8

Both of these networks require a crossover or a three di‑

mensional circuit. A planar mixer can be made using the

SOT‑143 crossover quad, HSMS‑2829, as shown in Figure

22. In this product, a special lead frame permits the cross‑

over to be placed inside the plastic package itself, elimi‑

nating the need for via holes (or other measures) in the RF

portion of the circuit itself.

Figure 20. Layout of Suppressed Harmonic Detector.

Figure 19. Schematic of Suppressed Harmonic Detector.

Note that the forgoing discussion refers to the output volt‑

age 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.

Figure 21. Double Balanced Mixer.

Figure 22. Planar Double Balanced Mixer.

RF in

D1

R1

V+

R2

D3

C1

V–

R4

D4

C1 = C2 ª 100 pF

R1 = R2 = R3 = R4 = 4.7 K

D1 & D2 & D3 & D4 = HSMS-282R

C2

D2

68

R3

HSMS-282R

4.7 K

4.7 K

100 pF

100 pF

68

V–

RF in

V+

HSMS-282R

IF out

RF in

LO in

HSMS-2829

IF out

RF in

LO in

Note 4. Alan Rixon and Raymond W. Waugh, “A Suppressed Harmonic Power Detector for Dual Band ‘Phones,” to be published.

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 con‑

nections as shown in Figure 21.

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.

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.

Figure 24. Low Distortion Balanced Mixer.

HSMS-282R

IF out

RF in

LO in

HSMS-282R

180

hybrid

IF out

LO in

RF in

Low pass

filter