6

• The two diodes are in parallel in the RF circuit, lowering

the input impedance and making the design of the RF

matching network easier.

• The two diodes are in series in the output (video) circuit,

doubling the output voltage.

• Some cancellation of even‑order harmonics takes place

at the input.

DC Bias

DC Biased Diodes

Zero Biased Diodes

Figure 12. Voltage Doubler.

The most compact and lowest cost form of the doubler is

achieved when the HSMS‑2822 or HSMS‑282C series pair

is used.

Both the detection sensitivity and the DC forward voltage

of a biased Schottky detector are temperature sensitive.

Where both must be compensated over a wide range of

Such a circuit requires that the detector diode and the

reference diode exhibit identical characteristics at all DC

bias levels and at all temperatures. This is accomplished

through the use of two diodes in one package, for exam‑

ple the HSMS‑2825 in Figure 13. In the Avago assembly

facility, the two dice in a surface mount package are taken

from adjacent sites on the wafer (as illustrated in Figure

14). This 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.

[1] Avago Application Note 956‑4, “Schottky Diode Voltage Doubler.”

[2] Raymond W. Waugh, “Designing Large‑Signal Detectors for Handsets

and Base Stations,” Wireless Systems Design, Vol. 2, No. 7, July 1997,

pp 42 – 48.

Thus, p‑type diodes are generally reserved for detector

applications (where very high values of RV swamp out

high RS) and n‑type diodes such as the HSMS‑282x are

used for mixer applications (where high L.O. drive levels

keep RV low). DC biased detectors and self‑biased detec‑

tors used in gain or power control circuits.

Detector Applications

Detector circuits can be divided into two types, large signal

(P

the former use resistive impedance matching at the in‑

put to improve flatness over frequency—this is possible

since the input signal levels are high enough to produce

adequate output voltages without the need for a high Q

reactive input matching network. These circuits are self‑

biased (no external DC bias) and are used for gain and

power control of amplifiers.

Small signal detectors are used as very low cost receivers,

and require a reactive input impedance matching net‑

work to achieve adequate sensitivity and output voltage.

Those operating with zero bias utilize the HSMS‑ 285x

family of detector diodes. However, superior performance

over temperature can be achieved with the use of 3 to 30

µA of DC bias. Such circuits will use the HSMS‑282x family

of diodes if the operating frequency is 1.5 GHz or lower.

Typical performance of single diode detectors (using

HSMS‑2820 or HSMS‑282B) can be seen in the transfer

curves given in Figures 7 and 8. Such detectors can be re‑

alized either as series or shunt circuits, as shown in Figure

11.

DC Bias

Shunt inductor provides

video signal return

Shunt diode provides

video signal return

DC Bias

DC Biased Diodes

Zero Biased Diodes

Figure 11. Single Diode Detectors.

The series and shunt circuits can be combined into a volt‑

three advantages over the single diode circuit.