LMH2110_15 Datasheet, PDF (25/36 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
First the maximum sensitivity (S_MAX) is calculated per temperature by determining the maximum difference
between two output voltages for a 1-dB step within the power range:
S_MAX = V_{OUT P+1} – V_{OUT P}
(12)
To calculate the 1-dB step error an average sensitivity (S_AVG) is used which is the average of the maximum
sensitivity and an allowed minimum sensitivity (S_MIN). The allowed minimum sensitivity is determined by the
application. In this datasheet S_MIN = 30 mV/dB is used. Subsequently, the average sensitivity can be calculated
by:
S_AVG = (S_MAX + S_MIN) / 2
(13)
The 1-dB error is than calculated by:
E_{1 dB} = (S_ACTUAL - S_AVG) / S_AVG
where
• S_ACTUAL (actual sensitivity) is the difference between two output voltages for a 1-dB step at a given power
level.
(14)
Figure 48 shows the typical 1-dB step error at 1900 MHz, where a dynamic range of 38 dB over temperature is
obtained for E_1dB = ±0.3 dB.
2.0
1.5
1.0
25°C
85°C
0.5
0.0
-0.5
-40°C
-1.0
-1.5
-2.0
-40 -30 -20 -10
0
10
RF INPUT POWER (dBm)
Figure 48. 1-dB Step Error vs. RF Input Power at 1900 MHz
8.2.1.2.1.5 10-dB Step Error
This error is defined in a different manner than the 1-dB step error. This parameter shows the input power error
over temperature when a 10-dB power step is made. The 10-dB step at 25°C is taken as a reference.
To determine the 10-dB step error, first the output voltage levels (V1 and V2) for power levels P and P+10 dB” at
the 25°C are determined (Figure 49). Subsequently these 2 output voltages are used to determine the
corresponding power levels at temperature T (P_T and P_T + X). The difference between those two power levels
minus 10 results in the 10-dB step error.
25°C response
V2
Temp (T)
response
V1
RF_IN (dBm)
P P+10 dB
P_T
P_T+X
Figure 49. Graphical Representation of 10-dB Step Calculations
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