Datasheet

V
S+
CM
V
Signal
V
S-
R
F
R
F
R
G
R
G
R
T
R
O
R
O
V
OUT+
V
OUT-
THS 4513
R
S
R
T
R
S
V
S+
V
S+
R
PU
R
PU
( )
÷
÷
ø
ö
ç
ç
è
æ
+-
÷
÷
ø
ö
ç
ç
è
æ
-
=
+
FIN
IC
F
CM
SIC
PU
R
1
R
1
V
R
1
V
VV
R
V
S+
CM
V
S–
50kW
tointernal
CMcircuit
I
EXT
50kW
V
OUT-
V
S+
R
F
R
F
R
G
R
G
R
T
G=1
R
O
R
O
R
T
R
S
V
SIGNAL
R
S
V
S-
V
OUT+
V
CM
V
CM
V
BIAS
= V
CM
V
CM
V
CM
+
-
Wideband
CM
THS4513
Buffer
( )
W
--
=
-+
k50
VVV2
I
SSCM
EXT
THS4513
SLOS472E –AUGUST 2005–REVISED JANUARY 2013 www.ti.com
Setting the Output Common-Mode Voltage
In Figure 79, the signal source is referenced to a
voltage derived from the CM pin via a unity-gain
The output common-mode voltage is set by the
wideband buffer such as the BUF602. V
CM
is set to
voltage at the CM pin(s). The internal common-mode
midsupply by THS4513 internal circuitry. R
T
along
control circuit maintains the output common-mode
with the input impedance of the amplifier provides
voltage within 3-mV offset (typ) from the set voltage,
input termination, which is also referenced to V
CM
.
when set within 0.5 V of midsupply, with less than 4-
mV differential offset voltage. If left unconnected, the
Note that R
S
and R
T
are added to the alternate input
common-mode set point is set to midsupply by
from the signal input to balance the amplifier.
internal circuitry, which may be over-driven from an
Alternately, one resistor can be used equal to the
external source. Figure 78 is representative of the
combined value R
G
+ R
S
|| R
T
on this input. This
CM input. The internal CM circuit has about 700 MHz
technique is also true of the circuits shown in
of –3-dB bandwidth, which is required for best
Figure 80 and Figure 81.
performance, but it is intended to be a dc bias input
pin. Bypass capacitors are recommended on this pin
to reduce noise at the output. The external current
required to overdrive the internal resistor divider is
given by Equation 2:
(2)
where V
CM
is the voltage applied to the CM pin.
Figure 79. THS4513 DC-Coupled Single-Supply
with Input Biased to V
CM
In Figure 80, the source is referenced to ground and
so is the input termination resistor. R
PU
is added to
the circuit to avoid violating the V
ICR
of the op amp.
The proper value of resistor to add can be calculated
from Equation 3:
Figure 78. CM Input Circuit
(3)
Single-Supply Operation (3 V to 5 V)
To facilitate testing with common lab equipment, the
THS4513 EVM allows split-supply operation, and the
characterization data presented in this data sheet
were taken with split-supply power inputs. The device
can easily be used with a single-supply power input
without degrading the performance. Figure 79,
Figure 80, and Figure 81 show dc and ac-coupled
single-supply circuits with single-ended inputs. These
configurations all allow the input and output common-
mode voltage to be set to midsupply allowing for
optimum performance. The information presented
here can also be applied to differential input sources.
Figure 80. THS4513 DC-Coupled Single-Supply
with R
PU
Used to Set V
IC
26 Submit Documentation Feedback Copyright © 2005–2013, Texas Instruments Incorporated
Product Folder Links: THS4513