LMH6555_14 Datasheet, PDF (14/37 Pages) Texas Instruments – LMH6555 Low Distortion 1.2 GHz Differential Driver

LMH6555
SNOSAJ1C – NOVEMBER 2006 – REVISED MARCH 2011
For Figure 25:
V_IN− = 150 mV_PP - 131.4 mV_PP = 18.6 mV_PP
whitespace
6. Determine the DC average of the two inputs (V_{I_CM}) by using the following expression:
V_{I_CM} = 12.6 mA · R_E · R_S / (R_S + R_G + R_E)
where
• R_E = 25Ω
• R_G = 39Ω (both internal to the LMH6555)
For Figure 25
R_S = 50Ω → V_{I_CM} = 15.75 / (R_S + 64)
V_{I_CM} = 15.75/ (50+64) = 138.2 mV
whitespace
The values determined with the procedure outlined here are shown in Figure 26.
0.3
V_IN+
0.2
0.1
V_IN
0
150 mV_PP @
138 mV DC
V_IN-
18.6 mV_PP @
138 mV DC
-0.1
-0.2
-0.3
TIME
Figure 26. Input Voltage for Single-Ended Input Drive Schematic
www.ti.com
(10)
(11)
(12)
DIFFERENTIAL INPUT
The following is the procedure for determining the device operating conditions for differential input applications
using the Figure 27 schematic as an example.
R_S1
V₁
50: _VIN+
V_OUT-
LMH6555
V_IN-
V₂
R_S2
50:
R_L
100:
V_OUT+
Assuming transformer secondary, V_IN, of 300 mV_PP
Figure 27. Differential Input Drive
1. Calculate the swing across the input terminals (V_{IN_DIFF}) by considering the voltage division from the
differential source (V_IN) to the LMH6555 input terminals with differential input impedance R_{IN_DIFF}:
V_{IN_DIFF} = V_IN · R_{IN_DIFF}/ (2R_S + R_{IN_DIFF})
(13)
whitespace
For Figure 27:
V_{IN_DIFF} = 300 mV_PP · 78 / (100 + 78) = 131.5 mV_PP
(14)
14
Submit Documentation Feedback
Product Folder Links: LMH6555
Copyright © 2006–2011, Texas Instruments Incorporated