC
-
英文版
AB-019 - USING THE ADS7800 12 BIT ADC WITH UNIPOLAR INPUT SI...
ETC
-
英文版
AB-020 - BURR-BROWN SPICE BASED MACROMODELS. REV. F
ETC
1
2
3
4
5
6
7
