THS4500-EP Datasheet, PDF (22/38 Pages) National Semiconductor (TI) – WIDEBAND, LOW-DISTORTION, FULLY DIFFERENTIAL AMPLIFIER

THS4500-EP
SLOS832 – JUNE 2013
R_S
V_S
R_G1
R_T
V_OCM
R_F1
+V_S
+_-
-⁺
R_G2
R_F2
Figure 99. Application Circuit for the THS4500
and THS4501, Featuring Single-Supply Operation
With a Ground-Reference Input Signal
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V _OUT)
+
V_IN)(1–β)–V_IN–(1–β) ) 2V_OCMβ
2β
(1)
V _OUT–
+
–V_IN)(1–β) ) V_IN–(1–β) ) 2V_OCMβ
2β
(2)
V_N + V_IN–(1–β) ) V_OUT)β
(3)
Where:
β
+
R_F
R_G
) R_G
(4)
V_P + V_IN)(1–β) ) V_OUT–β
NOTE: The equations denote the device inputs as V_N and V_P, and
the circuit inputs as V_IN+ and V_IN–.
(5)
R_S
R_G1
R_F1
V_S
R_T
+V_S
+_-
V_OCM
-⁺
-V_S
R_G2
R_F2
Figure 100. Application Circuit for the THS4500
and THS4501, Featuring Split-Supply Operation
With an Input Signal Referenced at the Midrail
Equation 1 through Equation 5 are used to calculate
the required input common-mode range for a given
set of input conditions.
The equations allow calculation of the input common-
mode range requirements, given information about
the input signal, the output voltage swing, the gain,
and the output common-mode voltage. Calculating
the maximum and minimum voltage required for V_N
and V_P (the amplifier input nodes) determines
whether or not the input common-mode range is
violated or not. Four equations are required: two
calculate the output voltages and two calculate the
node voltages at V_N and V_P (note that only one of
these nodes needs calculation, because the amplifier
forces a virtual short between the two nodes).
R_G
R_F
V_IN+
V_IN-
V_P
V_OCM
+_-
-⁺
V_N
R_G
R_F
V_OUT-
V_OUT+
Figure 101. Diagram For Input Common-Mode
Range Equations
Table 1 and Table 2 depict the input common-mode
range requirements for two different input scenarios,
an input referenced around the negative rail and an
input referenced around midrail. The tables highlight
the differing requirements on input common-mode
range, and illustrate the reasoning to choose either
the THS4500/1 or the THS4502/3. For signals
referenced around the negative power supply, the
THS4500/1 should be chosen because its input
common-mode range includes the negative supply
rail. For all other situations, the THS4502/3 offers
slightly improved distortion and noise performance for
applications with input signals centered between the
power-supply rails.
Gain
(V/V)
1
2
4
8
V_IN+
(V)
–2.0 to 2.0
–1.0 to 1.0
–0.5 to 0.5
–0.25 to 0.25
Table 1. Negative-Rail Referenced
V_IN–
(V)
0
V_IN
(V_PP)
4
0
2
0
1
0
0.5
V_OCM
(V)
2.5
2.5
2.5
2.5
V_OD
(V_PP)
4
4
4
4
V_NMIN
(V)
0.75
0.5
0.3
0.167
V_NMAX
(V)
1.75
1.167
0.7
0.389
22
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