THS4601

SLOS388B – OCTOBER 2001 – REVISED JUNE 2002

17

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APPLICATION INFORMATION

alternative transimpedance configurations

Other transimpedance configurations are possible. Three possibilities are shown below.

The first configuration is a slight modification of the basic transimpedance circuit. By splitting the feedback

resistor, the feedback capacitor value becomes more manageable and easier to control. This type of

compensation scheme is useful when the feedback capacitor required in the basic configuration becomes so

small that the parasitic effects of the board and components begin to dominate the total feedback capacitance.

By reducing the resistance across the capacitor, the capacitor value can be increased. This mitigates the

dominance of the parasitic effects.

_

+

CF

RF2

RL

RF1

–VBias

λ

NOTE: Splitting the feedback resistor enables use of a larger, more manageable feedback

capacitor.

Figure 33. Alternative Transimpedance Configuration #1

The second configuration uses a resistive T-network to achieve very high transimpedance gains using relatively

small resistor values. This topology can be very useful when the desired transimpedance gain exceeds the

value of available resistors. The transimpedance gain is given by equation 3.

R

R

R

F2

R

F3

_

+

CF

RF2

RL

RF1

–VBias

RF3

λ

NOTE: A resistive T-network enables high transimpedance gain with reasonable resistor values.

Figure 34. Alternative Transimpedance Configuration #2

(3)