LMH2100 Datasheet, PDF (34/49 Pages) National Semiconductor (TI) – 50 MHz to 4 GHz 40 dB Logarithmic Power Detector for CDMA and WCDMA

LMH2100
SNWS020C – NOVEMBER 2007 – REVISED OCTOBER 2015
Typical Applications (continued)
8.2.1.1 Design Requirements
Some of the design requirements for this logarithmic RMS power detector include:
Table 1. Design Parameters
DESIGN PARAMETER
Supply voltage
RF input frequency (unmodulated continuous wave)
Minimum power level
Maximum power level
Maximum output voltage
EXAMPLE VALUE
2.7 V
1855 MHz
0 dBm
–5 dBm
2V
www.ti.com
8.2.1.2 Detailed Design Procedure
8.2.1.2.1 Detector Interfacing
For optimal performance of the LMH2100, it is important that all its pins are connected to the surrounding
circuitry in the appropriate way. This section discusses guidelines and requirements for the electrical connection
of each pin of the LMH2100 to ensure proper operation of the device. Starting from a block diagram, the function
of each pin is elaborated. Subsequently, the details of the electrical interfacing are separately discussed for each
pin. Special attention will be paid to the output filtering options and the differences between single ended and
differential interfacing with an ADC.
8.2.1.2.1.1 Concept of Power Measurements
Power measurement systems generally consists of two clearly distinguishable parts with different functions:
1. A power detector device, that generates a DC output signal (voltage) in response to the power level of the
(RF) signal applied to its input.
2. An “estimator” that converts the measured detector output signal into a (digital) numeric value representing
the power level of the signal at the detector input.
A sketch of this conceptual configuration is depicted in Figure 80.
P_IN
F_DET ^VOUT
F_EST
MODEL
P_EST
PARAMETERS
Figure 80. Generic Concept of a Power Measurement System
The core of the estimator is usually implemented as a software algorithm, receiving a digitized version of the
detector output voltage. Its transfer F_EST from detector output voltage to a numerical output should be equal to
the inverse of the detector transfer F_DET from (RF) input power to DC output voltage. If the power measurement
system is ideal, that is, if no errors are introduced into the measurement result by the detector or the estimator,
the measured power P_EST - the output of the estimator - and the actual input power P_IN should be identical. In
that case, the measurement error E, the difference between the two, should be identically zero:
E = P_EST - P_IN { 0
œ P_EST = F_EST[F_DET(P_IN)] = P_IN
œ F_EST(V_OUT) = F_D-1ET(V_OUT)
(12)
34
Submit Documentation Feedback
Product Folder Links: LMH2100
Copyright © 2007–2015, Texas Instruments Incorporated