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HSMS-282E-BLKG Datasheet(PDF) 6 Page - Agilent(Hewlett-Packard) |
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HSMS-282E-BLKG Datasheet(HTML) 6 Page - Agilent(Hewlett-Packard) |
6 / 14 page 6 RS is seen in a curve that droops at high current). All Schottky diode curves have the same slope, but not necessarily the same value of current for a given voltage. This is determined by the saturation current, IS, and is related to the barrier height of the diode. Through the choice of p-type or n-type silicon, and the selection of metal, one can tailor the characteristics of a Schottky diode. Barrier height will be altered, and at the same time CJ and RS will be changed. In general, very low barrier height diodes (with high values of IS, suitable for zero bias applica- tions) are realized on p-type silicon. Such diodes suffer from higher values of RS than do the n-type. 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 detectors used in gain or power control circuits. Detector Applications Detector circuits can be divided into two types, large signal (P in > -20 dBm) and small signal (P in < -20 dBm). In general, 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 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 imped- ance matching network 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 realized 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 Detec- tors. The series and shunt circuits can be combined into a voltage doubler[1], as shown in Figure 12. The doubler offers three advan- tages over the single diode circuit. 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 temperatures, the differential detector[2] is often used. 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 example the HSMS-2825 in Figure 13. In the Agilent assembly facility, the two dice in a surface mount package are taken from adjacent sites on the wafer (as illustrated in Figure 14). This [1] Agilent 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. |
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