Datasheet HSMS-282x (Broadcom) - 6

Thus, p‑type diodes are generally reserved for detector • The two diodes are in parallel in the RF circuit, lowering applications (where very high values of R swamp out the input impedance and making the design of the RF V high R ) and n‑type diodes such as the HSMS‑282x are matching network easier. S used for mixer applications (where high L.O. drive levels • The two diodes are in series in the output (video) keep R low). DC biased detectors and self‑biased detec‑ V circuit, doubling the output voltage. tors used in gain or power control circuits. • Some cancellation of even‑order harmonics takes place
Detector Applications
at the input. Detector circuits can be divided into two types, large signal (P > ‑20 dBm) and small signal (P < ‑20 dBm). In general,
DC Bias
in in the former use resistive impedance matching at the input to improve flatness over frequency—this is possible since the input signal levels are high enough to produce ade‑ quate output voltages without the need for a high Q reac‑ tive input matching network. These circuits are self‑biased
Zero Biased Diodes DC Biased Diodes
(no external DC bias) and are used for gain and power
Figure 12. Voltage Doubler.
control of amplifiers. Small signal detectors are used as very low cost receivers, The most compact and lowest cost form of the doubler is and require a reactive input impedance matching net‑ achieved when the HSMS‑2822 or HSMS‑282C series pair work to achieve adequate sensitivity and output voltage. is used. Those operating with zero bias utilize the HSMS‑ 285x family of detector diodes. However, superior performance Both the detection sensitivity and the DC forward voltage over temperature can be achieved with the use of 3 to 30 of a biased Schottky detector are temperature sensitive. µA of DC bias. Such circuits will use the HSMS‑282x family Where both must be compensated over a wide range of of diodes if the operating frequency is 1.5 GHz or lower. temperatures, the differential detector[2] is often used. Such a circuit requires that the detector diode and the Typical performance of single diode detectors (using reference diode exhibit identical characteristics at all DC HSMS‑2820 or HSMS‑282B) can be seen in the transfer bias levels and at all temperatures. This is accomplished curves given in Figures 7 and 8. Such detectors can be re‑ through the use of two diodes in one package, for exam‑ alized either as series or shunt circuits, as shown in Figure ple the HSMS‑2825 in Figure 13. In the Avago assembly 11. facility, the two dice in a surface mount package are taken from adjacent sites on the wafer (as illustrated in Figure
DC Bias
14). This assures that the characteristics of the two diodes are more highly matched than would be possible through individual testing and hand matching.
Shunt inductor provides RF in video signal return RF Shunt diode provides impedance R R DC Bias M L differential video signal return matching Video out amplifier network +3V RL Zero Biased Diodes DC Biased Diodes Figure 11. Single Diode Detectors. Figure 13. Differential Detector.
The series and shunt circuits can be combined into a volt‑ age doubler[1], as shown in Figure 12. The doubler offers three advantages over the single diode circuit. Notes: 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. 6