LMH2110_15 Datasheet, PDF (27/36 Pages) Texas Instruments – LMH2110 8-GHz Logarithmic RMS Power Detector with 45-dB Dynamic Range

www.ti.com
8.2.1.3 Application Curves
2.4
2.0
5.8 GHz
3.5 GHz
1.6
1.9 GHz
900 MHz
1.2
50 MHz
0.8
0.4
8 GHz
0.0
-40 -30 -20 -10
0
10
RF INPUT POWER (dBm)
Figure 52. Output Voltage vs. RF Input Power
LMH2110
SNWS022D – JANUARY 2010 – REVISED JUNE 2015
2.00
1.75
1.50
1.25
RF_IN = 0 dBm
RF_IN = -5 dBm
RF_IN = -10 dBm
1.00
RF_IN = -15 dBm
0.75
RF_IN = -20 dBm
0.50
RF_IN = -25 dBm
0.25
0.00
10M
100M
1G
10G
FREQUENCY (Hz)
Figure 53. Output Voltage vs. Frequency
8.2.2 Application With Resistive Divider
RF systems typically use a characteristic impedance of 50 Ω. The LMH2110 is no exception to this. The RF input
pin of the LMH2110 has an input impedance of 50 Ω. It enables an easy, direct connection to a directional
coupler without the need for additional components (Figure 44). For an accurate power measurement the input
power range of the LMH2110 needs to be aligned with the output power range of the power amplifier. This can
be done by selecting a directional coupler with the correct coupling factor.
Because the LMH2110 has a constant input impedance, a resistive divider can also be used instead of a
directional coupler (Figure 54).
RF
PA
ANTENNA
R₁
V_DD
RF_IN
A1
OUT
B1
A2
LMH2110
EN C2
B2, C1
GND
ADC
Figure 54. Application With Resistive Divider
Resistor R₁ implements an attenuator together with the detector input impedance to match the output range of
the PA to the input range of the LMH2110. The attenuation (A_dB) realized by R₁ and the effective input
impedance of the LMH2110 equals:
ª ^R1 º
A_dB
=
20LOG
«1
¬
+
R_IN
»
¼
(16)
Copyright © 2010–2015, Texas Instruments Incorporated
Product Folder Links: LMH2110
Submit Documentation Feedback
27