LMH2110 Datasheet, PDF (25/33 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
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}
(15)
For calculating 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
(16)
The 1dB 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
(17)
Figure 55 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 55. 1 dB Step Error vs. RF Input Power at 1900 MHz
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+10dB”
at the 25°C are determined (Figure 56). 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
subtracted by 10 results in the 10 dB step error.
Copyright © 2010–2013, Texas Instruments Incorporated
Product Folder Links: LMH2110
Submit Documentation Feedback
25