Texas Instruments THS4631DGNEVM Evaluation Module THS4631DGNEVM THS4631DGNEVM データシート
製品コード
THS4631DGNEVM
65
70
75
80
85
10 k
100 k
1 M
10 M
1 G
f − Frequency − Hz
T
ransimpedance Gain − dB
V
S
=
±
15 V
R
L
= 1 k
R
F
= 10 k
C
S
= 100 PF
C
F
= 3 PF
C
S
= 18 PF
C
F
= 2 PF
C
S
= 47 PF
C
F
= 2.2 PF
50
W
50
W
R
S
V
S
C1
C2
I
O
Network Analizer
I
O
V
S
(s)
+
1
2 R
S
ǒ
1
)
C1
C2
C2
Ǔ
(Above the Pole Frequency)
I
O
V
S
(s)
+
s
2 R
S
ǒ
1
)
C1
C2
C2
Ǔ
s
)
1
2 R
S
ǒ
C1
)
C2
Ǔ
85
90
95
100
105
10 k
100 k
1 M
10 M
1 G
f − Frequency − Hz
T
ransimpedance Gain − dB
V
S
=
±
15 V
R
L
= 1 k
R
F
= 100 k
C
S
= 47 PF
C
F
= 0.7 PF
C
S
= 100 PF
C
F
= 1 PF
C
S
= 18 PF
C
F
= 0.5 PF
1
2 R
S
(
C1
)
C2
)
1
2 R
S
ǒ
1
)
C1
C2
C2
Ǔ
95
100
110
120
10 k
100 k
1 M
10 M
f − Frequency − Hz
T
ransimpedance Gain − dB
125
V
S
=
±
15 V
R
L
= 1 k
R
F
= 1 M
115
105
C
S
= 18 PF
C
F
= 0 PF
C
S
= 47 PF
C
F
= 0.2 PF
C
S
= 100 PF
C
F
= 0.2 PF
Z
O
(s)
+
C1
)
C2
C1
C2
ȧ
ȱ
Ȳ
s
)
1
2 R
S
ǒ
C1
)
C2
Ǔ
s
ǒ
s
)
1
2 R
S
C1
Ǔ
ȧ
ȳ
ȴ
Z
O
[
1
s C2
SLOS451B
–
DECEMBER 2004
–
REVISED AUGUST 2011
Table 1. Transimpedance Performance Summary
is difficult to measure the frequency response with
for Various Configurations (continued)
traditional laboratory equipment because the circuit
requires a current as an input rather than a voltage.
requires a current as an input rather than a voltage.
10-k
Ω
TRANSIMPEDANCE RESPONSES
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, trans- impedance bandwidth measurements
are simplified, making amplifier evaluation easier and
faster.
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, trans- impedance bandwidth measurements
are simplified, making amplifier evaluation easier and
faster.
Figure 35.
A.
The interface network creates a capacitive,
100-k
Ω
TRANSIMPEDANCE RESPONSES
constant current source from a network
analyzer
analyzer
and
properly
terminates
the
network analyzer at high frequencies.
Figure 38. Emulating a Capacitive Current Source
With a Network Analyzer
The
transconductance
transfer
function
of
the
interface circuit is:
(3)
The transfer function contains a zero at dc and a pole
Figure 36.
1-M
Ω
TRANSIMPEDANCE RESPONSES
at:
. The transconductance is constant
at:
,
above
the
pole
frequency,
providing a controllable ac-current source. This circuit
also properly terminates the network analyzer with 50
also properly terminates the network analyzer with 50
Ω
at high frequencies. The second requirement for
this current source is to provide the desired output
impedance, emulating the output impedance of a
photodiode or other current source. The output
impedance of this circuit is given by:
impedance, emulating the output impedance of a
photodiode or other current source. The output
impedance of this circuit is given by:
Figure 37.
(4)
Assuming C1
>>
C2, the equation reduces to:
MEASURING TRANSIMPEDANCE
BANDWIDTH
BANDWIDTH
, giving the appearance of a capacitive
While there is no substitute for measuring the
source at a higher frequency.
performance of a particular circuit under the exact
conditions that are used in the application, the
conditions that are used in the application, the
Capacitor values should be chosen to satisfy two
complete
system
environment
often
makes
requirements. First, C2 represents the anticipated
measurements harder. For transimpedance circuits, it
capacitance of the true source. Second C1 is chosen
Copyright
©
2004
–
2011, Texas Instruments Incorporated
11