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OPA2320-Q1_15 Datasheet, PDF (17/31 Pages) Texas Instruments – Precision, 20-MHz, 0.9-pA, Low-Noise, RRIO,CMOS Operational Amplifier
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8 Application And Implementation
OPA2320-Q1
SLOS884 – SEPTEMBER 2014
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
8.1 Application Information
The OPA2320-Q1 device can be used in a wide range of applications such as a transimpedance amplifier, high-
impedance sensor, active filter, and for driving ADCs.
8.2 Typical Applications
8.2.1 Transimpedance Amplifier
Wide gain bandwidth, low input bias current, low input voltage, and current noise make the OPA2320-Q1 device
an ideal wideband photodiode transimpedance amplifier. Low-voltage noise is important because photodiode
capacitance causes the effective noise gain of the circuit to increase at high frequency.
The key elements to a transimpedance design, as shown in Figure 36, are the expected diode capacitance
(C(D)), which should include the parasitic input common-mode and differential-mode input capacitance (4 pF + 5
pF); the desired transimpedance gain (R(FB)); and the gain-bandwidth (GBW) for the OPA2320-Q1 device (20
MHz). With these three variables set, the feedback capacitor value (C(FB)) can be set to control the frequency
response. C(FB) includes the stray capacitance of R(FB), which is 0.2 pF for a typical surface-mount resistor.
C(F)(1)
< 1 pF
R(F)
10 MΩ
V(V+)
l
C(D)
OPA320-Q1
VO
V(V–)
(1) C(FB) is optional to prevent gain peaking. C(FB) includes the stray capacitance of R(FB).
Figure 36. Dual-Supply Transimpedance Amplifier
8.2.1.1 Design Requirements
PARAMETER
Supply voltage V(V+)
Supply voltage V(V-)
VALUE
2.5 V
–2.5 V
8.2.1.2 Detailed Design Procedure
To achieve a maximally-flat, second-order Butterworth frequency response, the feedback pole should be set to:
1
GBW
=
2 ´ p ´ R(FB) ´ C(FB) 4 ´ p ´ R(FB) ´ C(D)
(2)
Use Equation 3 to calculate the bandwidth.
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