bias
differential
amplifier
matching
network
HSMS-282P
Figure 14. Fabrication of Avago Diode Pairs.
Figure 17. Voltage Doubler Differential Detector.
In high power applications, coupling of RF energy from
the detector diode to the reference diode can introduce
error in the differential detector. The HSMS‑282K diode
pair, in the six lead SOT‑363 package, has a copper bar
between the diodes that adds 10 dB of additional isola‑
tion between them. As this part is manufactured in the
SOT‑363 package it also provides the benefit of being
40% smaller than larger SOT‑143 devices. The HSMS‑282K
is illustrated in Figure 15 — note that the ground connec‑
tions must be made as close to the package as possible to
minimize stray inductance to ground.
detector diode
However, care must be taken to assure that the two refer‑
ence diodes closely match the two detector diodes. One
possible configuration is given in Figure 16, using two
HSMS‑2825. Board space can be saved through the use of
the HSMS‑282P open bridge quad, as shown in Figure 17.
While the differential detector works well over tempera‑
ture, another design approach
[3]
works well for large signal
detectors. See Figure 18 for the schematic and a physical
layout of the circuit. In this design, the two 4.7 KΩ resis‑
tors and diode D2 act as a variable power divider, assuring
constant output voltage over temperature and improving
output linearity.
RF
in
68
Ω
PA
V
bias
D1
4.7 KΩ
33 pF
V
o
4.7 KΩ
D2
68
Ω
33 pF
HSMS-282K
reference diode
to differential amplifier
HSMS-2825
or
HSMS-282K
RF
in
HSMS-282K
Figure 15. High Power Differential Detector.
V
o
4.7 KΩ
The concept of the voltage doubler can be applied to the
differential detector, permitting twice the output voltage
for a given input power (as well as improving input im‑
pedance and suppressing second harmonics).
bias
Figure 18. Temperature Compensated Detector.
differential
amplifier
HSMS-2825
matching
network
HSMS-2825
In certain applications, such as a dual‑band cellphone
handset operating at both 900 and 1800 MHz, the second
harmonics generated in the power control output detec‑
tor when the handset is working at 900 MHz can cause
problems. A filter at the output can reduce unwanted
emissions at 1800 MHz in this case, but a lower cost so‑
lution is available
[4]
. Illustrated schematically in Figure
19, this circuit uses diode D2 and its associated passive
components to cancel all even order harmonics at the
detector’s RF input. Diodes D3 and D4 provide tempera‑
ture compensation as described above. All four diodes are
contained in a single HSMS‑ 282R package, as illustrated
in the layout shown in Figure 20.
[3] Hans Eriksson and Raymond W. Waugh, “A Temperature Compensated
Linear Diode Detector,” to be published.
Figure 16. Voltage Doubler Differential Detector.
7
AVAGO [ AVAGO TECHNOLOGIES LIMITED ]
