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IVC102P Schematic ( PDF Datasheet ) - Burr-Brown Corporation

Teilenummer IVC102P
Beschreibung PRECISION SWITCHED INTEGRATOR TRANSIMPEDANCE AMPLIFIER
Hersteller Burr-Brown Corporation
Logo Burr-Brown Corporation Logo 




Gesamt 10 Seiten
IVC102P Datasheet, Funktion
® IVC102
PRECISION SWITCHED INTEGRATOR
TRANSIMPEDANCE AMPLIFIER
APPLICATIONS
q PRECISION LOW CURRENT MEASUREMENT
q PHOTODIODE MEASUREMENTS
q IONIZATION CHAMBER MEASUREMENTS
q CURRENT/CHARGE-OUTPUT SENSORS
q LEAKAGE CURRENT MEASUREMENT
FEATURES
q ON-CHIP INTEGRATING CAPACITORS
q GAIN PROGRAMMED BY TIMING
q LOW INPUT BIAS CURRENT: 750fA max
q LOW NOISE
q LOW SWITCH CHARGE INJECTION
q FAST PULSE INTEGRATION
q LOW NONLINEARITY: 0.005% typ
q 14-PIN DIP, SO-14 SURFACE MOUNT
DESCRIPTION
The IVC102 is a precision integrating amplifier with
FET op amp, integrating capacitors, and low leakage
FET switches. It integrates low-level input current for
a user-determined period, storing the resulting voltage
on the integrating capacitor. The output voltage can be
held for accurate measurement. The IVC102 provides
a precision, lower noise alternative to conventional
transimpedance op amp circuits that require a very
high value feedback resistor.
The IVC102 is ideal for amplifying low-level sensor
currents from photodiodes and ionization chambers.
The input signal current can be positive or negative.
TTL/CMOS-compatible timing inputs control the inte-
gration period, hold and reset functions to set the
effective transimpedance gain and to reset (discharge)
the integrator capacitor.
Package options include 14-Pin plastic DIP and SO-14
surface-mount packages. Both are specified for the
–40°C to 85°C industrial temperature range.
Ionization
Chamber
6 C3 60pF
VB
5 C2 30pF
4 C1 10pF
3
IIN 2
1
S1
S2
Photodiode
Analog
Ground
11 12
S1 S2
Logic Low closes switches
V+
14
10
VO
9
13 V–
Digital
Ground
V
O=
–1
CINT
IIN(t) dt
Positive or Negative
Signal Integration
0V
Hold Integrate Hold
S1
S2
Reset
InternationalAirportIndustrialPark • MailingAddress:POBox11400 • Tucson,AZ85734 • StreetAddress:6730S.TucsonBlvd. • Tucson,AZ 85706
Tel:(520)746-1111 • Twx:910-952-1111 • Cable:BBRCORP • Telex:066-6491 • FAX:(520)889-1510 • ImmediateProductInfo:(800)548-6132
© 1996 Burr-Brown Corporation
PDS-11329A
IVC102Printed in U.S.A. June, 1996
®






IVC102P Datasheet, Funktion
In addition, the offset voltage of the internal op amp and
charge injection of S2 contribute to the voltage on CINT at the
start of integration.
Performance of this basic approach can be improved by
sampling VO after the reset period at T1 and subtracting this
measurement from the final sample at T2. Op amp offset
voltage, charge injection effects and I•RS2 offset voltage on
S2 are removed with this two-point measurement. The effec-
tive integration period is the time between the two measure-
ments, T2-T1.
COMPARISON TO CONVENTIONAL TRANSIMPEDANCE AMPLIFIERS
With the conventional transimpedance amplifier circuit
of Figure 2a, input current flows through the feedback
resistor, RF, to create a proportional output voltage.
VO = –IIN RF
The transimpedance gain is determined by RF. Very large
values of RF are required to measure very small signal
current. Feedback resistor values exceeding 100Mare
common.
The IVC102 (Figure 2b) provides a similar function,
converting an input current to an output voltage. The
input current flows through the feedback capacitor, CINT,
charging it at a rate that is proportional to the input
current. With a constant input current, the IVC102’s
output voltage is
VO = –IIN TINT/ CINT
after an integration time of TINT.
Conventional Transimpedance Amplifier
Figure 2a
VO is proportional to the integration time, TINT, and
inversely proportional to the feedback capacitor, CINT.
The effective transimpedance gain is TINT /CINT. Ex-
tremely high gain that would be impractical to achieve
with a conventional transimpedance amplifier can be
achieved with small integration capacitor values and/or
long integration times. For example the IVC102 with
CINT = 100pF and TINT = 100ms provides an effective
transimpedance of 1G. A 10nA input current would
produce a 10V output after 100ms integration.
The integrating behavior of the IVC102 reduces noise by
averaging the input noise of the sensor, amplifier, and
external sources.
Integrating Transimpedance Amplifier
Figure 2b
IIN RF
IIN CINT
VO
VO = –IIN RF
Provides time-continuous output
voltage proportional to IIN.
VO
V
O=
–1
CINT
IIN(t) dt
for constant IIN, at the end of TINT
VO = –IIN
TINT
CINT
Output voltage after integration period is
proportional to average IIN throughout
the period.
FIGURE 2. Comparison to a Conventional Transimpedance Amplifier.
CURRENT-OUTPUT SENSORS
Figure 3 shows a model for many current-output sensors
such as photodiodes and ionization chambers. Sensor output
is a signal-dependent current with a very high source resis-
tance. The output is generally loaded into a low impedance
so that the terminal voltage is kept very low. Typical sensor
capacitance values range from 10pF to over 100pF. This
capacitance plays a key role in operation of the switched-
input measurement technique (see next section).
®
IVC102
6

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