LMH2110 Datasheet, PDF (23/33 Pages) National Semiconductor (TI) – 8 GHz Logarithmic RMS Power Detector with 45 dB Dynamic Range

LMH2110
www.ti.com
SNWS022C – JANUARY 2010 – REVISED MARCH 2013
and is described by:
V_OUT = K_SLOPE (P_IN – P_INT)
where
• K_SLOPE is the slope of the line in mV/dB
• P_IN the input power level
• P_INT is the power level in dBm at which the line intercepts V_OUT = 0V (See Figure 52).
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2.4
Ideal
LOG function
2.0
1.6
1.2
0.8
P_INT
0.4
Detector
response
K_SLOPE
0.0
-50
-30 -20 -10 0 10
RF INPUT POWER (dBm)
Figure 52. Ideal Logarithmic Response
To determine the log conformance error two steps are required:
1. Determine the best fitted line at 25°C.
2. Determine the difference between the actual data and the best fitted line.
The best fit can be determined by standard routines. A careful selection of the fit range is important. The fit range
should be within the normal range of operation of the device. Outcome of the fit is K_SLOPE and P_INT.
Subsequently, the difference between the actual data and the best fitted line is determined. The log conformance
is specified as an input referred error. The output referred error is therefore divided by the K_SLOPE to obtain the
input referred error. The log conformance error is calculated by the following equation:
V_OUT
E_LC =
K_{SLOPE 25qC} (P_IN
K_{SLOPE 25qC}
P_{INT 25qC})
where
• V_OUT is the measured output voltage at a power level at P_IN at a temperature. K_{SLOPE 25°C} (mV/dB)
• P_{INT 25°C} (dBm) are the parameters of the best fitted line of the 25°C transfer
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In Figure 53 it can be seen that both the error with respect to the ideal LOG response as well as the error due to
temperature variation are included in this error metric. This is because the measured data for all temperatures is
compared to the fitted line at 25°C. The measurement result of a typical LMH2110 in Figure 53 shows a dynamic
range of 36 dB for E_LC= ±1dB.
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