LMH2110_15 Datasheet, PDF (23/36 Pages) Texas Instruments – LMH2110 8-GHz Logarithmic RMS Power Detector with 45-dB Dynamic Range

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LMH2110
SNWS022D – JANUARY 2010 – REVISED JUNE 2015
The ideal linear-in-dB transfer is modeled by 2 parameters:
• Slope
• Intercept
and is described by Equation 9:
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 = 0 V (see Figure 45).
(9)
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 45. 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
must 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 Equation 10:
V_OUT K_{SLOPE 25GC} (P_IN P_{INT 25GC})
E_LC =
K_{SLOPE 25GC}
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.
(10)
In Figure 46 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 46 shows a dynamic range of
36 dB for E_LC = ±1 dB.
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