LMH6518_15 Datasheet, PDF (31/41 Pages) Texas Instruments – LMH6518 900 MHz, Digitally Controlled, Variable Gain Amplifier

www.ti.com
LMH6518
SNOSB21C – MAY 2008 – REVISED JULY 2013
+5V
3,4
U1
LMH6518
16
+OUT Aux
1
-OUT Aux
2
5,8
V_{CM_Aux}
R₃
+5V ^{3.83 k:}
1%
+5V
R₁₁
237:
R₁₂
237:
R₁
R₂
75:
75:
+5V
6₊ ⁵ ₄
U2
1
LMH7220
-
3
2
R₁₀
100:
Trigger Output (LVDS)
R₄
1.20 k:
1%
+5V
U4 ^2.5V
LP3985
0-2.5V
SDA
SCL
V_A V_REF
U3
DAC101
C085
V_OUT
10 bit DAC
(I²C)
Figure 68. Single-Ended Trigger from LMH6518 Auxiliary Output
U2’s minimum Toggle Rate specification of 750 Mb/s with ±50 mV overdrive allow the oscilloscope to trigger on
repetitive waveforms well above the 500 MHz oscilloscope bandwidth applications, when the input signal is at
least 14.3% of FS swing
(= ^{50 mV} x 100)
0.7V
2
(17)
The worst case single event minimum discernable pulse width is set by the LMH7220’s propagation delay
specification of 3.63 ns (20 mV overdrive).
Both the Main and the Auxiliary outputs can recover gracefully and quickly from a 50% overdrive condition as
tabulated in Electrical Characteristics under overdrive Recovery Time. Overdrive conditions beyond 50%,
however, could result in longer recovery times due to the interaction between an internal clamp and the common
mode feedback loop that sets the output common mode voltage. This may have an impact on both the displayed
waveform and the oscilloscope Trigger. The result could be a loss of Trigger pulse and/or visual distortion of the
displayed waveform. To avoid this scenario, the oscilloscope should detect an excessive overdrive and go into
trigger-loss mode. Done this way, the oscilloscope display would show the last waveform that did not violate the
overdrive condition. Preferably there would be a visual indicator on the screen that alerts the user of the situation
so that he can correct the excessive condition to return to normal display.
Copyright © 2008–2013, Texas Instruments Incorporated
Product Folder Links: LMH6518
Submit Documentation Feedback
31