OPA354-Q1_15 Datasheet, PDF (17/36 Pages) Texas Instruments – OPAx354-Q1 250-MHz, Rail-to-Rail I/O, CMOS Operational Amplifiers

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OPA354-Q1, OPA2354-Q1, OPA4354-Q1
SBOS492B – JUNE 2009 – REVISED DECEMBER 2014
Feature Description (continued)
The key elements to a transimpedance design, as shown in Figure 36, are the expected diode capacitance
(including the parasitic input common-mode and differential-mode input capacitance (2 + 2) pF for the OPAx354-
Q1), the desired transimpedance gain (R_F), and the gain-bandwidth product (GBW) for the OPAx354-Q1 family of
devices (100 MHz). With these three variables set, the feedback capacitor value (C_F) can be set to control the
frequency response.
C_F
< 1pF
(prevents gain peaking)
R_F
10MW
+V
l
C_D OPA354-Q1
V_OUT
Figure 36. Transimpedance Amplifier
To achieve a maximally flat second-order Butterworth frequency response, set the feedback pole as shown in
Equation 1.
Ǹ ¹
2pR_FC_F
+
GBP
4pR_FC_D
(1)
Typical surface-mount resistors have a parasitic capacitance of approximately 0.2 pF that required deduction
from the calculated feedback capacitance value.
Use Equation 2 to calculate the bandwidth.
Ǹ f_*3dB +
GBP _Hz
2pR_FC_D
(2)
For even higher transimpedance bandwidth, use the high-speed CMOS OPA355-Q1 (200-MHz GBW) or the
OPA655-Q1 (400-MHz GBW).
7.4 Device Functional Modes
The OPAx354-Q1 family of devices is powered on when the supply is connected. The devices can be operated
as single supply operational amplifiers or dual supply amplifiers depending on the application. The devices can
also be used with asymmetrical supplies as long as the differential voltage (V– to V+) is at least 1.8 V and no
greater than 5.5 V (example: V– set to –3.5 V and V+ set to 1.5 V).
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