THS4601 Datasheet, PDF (15/27 Pages) Texas Instruments – WIDEBAND, FET-INPUT OPERATIONAL AMPLIFIER

THS4601
SLOS388B – OCTOBER 2001 – REVISED JUNE 2002
APPLICATION INFORMATION
designing the transimpedance circuit (continued)
Table 1. Transimpedance Performance Summary for Various Configurations
SOURCE CAPACITANCE
(pF)
18
18
18
47
47
47
100
100
100
220
220
220
TRANSIMPEDANCE GAIN
(Ω)
10k
100k
1M
10k
100k
1M
10k
100k
1M
10k
100k
1M
FEEDBACK CAPACITANCE
(pF)
2.2
0.6
0
3.3
0.6
0
3.9
1.5
0
5.6
1.8
0.4
–3 dB FREQUENCY
(MHz)
10.4
3.3
1.1
7.6
2.8
0.88
5.9
1.3
0.62
3.8
1.1
0.36
10 kΩ TRANSIMPEDANCE BANDWIDTH
FOR VARIOUS SOURCE CAPACITANCES
90
85
80
75
70
65
10 k
CS = 18 pF, CF = 2.2 pF
CS = 47 pF,
CF = 3.3 pF
CS = 100 pF,
CF = 3.9 pF
CS = 220 pF,
CF = 5.6 pF
100 k
1M
Frequency – Hz
10 M
Figure 29
100 M
100 kΩ TRANSIMPEDANCE BANDWIDTH
FOR VARIOUS SOURCE CAPACITANCES
105
100
95
90
85
80
75
70
65
60
10 k
CS = 18 pF,
CF = 0.6 pF
CS = 47 pF,
CF = 0.6 pF
CS = 100 pF,
CF = 1.5 pF
CS = 220 pF,
CF = 1.8 pF
100 k
1M
Frequency – Hz
10 M
Figure 30
1 MΩ TRANSIMPEDANCE BANDWIDTH
FOR VARIOUS SOURCE CAPACITANCES
130
125
CS = 18 pF, CF = 0
120
115
CS = 47 pF,
CF = 0
110
105
CS = 100 pF,
CF = 0
100
95
90
10 k
CS = 220 pF,
CF = 0.4 pF
100 k
1M
Frequency – Hz
10 M
Figure 31
measuring transimpedance bandwidth
While there is no substitute for measuring the performance of a particular circuit under the exact conditions that
are used in the application, the complete system environment often makes measurements harder. For
transimpedance circuits, it is difficult to measure the frequency response with traditional laboratory equipment
because the circuit requires a current as an input rather than a voltage. Also, the capacitance of the current
source has a direct effect on the frequency response. A simple interface circuit can be used to emulate a
capacitive current source with a network analyzer. With this circuit, transimpedance bandwidth measurements
are simplified, making amplifier evaluation easier and faster.
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