lmh2120umx National Semiconductor Corporation, lmh2120umx Datasheet - Page 23

• Manufacturer Part Number: lmh2120umx
• Description: Lmh2120 6 Ghz Linear Rms Power Detector With 40 Db Dynamic Range
• Manufacturer: National Semiconductor Corporation

FIGURE 11. Graphical Representation of 10 dB Step Error
Figure 12
where a dynamic range of 35 dB is obtained for E
Variation due to Modulation
RMS power detectors, such as the LMH2120 are inherently
insensitive to different modulation schemes. This in contrast
to traditional detectors like peak detectors and LOG AMP de-
tectors, where modulation forms with high peak-to-average
ratios (PAR) can cause significant output variation. This is
because the measurement of these detectors is not an actual
RMS measurement and is therefore waveform dependent.
To be able to compare the various detector types on modu-
lation sensitivity, the variation due to modulation parameter is
used. To calculate the variation due to modulation (E
measurement result for an unmodulated RF carrier is sub-
tracted from the measurement result for a modulated RF
carrier. The calculations are similar to those for variation over
temperature. The variation due to modulation can be calcu-
lated by:
where V
plied power level of a modulated signal, V
E
OUT_MOD
MOD
shows the typical 10 dB step error at 1900 MHz,
FIGURE 12. 10 dB Step Error vs.
= (V
RF Input Power at 1900 MHz
is the measured output voltage for an ap-
OUT_MOD
Calculations
- V
OUT_CW
) / K
OUT_CW
SLOPE
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10dB
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is the output
MOD
= ±1dB.
), the
(17)
23
voltage as a result of an applied un-modulated signal having
the same power level.
Figure 13
where a E
-34 dBm to -2 dBm.
TEMPERATURE BEHAVIOR
The specified temperature range of the LMH2120 is from
-40°C to 85°C. The RF detector is, to a certain extent how-
ever, still functional outside these temperature limits. Fig-
ures 14, 15, 16 show the detector behavior for temperatures
from -50°C up to 125°C in steps of 25°C. The LMH2120 is still
very accurate within a dynamic range from -35 dBm to
5 dBm. On the upper and lower end the curves deviate in a
gradual way, the lowest temperature on the bottom side and
the highest temperature on top side.
FIGURE 13. Variation due to Modulation for W-CDMA at
FIGURE 14. V
shows the variation due to modulation for W-CDMA,
MOD
of 0.16 dB is obtained for a dynamic range from
OUT
vs. RF Input Power at 1900 MHz
1900 MHz
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