HSMS-285x Series Surface Mount Zero Bias Schottky Detector Diodes Data Sheet Description Features Avago's HSMS-285x family of zero bias Schottky detector diodes has been designed and optimized for use in small signal (Pin <-20 dBm) applications at frequencies below 1.5 GHz. They are ideal for RF/ID and RF Tag applications where primary (DC bias) power is not available. * Surface Mount SOT-23/SOT143 Packages Important Note: For detector applications with input power levels greater than -20 dBm, use the HSMS-282x series at frequencies below 4.0 GHz, and the HSMS-286x series at frequencies above 4.0 GHz. The HSMS-285x series IS NOT RECOMMENDED for these higher power level applications. Available in various package configurations, these detector diodes provide low cost solutions to a wide variety of design problems. Avago's manufacturing techniques assure that when two diodes are mounted into a single package, they are taken from adjacent sites on the wafer, assuring the highest possible degree of match. * Miniature SOT-323 and SOT363 Packages * High Detection Sensitivity: up to 50 mV/W at 915 MHz * Low Flicker Noise: -162 dBV/Hz at 100 Hz * Low FIT (Failure in Time) Rate* * Tape and Reel Options Available * Matched Diodes for Consistent Performance * Better Thermal Conductivity for Higher Power Dissipation * Lead-free * For more information see the Surface Mount Schottky Reliability Data Sheet. Attention: Observe precautions for handling electrostatic sensitive devices. ESD Machine Model (Class A) ESD Human Body Model (Class 0) Refer to Avago Application Note A004R: Electrostatic Discharge Damage and Control. Pin Connections and Package Marking 6 PLx 1 2 3 5 4 SOT-363 Package Lead Code Identification (top view) Notes: 1. Package marking provides orientation and identification. 2. See "Electrical Specifications" for appropriate package marking. SOT-23/SOT-143 Package Lead Code Identification (top view) SINGLE 3 UNCONNECTED TRIO 6 5 1 2 SERIES 3 L 4 6 3 1 BRIDGE QUAD 5 2 4 P 3 SOT-323 Package Lead Code Identification (top view) 1 #0 2 1 #2 UNCONNECTED PAIR 3 4 1 #5 2 2 SINGLE 3 SERIES 3 1 1 B 2 C 2 SOT-23/SOT-143 DC Electrical Specifications, TC = +25C, Single Diode Part Number HSMS- Package Marking Lead Code Code Configuration Maximum Forward Voltage VF (mV) Maximum Reverse Leakage, IR (A) 2850 P0 0 Single 150 250 175 2852 P2 2 Series Pair [1,2] 2855 P5 5 Unconnected Pair[1,2] Test IF = 0.1 mA IF = 1.0 mA VR=2V Conditions Typical Capacitance CT (pF) 0.30 VR = -0.5 V to -1.0V f = 1 MHz Notes: 1. VF for diodes in pairs is 15.0 mV maximum at 1.0 mA. 2. CT for diodes in pairs is 0.05 pF maximum at -0.5V. SOT-323/SOT-363 DC Electrical Specifications, TC = +25C, Single Diode Part Package Number Marking Lead HSMSCode Code Configuration Maximum Forward Voltage VF (mV) Maximum Reverse Typical Leakage, Capacitance IR (A) CT (pF) 285B P0 B Single 150 250 175. 285C P2 C Series Pair 285L PL L Unconnected Trio 285P PP P Bridge Quad Test IF = 0.1 mA IF = 1.0 mA VR=2V Conditions 0.30 VR = 0.5 V to -1.0V f = 1 MHz Notes: 1. VF for diodes in pairs is 15.0 mV maximum at 1.0 mA. 2. CT for diodes in pairs is 0.05 pF maximum at -0.5V. RF Electrical Specifications, TC = +25C, Single Diode Part Number HSMS- Typical Tangential Sensitivity TSS (dBm) @ f = 915 MHz 2850 - 57 2852 2855 285B 285C 285L 285P Test Video Bandwidth = 2 MHz Conditions Zero Bias Typical Voltage Sensitivity g (mV/W) @ f = 915 MHz Typical Video Resistance RV (K) 40 8.0 Power in = -40 dBm RL = 100 K, Zero Bias Zero Bias Absolute Maximum Ratings, TC = +25C, Single Diode Symbol Parameter Unit PIV Peak Inverse Voltage V TJ Junction Temperature C 150 150 TSTG Storage Temperature C -65 to 150 -65 to 150 C -65 to 150 -65 to 150 C/W 500 150 TOP Operating Temperature jc Thermal Resistance[2] ESD WARNING: Handling Precautions Should Be Taken To Avoid Static Discharge. Absolute Maximum[1] SOT-23/143 SOT-323/363 2.0 2.0 Notes: 1. Operation in excess of any one of these conditions may result in permanent damage to the device. 2. TC = +25C, where TC is defined to be the temperature at the package pins where contact is made to the circuit board. Equivalent Linear Circuit Model Parameter HSMS-285x chip Rj RS Cj RS = series resistance (see Table of SPICE parameters) C j = junction capacitance (see Table of SPICE parameters) Rj = 8.33 X 10-5 nT Ib + Is where Ib = externally applied bias current in amps Is = saturation current (see table of SPICE parameters) T = temperature, K n = ideality factor (see table of SPICE parameters) Note: To effectively model the packaged HSMS-285x product, please refer to Application Note AN1124. SPICE Parameters Units BV V CJ0 pF EG eV I BV A IS A N RS PB (VJ) V PT (XTI) M HSMS-285x 3.8 0.18 0.69 3 E -4 3 E-6 1.06 25 0.35 2 0.5 Typical Parameters, Single Diode 10000 1000 1 0.1 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 VF - FORWARD VOLTAGE (V) Figure 1. Typical Forward Current vs. Forward Voltage. 3.1 OUTPUT VOLTAGE (mV) 2.9 2.7 FREQUENCY = 2.45 GHz PIN = -40 dBm RL = 100 K 2.5 2.3 2.1 1.9 1.7 1.5 1.3 MEASUREMENTS MADE USING A 1.1 FR4 MICROSTRIP CIRCUIT. 0.9 0 10 20 30 40 50 60 70 80 90 100 TEMPERATURE (C) Figure 4. Output Voltage vs. Temperature. 915 MHz VOLTAGE OUT (mV) 10 0.01 30 RL = 100 K VOLTAGE OUT (mV) IF - FORWARD CURRENT (mA) 100 100 10 1 0.1 -50 DIODES TESTED IN FIXED-TUNED FR4 MICROSTRIP CIRCUITS. -40 -30 -20 -10 0 POWER IN (dBm) Figure 2. +25C Output Voltage vs. Input Power at Zero Bias. RL = 100 K 10 915 MHz 1 0.3 -50 DIODES TESTED IN FIXED-TUNED FR4 MICROSTRIP CIRCUITS. -40 -30 POWER IN (dBm) Figure 3. +25C Expanded Output Voltage vs. Input Power. See Figure 2. -5 R j = 8.33 X 10 n T = RV- Rs +the I b Schottky Barrier The HeightIof S Applications Information Introduction Avago's HSMS285x family of Schottky detector diodes has been developed specifically for low cost, high volume designs in small signal (Pin < -20 dBm) applications at frequencies below 1.5 GHz. At higher frequencies, the DC biased HSMS-286x family should be considered. In large signal power or gain control applications (Pin >20 dBm), the HSMS-282x and HSMS-286x products should be used. The HSMS-285x zero bias diode is not designed for large signal designs. Schottky Barrier Diode Characteristics Stripped of its package, a Schottky barrier diode chip consists of a metal-semiconductor barrier formed by deposition of a metal layer on a semiconductor. The most common of several different types, the passivated diode, is shown in Figure 5, along with its equivalent circuit. RS METAL PASSIVATION N-TYPE OR P-TYPE EPI PASSIVATION LAYER SCHOTTKY JUNCTION Cj Rj N-TYPE OR P-TYPE SILICON SUBSTRATE CROSS-SECTION OF SCHOTTKY BARRIER DIODE CHIP EQUIVALENT CIRCUIT Figure 5. Schottky Diode Chip. RS is the parasitic series resistance of the diode, the sum of the bondwire and leadframe resistance, the resistance HSMS-285A/6A fig 9 of the bulk layer of silicon, etc. RF energy coupled into RS is lost as heat -- it does not contribute to the rectified output of the diode. CJ is parasitic junction capacitance of the diode, controlled by the thickness of the epitaxial layer and the diameter of the Schottky contact. Rj is the junction resistance of the diode, a function of the total current flowing through it. -5 R j = 8.33 X 10 n T = RV- Rs IS + Ib = 0.026 at 25C I S + Ib where V -(see IRS table of SPICE parameters) n = ideality factor I = IS (exp T = temperature in K - 1) 0.026 IS = saturation current (see table of SPICE parameters) Ib = externally applied bias current in amps RS = Rd - 0.026 IS is a function of diode If barrier height, and can range from picoamps for high barrier diodes to as much as 5 A for very low barrier diodes. RV 26,000 IS + Ib ( ) The current-voltage characteristic of a Schottky barrier 0.026 = at room temperature at 25C diode is described by the following I +I equation: S b I = IS (exp V - IR ( 0.026 ) - 1) S On a semi-log plot (as shown in the Avago catalog) the RS = graph Rd - 0.026 current will be a straight line with inverse slope If 2.3 X 0.026 = 0.060 volts per cycle (until the effect of RS is seen in a curve that droops at high current). All Schottky diode curves have the same slope, but not necessarRV 26,000 ily the same value IS + Ib 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 ntype 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 applications) are realized on ptype silicon. Such diodes suffer from higher values of RS than do the ntype. Thus, p-type diodes are generally reserved for small signal detector applications (where very high values of RV swamp out high RS) and n-type diodes are used for mixer applications (where high L.O. drive levels keep RV low). Measuring Diode Parameters The measurement of the five elements which make up the low frequency equivalent circuit for a packaged Schottky diode (see Figure 6) is a complex task. Various techniques are used for each element. The task begins with the elements of the diode chip itself. CP LP RV RS Cj FOR THE HSMS-285x SERIES CP = 0.08 pF LP = 2 nH Cj = 0.18 pF RS = 25 RV = 9 K Figure 6. Equivalent Circuit of a Schottky Diode. -5 R j = 8.33 X 10 n T = RV- Rs IS + Ib 0.026 = at 25C I S + Ib RS is perhaps the easiest to measure accurately. The V-I curve is measured for the diode under forward bias, and - IRScurve is taken at some relatively high the slope ofVthe I = IS (exp - 1)as 5 mA). This slope is converted value of current (such 0.026 into a resistance Rd. ( ) RS = Rd - 0.026 If RV and CJ are very difficult to measure. Consider the impedance26,000 of CJ = 0.16 pF when measured at 1 MHz -- it RV is approximately IS + Ib 1 M. For a well designed zero bias Schottky, RV is in the range of 5 to 25 K, and it shorts out the junction capacitance. Moving up to a higher frequency enables the measurement of the capacitance, but it then shorts out the video resistance. The best measurement technique is to mount the diode in series in a 50 microstrip test circuit and measure its insertion loss at low power levels (around -20 dBm) using an HP8753C network analyzer. The resulting display will appear as shown in Figure 7. Detector Circuits When DC bias is available, Schottky diode detector circuits can be used to create low cost RF and microwave receivers with a sensitivity of -55 dBm to -57 dBm.[1] These circuits can take a variety of forms, but in the most simple case they appear as shown in Figure 8. This is the basic detector circuit used with the HSMS285x family of diodes. In the design of such detector circuits, the starting point is the equivalent circuit of the diode, as shown in Figure 6. Of interest in the design of the video portion of the circuit is the diode's video impedance -- the other four elements of the equivalent circuit disappear at all reasonable video frequencies. In general, the lower the diode's video impedance, the better the design. RF IN Z-MATCH NETWORK VIDEO OUT -10 50 INSERTION LOSS (dB) -15 0.16 pF 50 -20 IS + Ib -25 0.026 I S + Ib at 25C Figure=8. Basic Detector Circuits. 50 9 K -30 50 -35 -40 Z-MATCH RF 8.33 X 10-5 n T = RVIDEO R j = NETWORK - Rs OUT IN V 3 10 100 1000 3000 FREQUENCY (MHz) Figure 7. Measuring C J and RV. At frequencies below 10 MHz, the video resistance domHSMS-285A/6A fig 10 inates the loss and can easily be calculated from it. At frequencies above 300 MHz, the junction capacitance sets the loss, which plots out as a straight line when frequency is plotted on a log scale. Again, calculation is straightforward. LP and CP are best measured on the HP8753C, with the diode terminating a 50 line on the input port. The resulting tabulation of S11 can be put into a microwave linear analysis program having the five element equivalent circuit with RV, CJ and RS fixed. The optimizer can then adjust the values of LP and CP until the calculated S11 matches the measured values. Note that extreme care must be taken to deembed the parasitics of the 50 test fixture. The situation is somewhat more complicated in the design of the V -RF IRS impedance matching network, which I = IS (exp the package - 1) inductance and capacitance includes 0.026 (which can be tuned out), the series resistance, the junction capacitance and the video resistance. Of these five elements of the diode's equivalent circuit, the four paraR = Rd - 0.026 sitics Sare constants If and the video resistance is a function of the current flowing through the diode. ( ) RV 26,000 IS + Ib where IS = diode saturation current in A Ib = bias current in A Saturation current is a function of the diode's design,[2] and it is a constant at a given temperature. For the HSMS-285x series, it is typically 3 to 5 A at 25C. Saturation current sets the detection sensitivity, video resistance and input RF impedance of the zero bias Schottky detector diode. Since no external bias is used with the HSMS-285x series, a single transfer curve at any given frequency is obtained, as shown in Figure 2. [1] Avago Application Note 923, Schottky Barrier Diode Video Detectors. The most difficult part of the design of a detector circuit is the input impedance matching network. For very broadband detectors, a shunt 60 resistor will give good input match, but at the expense of detection sensitivity. When maximum sensitivity is required over a narrow band of frequencies, a reactive matching network is optimum. Such networks can be realized in either lumped or distributed elements, depending upon frequency, size constraints and cost limitations, but certain general design principals exist for all types.[3] Design work begins with the RF impedance of the HSMS-285x series, which is given in Figure 9. FREQUENCY (GHz): 0.9-0.93 Figure 11. Input Impedance. The input match, expressed in terms of return loss, is HSMS-285A/6A fig 15 given in Figure 12. 2 0.2 0.6 5 0 1 3 4 5 6 Figure 9. RF Impedance of the HSMS285x Series at-40 dBm. 915 MHz Detector Circuit Figure 10 illustrates a simple impedance matching network for a 915 MHz detector. 65nH VIDEO OUT WIDTH = 0.050" LENGTH = 0.065" -5 -10 -15 -20 0.9 HSMS-285A/6A fig 13 RF INPUT RETURN LOSS (dB) 1 GHz 2 100 pF WIDTH = 0.015" LENGTH = 0.600" TRANSMISSION LINE DIMENSIONS ARE FOR MICROSTRIP ON 0.032" THICK FR-4. Figure 10. 915 MHz Matching Network for the HSMS-285x Series at Zero Bias. 0.915 0.93 FREQUENCY (GHz) Figure 12. Input Return Loss. As can be seen, the band HSMS-285A/6A fig 16over which a good match is achieved is more than adequate for 915 MHz RFID applications. Voltage Doublers To this point, we have restricted our discussion to single diode detectors. A glance at Figure 8, however, will lead to the suggestion that the two types of single diode detectors be combined into a two diode voltage doubler[4] (known also as a full wave rectifier). Such a detector is shown in Figure 13. A 65 nH inductor rotates the impedance of the diode to Z-MATCH a point on the Smith Chart HSMS-285A/6A fig 14 where a shunt inductor can RF IN NETWORK pull it up to the center. The short length of 0.065" wide microstrip line is used to mount the lead of the diode's SOT323 package. A shorted shunt stub of length