THS4601

SLOS388B – OCTOBER 2001 – REVISED JUNE 2002

18

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APPLICATION INFORMATION

alternative transimpedance configurations (continued)

The third configuration uses a capacitive T-network to achieve fine control of the compensation capacitance.

1

C

FEQ

+ 1

C

F1

1

)

C

F3

C

F2

_

+

CF2

RL

RF

–VBias

CF1

CF3

NOTE: A capacitive T-network enables fine control of the effective

feedback capacitance using relatively large capacitor values.

λ

Figure 35. Alternative Transimpedance Configuration #3

summary of key decisions in transimpedance design

The following is a quick, simplified process for basic transimpedance circuit design. This process gives a quick

start to the design process, though it does ignore some aspects that may be critical to the circuit.

Step 1:

Determine the capacitance of the source.

Step 2:

Step 3:

Determine the magnitude of the possible current output from the source, including the minimum

signal current anticipated and maximum signal current anticipated.

Step 4:

Choose a feedback resistor value such that the input current levels create the desired output signal

voltages, and ensure that the output voltages can accommodate the dynamic range of the input

signal.

Step 5:

Calculate the optimum feedback capacitance using equation 1.

Step 6:

Calculate the bandwidth given the resulting component values.

Step 7:

Evaluate the circuit to see if all design goals are satisfied.

(4)