Transimpedance Amplifier
3-7
EVM Applications
Figure 3-7. Transimpedance Circuit Bode Plot
20 dB/Decade
Rate-of-Closure
GBP
20 dB/
Decade
-20 dB/
Decade
A
OL
Noise Gain
0
Gain
Zero
Pole
f
The performance of the THS4601 has been measured for a variety of
transimpedance gains with a variety of source capacitances. The achievable
bandwidths of the various circuit configurations are summarized numerically
in the data sheet, SLOS388.
Note that the feedback capacitances do not correspond exactly with the values
predicted by the equation. They have been tuned to account for the parasitic
capacitance of the feedback resistor (typically 0.2 pF for 0805 surface mount
devices) as well as the additional capacitance associated with the PC board.
The equation should be used as a starting point for the design, with final values
for Z5 optimized in the laboratory. Figure 3-8 shows 10 k
Ω
, 100 k
Ω
, and 1 M
Ω
transimpedance gains for various values of feedback capacitors.