Limiter Diodes CLA Series Features Low Loss 4 kW Coarse Limiters 210 4 240 200 Watt Midrange Limiters 10 mW Clean-Up Limiters Description Chip Dimensions Alpha has pioneered the microwave limiter diode. Because all phases of manufacturing, from design through epitaxy to the finished device, are specifically tailored to this application, Alpha limiters have lower loss, greater bandwidth and faster turn-on time than equivalent competitive diodes. Alpha's series of thin base limiter diodes will provide passive receiver protection over the entire range of frequencies from 100 MHz to beyond 30 GHz. These diodes are PIN silicon devices with a thin intrinsic region, typically 2 microns for the CLA4603 and 4601, 4 microns for the CLA4606, 4604, and 4605, and 15 microns for the CLA4607 and 4608 series. They operate as a power dependent variable resistance, through mechanisms of charge injection and storage, similar to rectification, when used in microwave circuitry as shown in Figure 1. The different "I" region thicknesses and capacitances provide variable threshold and leakage power levels and power handling capability. The CLA4607 and 4608, which can handle incident pulses of up to 4 kW for 1 ms, are used as "coarse" prelimiters, with the thinner diodes used as clean-up or "fine" limiters to reduce the leakage power to as low as 10 mW for protecting the most sensitive receivers. Alpha Industries * * Fax Model Number N b DOT Diameter (Typ.) Chip Style St l Inches mm CLA4601-000 CLA4602-000 0.0012 0.0015 0.02 0.04 150-806 150-806 CLA4603-000 0.0015 0.04 149-801 CLA4604-000 0.0015 0.04 150-806 CLA4605-000 0.0025 0.06 150-801 CLA4606-000 0.002 0.05 149-801 CLA4607-000 CLA4608-000 0.003 0.005 0.75 0.12 149-801 149-801 * E-mail * Visit our web site: 4-11 Limiter Diodes CLA Series CLA4607 RF CLA4606 CLA4603 Ground Return < 1 Receiver Figure 1. Cascaded Limiter Design 0.020" Typ. Ground Plane CLA4607 RR 50 Ohm Connector EEE EE EE E EEE E EEE E EEE E EE EEE EE E EEE E EEE E EEE E ECCCCCCCCCCCCC EE ECCCCCCCCCCCCC EE 0.001" Gold Wire Bond Typ. Solder or Epoxy Die Bond Microstrip Board TFG 0.006" Thick Typ. Schottky Barrier CMB7602 RF Figure 3. Side View Receiver Figure 2. Quasi-Active Limiter The CLA4603 and 4606 limiter diodes are constructed in a passivated flat-chip configuration and are available in a basic chip form or encapsulated in a variety of Alpha glass or ceramic packages, a few of which are shown. Limiter diodes with lower capacitance values, to 0.08 pF, constructed with a passivated mesa configuration, are available in the CLA4601 and 4605 series. The mesa devices offer low CJ, and therefore broader bandwidth, lower loss, and faster response, at reduced power. These diodes are also available in chip package form, and represent the ultimate in limiter performance, not approached by other manufacturers. The CLA4607 diodes (highest power) are available in both planar and mesa construction. Figures 3 and 4 illustrate the fundamental structures of diodes mounted in a 50 ohm microstrip circuit. The diode characteristics listed in the table refer to chips mounted in such a circuit. The designer can use these parameters in modeling the chip in any package, provided overall package parasitics are considered. Additional bonding and handling methods are contained in Alpha application notes. 4-12 Alpha Industries * * Fax Diode Typ. TFG Board EEEEEEEEEEEEEE EEEEEEEEEEEEEE EEEEEEEEEEEEEE EEEEEEEEEEEEEE EEEEEEEEEEEEEE EEEEEEEEEEEEEE Ground Return 2 1 50 Ohm Conductor 0.022" Typ Figure 4. Top View Coil for Ground Return 1 50 CJ RR 2 CJ RP CJ 50 RP Figure 5. Low Level Equivalent Circuit * E-mail * Visit our web site: Limiter Diodes CLA Series Basic Application When the Schottky diode is directly coupled to the transmission line, in cascade after the coarse limiter, the leakage power will be less than if a zero ohm ground return were used. If the Schottky is decoupled too much, the leakage power increases, owing to the Alpha Industries * * Fax Coil for Ground Return 1 50 2 RS RS RS 50 Figure 6. High Power Equivalent Circuit 4 1.75 Bonding Wires Diode 50 Chip 50 0.50 pF 1.50 Single single Section Low Pass Filter 0.30 pF VSWR During the rise time of the incident pulse, the diodes behave in the following manner. The CLA4603, due to its thin "I" region, is the first to change to a low impedance. Experiments indicate that the CLA4603 reaches the 10 dB isolation point in about 1 ns and 20 dB in 1.5 ns with an incident power of 10 watts. The CLA4606 takes about 4 ns and the CLA4607 about 50 ns. Consequently, the CLA4603 provides protection during the initial stages of pulse rise time, with the thicker diodes progressively "turning on" as the power increases. With proper spacing (L1 and L2), the "on" diodes reflect high impedances to the upstream diodes, reducing the turn-on time for those diodes and ensuring that essentially all of the incident power is reflected by the input diode, preventing burnout of the thinner diodes. At the end of the pulse the process reverses, and the diodes "recover" to the high impedance state; the free charge which was injected in the "I" region by the incident power leaks off through the ground return and additionally is reduced by internal combination. With a ground return, recovery time is on the order of 50 ns. With a high impedance return, for example the circuit of Figure 2, the Schottky diodes recovers or 1 "opens" in practically zero time, and internal recombination, on the order of several diode lifetimes, is the only available mechanism for recovery. This recovery time can be long-on the order of 1 S for the CLA4607 series. The shunt resistor Rr minimizes the problem. One hundred ohms will approximately double the recovery time, compared to a short circuit. high DC impedance of a Schottky. Similarly, a 3.0 ohm ground return causes an increase of about 3 dB in leakage power compared to a zero ohm return. 1.25 0.15 pF 1.0 2 4 6 8 10 12 Frequency (GHz) 14 16 18 Figure 7. Typical VSWR for Low Pass Filters 0.5 Bonding Wires 50 Insertion Loss (dB) When designing microstrip limiters the bonding wire length and diameter, in conjunction with the chip capacitance, form a low pass filter (see Figure 7). Line lengths of (L1, and L2) are varied to provide broadband matching and flat leakage characteristics. Typically, L1 and L2 are on the order of 0.1 wavelength. In Figure 1, the CLA4607 chip provides about 20 dB attenuation, reducing a 1 kW input to 10 watts. The CLA4606 reduces this to 100 mW and the CLA4603 to about 20 mW. CJ Diode Chip RP 50 0.4 Single Diode Section 0.50 pF 0.30 pF 0.3 0.15 pF 0.2 0.1 2 4 6 8 10 12 14 16 18 Frequency (GHz) Figure 8. Typical Diode Insertion Loss vs. Frequency * E-mail * Visit our web site: 4-13 Limiter Diodes 100.0 Leakage Power Above 1.0 GHz (dB) Peak Normalized to Tabulated Value at 1.0 S ( C/W) CLA Series C/W CLA4607, 08 Series 10.0 C/W CLA4601, 02, 03, 04, 05, 06 Series 1.0 105 104 102 Diode Chip 50 50 +9 +6 +3 0 CW 2 4 6 8 10 12 14 16 18 Frequency (GHz) Pulse Length (Sec) Figure 9. Pulsed Thermal Impedance Figure 11. Leakage Power vs. Frequency +50 Diode Chip 50 1.0 +40 CLA4607 +30 Power Derating Factor Peak Power Output (dBm) 50 CLA4606 CLA4604 CLA4603 +20 CLA4601 +10 0 0 +10 +20 +30 +40 +50 +60 +66 0.75 0.50 0.25 -50C 0C +50C +100C +150C Case Temperature (C) Peak Pout Input (dBm) Figure 10. Typical Peak Leakage Power at 1 GHz Figure 12. Power Handling Capability vs. Temperature Ordering Information The table on the following page shows the part numbers for chip limiter diodes. Packaged limiter diodes may be specified by adding the package number to the chip number. For example, CLA4605-210 is the CLA4605-000 in the 210 package. 210 4-14 Alpha Industries * The recommended packages for limiter diodes are shown on page 6-11. Available through distribution: CLA4603-210 CLA4606-210 CLA4607-210 CLA4603-240 CLA4606-240 CLA4607-240 240 * Fax * E-mail * Visit our web site: Limiter Diodes CLA Series Electrical Specifications at 25C Part Number CLA4601-000 CLA4602-000 CLA4603-000 CLA4604-000 CLA4605-000 VB (V) CJ @ 0V (pF) CJ @ 6V (pF) Typ. Typ. Max. @10 mA () 0.12 0.10 0.20 0.20 15-30 20-45 30-60 RP 2 () P3 (C/W) @1.0 mA () Typ. Typ. 2.0 4.0 3000 15 0.15 1.5 3.0 2000 0.15 1.5 5.0 2000 0.12 0.10 2.0 4.0 0.20 0.15 1.5 4.0 RS Typical1 TL (ns) CW ((C/W)) Typ. 120 5 10 80 5 10 100 5 3000 10 100 7 2000 7 70 7 CLA4606-000 45-75 0.20 0.15 1.5 4.0 2000 7 80 10 CLA4607-000 120-180 0.20 0.15 1.5 3.5 2000 1.2 40 50 0.5 3.0 1000 0.3 15 100 @ 50V CLA4608-000 120-180 0.80 0.50 4 @ 50V Available through distribution. Typical Performance Peak Pin (1.0 S) (dBm) Threshold4 (dBm) Leakage4 POUT (dBm) Insertion Loss2 (dBm) CW5 Power In (W) Recovery6 Time, (ns) Max. Typ. Typ. Typ. Max. Typ. CLA4601-000 +47 +7 +21 0.1 2 5 CLA4602-000 +50 +7 +24 0.1 3 5 CLA4603-000 +50 +10 +22 0.1 2 10 CLA4604-000 +47 +12 +24 0.1 3 10 CLA4605-000 +50 +12 +27 0.1 4 10 CLA4606-000 +53 +15 +27 0.1 3 20 CLA4607-000 +60 +20 +39 0.1 6 50 CLA4608-000 +66 +20 +44 0.2 15 100 Part Number 1. Series resistance is measured at 100 MHz. 2. Chip loss can be represented as a resistance in shunt with the junction capacitance. RP is measured at 3 GHz, zero bias. Figure 9 indicates typical variation with frequency. Loss data shown are for 10 GHz for 0.15 and 0.30 pF chips, 5 GHz for 0.50 pF chips. Reflective loss is shown in Figure 8 and is included. Loss is measured at -10 dBm input. 3. Pulsed thermal impedance is given for a 1 S pulse. Figure 10 shows typical variation for longer pulse lengths. CW thermal impedance presumes infinite heat sink. 4. Threshold input power produces 1 dB increase in insertion loss. Figure 11 shows typical leakage power curves. Data taken for 1.0 GHz. Figure 12 shows typical variation with frequency. Note especially the roll-off of CLA4607 at higher frequency. 5. Note that CW power and average power are not synonymous. Power ratings are computed in terms of a peak junction temperature of 200C, for short pulses, an average junction temperature of 125C, and an ambient of 25C. Duty factor 0.001 assumed for maximum pulse power input. Figure 13 shows power derating with temperature. 6. Recovery time is measured with ground return (less than 1.0 ohm) to 1 dB excess loss, at 1 GHz. Outline Dimensions 149-801 150 Series Chip Style Bonding Pad Nominal (In.) 150-801 150-806 .002 (min) .0011 (min) METALIZED GOLD DOT Chip Size (In.) Min. Max. .010 .010 .014 .014 SILICON .004 - .006 METALIZED BACK CONTACT GOLD Alpha Industries * * Fax * E-mail * Visit our web site: 4-15