OPA607 datasheet(23/48 Pages) TI

23 / 48 page

9.2.1.2 Detailed Design Procedure

Designs that require high bandwidth from a large area detector with relatively high transimpedance-gain benefit

from the low input voltage noise of the OPAx607 devices. Use the Excel™ calculator available at What You Need

To Know About Transimpedance Amplifiers – Part 1 to help with the component selection based on total input

capacitance and CTOT. CTOT is referred as CIN in the calculator. CTOT is the sum of CD, CDIFF, and CCM which is

20 pF. Using this value of CTOT, and the targeted closed-loop bandwidth (f–3dB) of 2 MHz and transimpedance

gain of 100 kΩ results in amplifier GBW of approximately 50 MHz and a feedback capacitance (CF) of 1.1 pF

as shown in Figure 9-2. These results are for a Butterworth response with a Q = 0.707 and a phase margin of

approximately 65° which corresponds to 4.3% overshoot.

Closed-loop TIA Bandwidth (f-3dB)

2.00

MHz

Feedback Resistance (RF)

100.00

kOhm

Input Capacitance (CIN)

20.00

Opamp Gain Bandwidth Product (GBP)

50.27

MHz

Feedback Capacitance (CF)

1.110

Calculator II

Figure 9-2. Results of Inputting Design Parameters in the TIA Calculator

The OPA607's 50 MHz GBW, is suitable for the above design requirements. If the required feedback capacitance

CF comes out to be a very low value capacitor to be practically achievable, a T-Network capacitor circuit as

shown below can be used. A very low capacitor value (CEQ) can be achieved between Port1 and Port2 using

standard value capacitors in a T-Network circuit as shown in Figure 9-3.

(1)

GND

Port

Figure 9-3. T-Network

9.2.1.3 Application Curves

Frequency (Hz)

-400

-360

-320

-280

-240

-200

-160

-120

-80

-40

100

110

120

10k

100k

10M

100M

TIA_

Gain (dB)

Phase (q)

Figure 9-4. Simulated Closed-Loop Bandwidth of

TIA

Time (50 Psec/Div)

OPA6

VOUT

IPD

Figure 9-5. Simulated Time Domain Response

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OPA607, OPA2607

SBOS981J – OCTOBER 2019 – REVISED APRIL 2021

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