LMH6555_14 Datasheet, PDF (15/37 Pages) Texas Instruments – LMH6555 Low Distortion 1.2 GHz Differential Driver

LMH6555
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SNOSAJ1C – NOVEMBER 2006 – REVISED MARCH 2011
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2. Calculate each input pin swing to be ½ the swing determined in step 1:
V_IN+ = V_IN− = V_{IN_DIFF}/ 2
(15)
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For Figure 27
V_IN+ = V_IN− = 131.5 mV_PP/ 2 = 65.7 mV_PP
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3. 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)
(16)
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For Figure 27:
R_S = 50Ω → V_{I_CM} = 15.75 / (R_S+ 64)
V_{I_CM} = 15.75/ (50+64) = 138.2 mV
(17)
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4. Calculate V_OUT knowing the Insertion Gain (A_{V_DIFF}):
V_OUT = (V_IN · / 2) · A_{V_DIFF}
A_{V_DIFF} = 2 · R_F/ (2R_S + R_{IN_DIFF})
where
• R_F= 430Ω
• R_{IN_DIFF} = 78Ω
(18)
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For Figure 27:
R_S = 50Ω → A_{V_DIFF} = 4.83 V/V
V_OUT = (0.3 V_PP/2) · 4.83 V/V= 724.5 mV_PP
(19)
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The values determined with the procedure outlined here are shown in Figure 28.
0.3
65.7 mV_PP @
V_{IN- 138 mV DC VIN+}
0.2
0.1
0
V₁
-0.1
V₂
-0.2
-0.3
TIME
Figure 28. Input Voltage for Figure 27 Schematic
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