Datasheet

-26
-24
-22
-20
-18
-16
-14
-12
-10
-8
-6
-4
-2
0
0.1 1 10 100
1000
f-Frequency(MHz)
Gain(dB)
V
S+
= 3 Vto 5 V
CM
V
SIGNAL
V
S-
R
F
R
F
R
G
R
G
R
T
R
O
R
O
V
OUT+
V
OUT-
THS4513
C
R
S
R
T
C
C
R
S
C
2.5V
348 W
348 W
340 W
340 W
56.2 W
V
IN
25 W
25 W
56.2 W50 W
THS4513
0.22 Fm
To50 Test
Equipment
-W
0.1 Fm
0.1 Fm
-2.5V
CM
1:1
6.8pF
6.8pF
V
OUT
0.22 Fm
0.22 Fm
50-W
Single-
Ended
AC-Coupled
Source
THS4513
www.ti.com SLOS472E –AUGUST 2005–REVISED JANUARY 2013
V
IC
is the desired input common-mode voltage, V
CM
= driving 50-Ω test equipment. The circuit as shown
CM, and R
IN
= R
G
+ R
S
|| R
T
. To set to midsupply, has an overall gain of –6 dB due to the voltage
make the value of R
PU
= R
G
+ R
S
|| R
T
. divider on the device output, and has a roll-off
frequency of approximately 60 MHz. The measured
Table 3 is a modification of Table 1 to add the proper
gain versus frequency response of the overall circuit
values with R
PU
assuming a 50-Ω source impedance
is shown in Figure 83. The low-frequency roll-off is
and setting the input and output common-mode
due to losses in the output transformer at those
voltage to midsupply.
frequencies.
There are two drawbacks to this configuration. One is
that it requires additional current from the power
supply. Using the values shown for a gain of 0 dB
requires 14 mA more current with 5-V supply, and 8.2
mA more current with 3-V supply.
The other drawback is that this configuration also
increases the noise gain of the circuit. In the 10-dB
gain case, noise gain increases by a factor of 1.5.
Table 3. R
PU
Values for Various Gains
Gain R
F
R
G
R
IT
R
PU
0 dB 348 Ω 340 Ω 56.2 Ω 365 Ω
6 dB 348 Ω 168 Ω 64.9 Ω 200 Ω
Figure 81 shows ac-coupling to the source. Using
capacitors in series with the termination resistors
Figure 82. 60-MHz Low-Pass Filter
allows the amplifier to self-bias both input and output
to midsupply.
Figure 81. THS4513 AC-Coupled Single-Supply
Low-Pass Filter
One application for the THS4513 is as a unity-gain
Figure 83. Low-Pass Filter Measured
buffer with low-pass filtering. Figure 82 shows a
Frequency Response
circuit that is driven by an ac-coupled 50-Ω source. A
1:1 transformer converts the differential output of the
THS4513 into a single-ended output capable of
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