LMH2100 Datasheet, PDF (30/32 Pages) National Semiconductor (TI) – 50 MHz to 4 GHz 40 dB Logarithmic Power Detector for CDMA and WCDMA

nected to each other by multiple vias. The characteristic
impedance of the transmission line is mainly determined by
the width W and the distance S. In order to minimize reflec-
tions, the width W of the center trace should match the size
of the package pad. The required value for the characteristic
impedance can subsequently be realized by selection of the
proper gap width S.
30014081
FIGURE 16. GCPW Configuration
4.3 Reference REF
The Reference pin can be used to compensate for tempera-
ture drift of the internal reference voltage as described in
Section 3.4.2. The REF pin is directly connected to the in-
verting input of the transimpedance amplifier. Thus, RF sig-
nals and other spurious signals couple directly through to the
output. Introduction of RF signals can be prevented by con-
necting a small capacitor between the REF pin and ground.
The capacitor should be placed close to the REF pin as de-
picted in Figure 14.
4.4 Output OUT
The OUT pin is sensitive to crosstalk from the RF input, es-
pecially at high power levels. The ESD diode between the
output and V_DD may rectify the crosstalk, but may add an un-
wanted inaccurate DC component to the output voltage.
The board layout should minimize crosstalk between the de-
tectors input RF_IN and the detectors output. Using an addi-
tional capacitor connected between the output and the
positive supply voltage (V_DD pin) or GND can prevent this. For
optimal performance this capacitor should be placed as close
as possible to the OUT pin of the LMH2100.
www.national.com
30