LMH2110_15 Datasheet, PDF (26/36 Pages) Texas Instruments – LMH2110 8-GHz Logarithmic RMS Power Detector with 45-dB Dynamic Range

LMH2110
SNWS022D – JANUARY 2010 – REVISED JUNE 2015
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Figure 50 shows the typical 10-dB step error at 1900 MHz, where a dynamic range of 30 dB is obtained for
E_10dB = ±1 dB.
2.0
1.5
1.0
85°C
0.5
0.0
-0.5
-40°C
-1.0
-1.5
-2.0
-40 -35 -30 -25 -20 -15 -10 -5 0
RF INPUT POWER (dBm)
Figure 50. 10 dB Step Error vs. RF Input Power at 1900 MHz
8.2.1.2.1.6 Variation Due to Modulation
The response of an RF detector may vary due to different modulation schemes. How much it varies depends on
the modulation form and the type of detector. Modulation forms with high peak-to-average ratios (PAR) can
cause significant variation, especially with traditional RF detectors. This is because the measurement is not an
actual RMS measurement and is therefore waveform dependent.
To calculate the variation due to modulation (E_MOD), the measurement result for an un-modulated RF carrier is
subtracted from the measurement result of a modulated RF carrier. The calculations are similar to those for
variation over temperature. The variation due to modulation can be calculated by:
E_MOD = (V_{OUT_MOD} – V_{OUT_CW}) / K_SLOPE
where
• V_{OUT_MOD} is the measured output voltage for an applied power level of a modulated signal.
• V_{OUT_CW} is the output voltage as a result of an applied un-modulated signal having the same power level. (15)
Figure 51 shows the variation due to modulation for W-CDMA, where a E_MOD of 0.09 dB in obtained for a
dynamic range from –38 dBm to –5 dBm.
1.5
1.0
W-CDMA, REL8
0.5
0.0
W-CDMA, REL6
-0.5
W-CDMA, REL7
-1.0
-1.5
-40 -30 -20 -10
0
10
RF INPUT POWER (dBm)
Figure 51. Variation Due to Modulation for W-CDMA
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