8
lower cost solution 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 temperature compensa-
tion as described above. All four
diodes are contained in a single
HSMS- 282R package, as illus-
trated in the layout shown in
Figure 20.
Mixer applications
The HSMS-282x family, with its
wide variety of packaging, can be
used to make excellent mixers at
frequencies up to 6 GHz.
The HSMS-2827 ring quad of
matched diodes (in the SOT-143
package) has been designed for
double balanced mixers. The
smaller (SOT-363) HSMS-282R ring
quad can similarly be used, if the
quad is closed with external
connections as shown in Figure 21.
RF in
68
Ω
D2
R3
D1
R1
V+
R2
HSMS-282R
V–
C2
R4
C1
D3
LO in
RF in
A review of Figure 21 may lead to
the question as to why the
HSMS-282R ring quad is open on
the ends. Distortion in double
balanced mixers can be reduced
if LO drive is increased, up to the
point where the Schottky diodes
are driven into saturation. Above
this point, increased LO drive will
not result in improvements in
distortion. The use of expensive
high barrier diodes (such as those
fabricated on GaAs) can take
advantage of higher LO drive
power, but a lower cost solution
is to use a eight (or twelve) diode
ring quad. The open design of the
HSMS-282R permits this to easily
be done, as shown in Figure 23.
D4
C1 = C2
≈
100 pF
R1 = R2 = R3 = R4 = 4.7 KΩ
D1 & D2 & D3 & D4 = HSMS-282R
IF out
LO in
Figure 21. Double Balanced
Mixer.
RF in
Figure 19. Schematic of Sup-
pressed Harmonic Detector.
HSMS-282R
4.7 KΩ
V+
100 pF
4.7 KΩ
V–
100 pF
RF in
68
Ω
Both of these networks require a
crossover or a three dimensional
circuit. A planar mixer can be
made using the SOT-143 cross-
over quad, HSMS-2829, as shown
in Figure 22. In this product, a
special lead frame permits the
crossover to be placed inside the
plastic package itself, eliminating
the need for via holes (or other
measures) in the RF portion of
the circuit itself.
HSMS-2829
HSMS-282R
IF out
Figure 23. Low Distortion Double
Balanced Mixer.
This same technique can be used
in the single-balanced mixer.
Figure 24 shows such a mixer,
with two diodes in each spot
normally occupied by one. This
mixer, with a sufficiently high LO
drive level, will display low
distortion.
RF in
180°
hybrid
LO in
HSMS-282R
Low pass
filter
Figure 20. Layout of Suppressed
Harmonic Detector.
Note that the forgoing discussion
refers to the output voltage being
extracted at point V+ with
respect to ground. If a differential
output is taken at V+ with respect
to V-, the circuit acts as a voltage
doubler.
LO in
RF in
IF out
Figure 24. Low Distortion Bal-
anced Mixer.
IF out
Figure 22. Planar Double Bal-
anced Mixer.
[4]
Alan Rixon and Raymond W. Waugh, “A Suppressed Harmonic Power Detector for Dual
Band ‘Phones,” to be published.
AGILENT [ AGILENT TECHNOLOGIES, LTD. ]
