HSMS282X datasheet(7/14 Pages) HP

7 / 14 page

assures that the characteristics of

the two diodes are more highly

matched than would be possible

through individual testing and

hand matching.

matching

network

differential

amplifier

HSMS-2825

bias

Figure 13. Differential Detector.

Figure 14. Fabrication of Agilent

Diode Pairs.

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

isolation 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

connections must be made as

close to the package as possible

to minimize stray inductance to

ground.

detector diode

reference diode

to differential amplifier

Vbias

HSMS-282K

Figure 15. High Power Differential

Detector.

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 impedance and

suppressing second harmonics).

However, care must be taken to

assure that the two reference

diodes closely match the two

detector diodes. One possible

configuration is given in Fig-

ure 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.

matching

network

differential

amplifier

HSMS-2825

bias

Figure 16. Voltage Doubler

Differential Detector.

differential

amplifier

HSMS-282P

bias

matching

network

Figure 17. Voltage Doubler

Differential Detector.

While the differential detector

works well over temperature,

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 K

Ω resistors and diode D2 act

as a variable power divider,

assuring constant output voltage

over temperature and improving

output linearity.

33 pF

HSMS-2825

HSMS-282K

4.7 K

Ω

33 pF

4.7 K

Ω

4.7 K

Ω

RFin

Figure 18. Temperature Compensated

Detector.

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 detector 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

[3] Hans Eriksson and Raymond W. Waugh, “A Temperature Compensated Linear Diode

Detector,” to be published.

88759/02-5.PM6.0J

2001.04.25, 6:41 PM

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