MT-076 Datasheet, PDF (1/9 Pages) Analog Devices – Differential Driver Analysis

Differential Driver Analysis
MT-076
TUTORIAL
Differential drivers can be driven by either single-ended or differential signals. This tutorial
analyzes both conditions using either an unterminated or a terminated source.
CASE 1: DIFFERENTIAL INPUT, UNTERMINATED SOURCE
Figure 1 shows a differential driver driven from a balanced unterminated source. This would
typically be the condition for a low impedance source where the connection distance between the
source and the driver is minimal.
R_F1
+
V_SIG/2
–
V_{ICM +}
V_SIG/2
–
R_S/2
V_IN
R_S/2
R_G1
V_OCM
R_G2
+
–
R_F2
– ^VOUT–
V_OUT
+
V_OUT+
R_G1 = R_G2
R_F1 = R_F2
G = ^VOUT = ^{VOUT+ − VOUT−} =
R _F1
V_IN
V_SIG
R_G1 + R_S / 2
Figure 1: Differential Input, Unterminated Source
The design inputs are the source impedance R_S, the gain setting resistor R_G1, and the desired gain
G. Note that the gain is measured with respect to the signal voltage source, V_SIG.
The total value of the gain setting resistor with respect to the signal source, V_SIG, is R_G1 + R_S/2.
Also, R_G2 = R_G1.
The required value of the feedback resistors, R_F1 = R_F2, is then calculated using:
R _F1
=
R _F2
=
G_⎜⎛
⎝
R
G1
+
R_S
2
⎟⎞
⎠
Eq. 1
Rev.0, 10/08, WK
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