LMH6881 Datasheet, PDF (22/35 Pages) Texas Instruments – Small Signal Bandwidth: 2400 MHz

LMH6881
SNOSC72F – JUNE 2012 – REVISED FEBRUARY 2015
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50:
INPS
R_IN = 50:
LMH6881
N/C INPD
N/C _INMD
INMS
50:
+2.5V
ROUT
LPF
50:
VCM = 2.5V
50:
ROUT
RT
75:
VCM =1.5V
300:
RL
ADC
75:
RT
OCM
+1.25V
Parallel termination = 2* RT || RL = 150 || 300 =
100:
VCM voltage divider = 2.5V * RT/(ROUT + RT) =
2.5 * 75/125 = 1.5 V
Figure 45. DC-Coupled ADC Driver Example 1, High-Input Impedance ADC
LMH6881
N/C
INSP
INDP
100:
INDM
N/C ^INSM
OUTM
ROUT
OUTP
100:
V =2.5V
100:
ROUT
OCM
100:
RT
V=1.25V ADC12D1800RF
CM
100:
RT
+1.25V
Figure 46. DC-Coupled ADC Driver Example 2, Terminated Input ADC
8.1.4 Figure of Merit: Dynamic Range Figure
The dynamic range figure (DRF) as illustrated in Figure 4, is defined as the input third order intercept point (IIP3)
minus the noise figure (NF). The combination of noise figure and linearity gives a good proxy for the total
dynamic range of an amplifier. In some ways this figure is similar to the SFDR of an analog-to-digital converter.
In contrast to an ADC, though, an amplifier will not have a full-scale input to use as a reference point. With
amplifiers, there is no one point where signal amplitude hits “full scale”. Yet, there are real limitations to how
large of a signal the amplifier can handle. Normally, the distortion products produced by the amplifier will
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