OPA380 Datasheet, PDF (13/18 Pages) Burr-Brown (TI) – Precision, High-Speed Transimpedance Amplifier

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OPA380
OPA2380
SBOS291E − NOVEMBER 2003 − REVISED NOVEMBER 2004
110
C_DIODE = 10pF
80
50
See Figure 6a
−3dB BW at 1MHz
See Figure 6c
20
See Figure 6b
−10
100
1k
10k 100k
1M
10M 100M
Frequency (Hz)
500
C_DIODE = 10pF
400
300
See Figure 6a
419µV
200
100
0
1
See Figure 6b
See Figure 6c
86µV
30µV
10 100 1k 10k 100k 1M 10M 100M
Frequency (Hz)
Figure 7. Transimpedance gains for circuits in
Figure 6
The effect of these circuit configurations on output noise
is shown in Figure 8 and on integrated output noise in
Figure 9. A 2-pole Butterworth filter (maximally flat in
passband) is created by selecting the filter values using
the equation:
C_FR_F + 2C_FILTERR_FILTER
(4)
with:
Ǹ ^{f*3dB +}
1
2p R_FR_FILTERC_FC_FILTER
(5)
The circuit in Figure 6b rolls off at 20dB/decade. The
circuit with the additional filter shown in Figure 6c rolls
off at 40dB/decade, resulting in improved noise
performance.
300
C_DIODE = 10pF
200
See Figure 6a
100
See Figure 6b
See Figure 6c
0
1 10 100 1k 10k 100k 1M 10M 100M
Frequency (Hz)
Figure 9. Integrated output noise for circuits in
Figure 6
Figure 10 shows the effect of diode capacitance on
integrated output noise, using the circuit in Figure 6c.
For additional information, refer to Noise Analysis of
FET Transimpedance Amplifiers (SBOA060), and
Noise Analysis for High Speed Op Amps (SBOA066),
available for download from the TI web site.
79µV
80
C_DIODE
= 100pF
60
C_DIODE
= 50pF _50µV
0
20
See Figure 6c
0
1 10 100
C_DIODE
= 20pF
35µV
30µV
27µV
C_DIODE
= 10pF
C_DIODE
= 1pF
1k 10k 100k 1M 10M 100M
Frequency (Hz)
Figure 10. Integrated output noise for various
values of C_DIODE for circuit in Figure 6c
Figure 8. Output noise for circuits in Figure 6
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