PFM19030 SPECIFICATION 1930-1990 MHz, 30W, 2-Stage Power Module Enhancement-Mode Lateral MOSFETs This versatile PCS module provides excellent linearity and efficiency in a low-cost surface mount package. The PFM19030 includes two stages of Package Type: Surface Mount amplification, along with internal sense FETs that are on the same silicon PN: PFM19030SM die as the RF devices. These thermally coupled sense FETs simplify the task of bias temperature compensation of the overall amplifier. The module includes RF input, interstage, and output matching elements. The source and load impedances required for optimum operation of the module are much higher (and simpler to realize) than for unmatched Si LDMOS transistors of similar performance. The surface mount package base is typically soldered to a conventional PCB pad with an array of via holes for grounding and thermal sinking of the module. Optimized internal construction supports low FET channel temperature for reliable operation. Package Type: Flange PN: PFM19030F • IS95 CDMA Performance 5 Watts Average Output Level 20% Power Added Efficiency –49 dBc ACPR • 28 dB Gain • 30 Watts Peak Output Power • Internal Sense FETs (for improved bias control) Module Schematic Diagram Module Substrate Gate 1 RF IN Lead Q1 Die Carrier Q2 Die Carrier Q1 Q2 Input Match Output Match S1 Sense S1 Gate 2 Sense S2 D1 Input Match Drain 2 RF OUT Output Match Lead S2 Lead Lead Lead Lead Note: Additionally, there are 250 KOhm resistors connected in shunt with all leads, to enhance ESD protection. Page 1 of 15 Specifications subject to change without notice. U.S. Patent No. 6,822,321 http://www.cree.com/ Rev. 2 PFM19030 Electrical Specification Parameter Min Limits Typ Units Max Comments 1 Operating Frequency 1930 - 1990 MHz 2 Gain 27.0 29.0 31.5 dB Note 1. 3 Gain Compression at Pout =30 Watts - 0.8 1.5 dB Pulsed CW compression measurement (12 µsec pulse, 120 µsec period, 10% duty cycle). - ± 0.2 ± 0.3 dB - ± 0.8 ± 1.5 ° - 3.1 3.7 nanosec -45 -49 - dBc 18 20.5 - % 42 - % 24 27 30 Volts Testing for conformance with RF specifications is at +27 V. -40 - +115 °C Testing for conformance with RF specification is at +25 °C. - -0.033 - dB/°C Bias quiescent currents held constant. - - 30 Watts CW VSWR 10:1, all phase angles. No degradation in output power before & after test. -60 - - dBc - 1.9 2.1 °C/W 4 5 6 7 8 9 10 11 12 Gain Flatness over any 30 MHz bandwidth Deviation from Linear Phase over any 30 MHz bandwidth Group Delay ACPR with IS95A CDMA Pave = 5 W Efficiency under IS-95 Protocol, Pave = 5 W Efficiency @ 30W CW Output DC Drain Supply Voltage Operating Temperature Range (base temperature) Gain Variation versus Temperature 13 Output Mismatch Stress 14 Stability 15 Theta jc (channel) 16 17 18 Quiescent Currents a) Q1 b) Q2 Sense FET Current/RF FET Current Ratio a) Stg 1 Sense b) Stg 2 Sense ESD Protection a) Human Body Model b) Machine Model Page 2 of 15 75 260 mA mA 3.0 1.7 % % Class 1 Class M3 Includes delay of test fixture (~0.6 nanosec.). Note 3. Refer to applications data for performance with other protocols. Note 3. 0<Pout<44.8 dBm CW, 3:1 VSWR Theta jc is for output device. Verified with IR scan. Note 2. These DC quiescent currents are typical of the levels that produce optimum linearity for CDMA protocol. Ratio of sense FET current, relative to RF FET current. Ratios are: Stg 1: 33:1; Stg 2: 58:1 Gates of sense & RF FETs are DC connected. Measured with no RF signal present. a) 2000V, 100 pF, 1500 Ohms b) 400V, 200 pF, zero Ohms Mil STD 883E, Method 3015 for Human Body Model and for Machine Model. Specifications subject to change without notice. US Patent No.6,822,321 http://www.cree.com/ Rev. 2 PFM19030 Electrical Specification (Continued) MAXIMUM RATINGS Rating 19 20 21 22 23 24 DC Drain Supply a) Drain-to-Source Voltage, (VGS=0), D1 & D2 & Track D1 & Track D2 b) Normal Operation (Class AB operation) DC Gate Supply a) Gate-to-source Voltage (VDS=0) Normal Operation (Class AB operation) RF Input Power Maximum Power Dissipation (T ≤ +85 °C) a) Derate above +85 °C base temperature. Maximum Channel Operating Temperature Storage Temperature Range Symbol Value Units VDS +50 Volts DC VD_SUPPLY +30 Volts DC VGS VG_SUPPLY PIN PTOTAL -0.5<VGS<+15 0<VGS<+6 +25 65 -0.7 Volts DC Volts DC dBm Watts Watts/°C TCH TSTG +200 -40 to +150 °C °C RECOMMENDED SOURCE AND LOAD IMPEDANCES Impedance Units Nominal Source Impedance for Optimum Operation 19 + j1.9 Ohms Nominal Load Impedance for Optimum Operation 21 + j6.3 Ohms Comments Matched for near-optimum linearity and gain flatness. Impedance is looking from the module input lead into the input matching circuit. Reference plane is 0.105 inches from the input end (case edge)of the module. Matched for near-optimum linearity under CDMA protocol. Impedance is from the module output lead looking into the output matching circuit. Reference plane is 0.105 inches from the output end (case edge) of the module. Specification Notes: 1) The module is mounted in a test fixture with external matching elements for all testing. Quiescent current bias conditions are those appropriate for minimum ACPR under CDMA protocol. Supply voltage for all tests is +27 volts DC. Testing is at +25 °C unless otherwise specified. 2) Theta jc is measured with a package mounting (base) temp of +85 °C, and with 10 Watts CW output. 3) Pout=5Watts average; IS-95A protocol: IS95 Forward Link PPS+ 9CH. ACPR conditions: a) 900 kHz offset, 30 kHz BW, b) 2.75 MHz offset, 1 MHz BW. 4) Sense FETs are scaled versions of the main RF FETs, formed from electrically isolated cells at end of the RF structure. Current scales according to periphery (threshold voltages offset is less than ±150 millivolts between adjacent devices). RF & Sense FET gates and sources are DC connected. Drains are DC isolated. Leads S1 & S2 are DC connected to drains of sense FETs 1 & 2. Sources are connected to package base. Sense FETs are electrically isolated from the RF signals. Page 3 of 15 Specifications subject to change without notice. U.S. Patent No. 6,822,321 http://www.cree.com/ Rev. 2 PFM19030 Typical Module Performance T=+25 °C, unless otherwise noted. Data is for module in a test fixture with external matching elements. See following page for test fixture details. 29 60% 30 28 50% 27 40% 26 30% 25 20% Gain (dB) Gain (dB) 31 29 28 Efficiency Gain & Efficiency vs. Output Power Pulsed Measurement, Vdc=+27V, F=1960 MHz Typical Small-Signal Gain vs. Frequency 27 26 1840 1870 1900 1930 1960 1990 2020 2050 24 2080 10% 30 Frequency (MHz) 32 34 36 38 40 42 44 46 Ouptput Power (dBm) Typical Output Power at 1 dB Gain Compression vs Freq. & Supply Voltage Input and Output Return Loss vs Frequency. 47 Output Power (dBm) 0 Return Loss (dB) -2 -4 OUTPUT -6 -8 -10 P1dB(+27V) 46 P1dB(+28V) 45 44 43 INPUT -12 P1dB(+26V) 1870 -14 1900 1930 1960 1990 1900 1930 1960 1990 Frequency (MHz) 2020 2050 2020 Frequency (MHz) Typical CW Gain vs Swept CW Output Power, with Various Quiescent Bias Conditions Typical S21 Phase Variation Versus Frequency (normalized about average insertion phase) 30 3 29 Bias for Best 2-Tone IMDs 28 1 Gain (dB) Phase (degrees) 2 0 -1 27 26 -2 G(75/250 mA) G(68/225 mA) 25 -3 G(60/200 mA) G(82/275 mA) 1930 1945 1960 1975 1990 Frequency (MHz) T i m t i m e e d d e l a y e l a y o o f f s e t f Page 4 of 15 t e s t = f i x 3 . 2 t u n a n r e ) . o s e c 24 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 CW Swept Output Power (dBm) ( i n c l u d e s Note: This data illustrates the significance of quiescent bias current level. The unit was press mounted in the fixture & thermal effects are exagerated for this CW test. Specifications subject to change without notice. U.S. Patent No. 6,822,321 http://www.cree.com/ Rev. 2 PFM19030 Typical Module Performance T=+25 °C, unless otherwise noted. Data is for module in a test fixture with external matching elements. See following page for test fixture details. -20 IM3L -20 ACPR(-900 KHz) 30 IM3U -25 ACPR(+900 KHz) 27 IM5L -30 ACPR(-1.25 MHz) 24 -35 ACPR(+1.25 MHz) 21 IM5U -30 IM7L ACPR (dBc) Intermodulation Distortion (dBc) -10 IM7U -40 -50 -60 -70 30 31 32 33 34 35 36 37 38 39 40 Average Output Power (dBm) 41 42 43 ACPR(-2.75 MHz) -40 12 -55 9 -60 6 -65 3 -70 0 F1=1959.5 MHz, F2=1960.5 MHz Vsupply = +27 V, Idsq1 = 75 mA, Idsq2=250 mA IM Rejection (dBc) IM Rejection (dBc) 32 33 34 35 36 37 38 Average CDMA Output Power (dBm) 39 -20 IM3L IM3U IM5L IM5U IM7L IM7U -20 31 2 IS95 CDMA Signal IM Distortion vs. Ave Output Power (F=1955, 1965 MHz) 2-Tone IMD Rejection vs. Tone Separation (Peak Envelope Power = 44.5 dBm) -10 15 -50 30 0 18 ACPR(+2.75 MHz) PAE (%) -45 Efficiency (%) Single-Signal IS95 CDMA ACPR & Efficiency vs Average Output Power (F=1960 MHz) Typical CW 2-Tone Intermods vs. Output Power -30 -40 -50 -25 IM3(+15 MHz) -30 IM3(-15 MHz) -35 IM5(-25 MHz) -40 IM5(+25 MHz) -45 -50 -55 -60 10 20 30 40 -60 50 30 CW Tone Separation (MHz) 31 32 33 34 35 36 CDMA Total Average Power (dBm) 37 38 WCDMA ACLR & Efficiency vs Output Power (F=1960 MHz, Test Model 1) F1=1930 MHz, F2=1930.5 MHz to 1980 MHz Vsupply = +27 V, Idsq1 = 75 mA, Idsq2=250 mA -15 28 -20 -25 ACLR (dBc) 24 ACLR(-5 MHz) 20 ACLR (+5 MHz) Efficiency -30 16 -35 12 -40 8 -45 4 -50 0 30 Page 5 of 15 Efficiency (%) 0 31 32 33 34 35 36 37 38 Average WCDMA Output Power (dBm) Specifications subject to change without notice. U.S. Patent No. 6,822,321 http://www.cree.com/ 39 Rev. 2 PFM19030 Typical Module Performance T=+25 °C, unless otherwise noted. Data is for module in a test fixture with external matching elements. See following page for test fixture details. EDGE EVM & Efficiency vs. Pout 2-Tone 3rd Order IMD Rejection vs. Pout & First Stage Quiescent Bias Currents 30.0% -20 10 25.0% 8 20.0% Efficiency 6 15.0% 4 10.0% EVM 2 5.0% IMD Rejection (dBc) RMS EVM % -25 Efficiency Efficiency Error Vector Magnitude (%) 12 IM3(75/250) IM3(82/250) -30 -35 -40 IM3(67/250) Idsq1=Opt-20% IM3(60/250) -10% -45 +10% -50 Idsq1=Optimum, 75 mA -55 0 -60 0.0% 26 28 30 32 34 36 38 40 Average Output Power (dBm) 42 44 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 Average Output Power (dBm) 2-Tone 3rd Order IMD Rejection vs. Pout & Second Stage Quiescent Bias Currents EDGE ACPR vs. Average Pout 0 ACPR (dBc) -20 lower 200khz -20 IM3(75/250) upper 200khz -25 IM3(75/275) -30 IM3(75/225) -35 IM3(75/200) IMD Rejection (dBc) -10 lower 250khz upper 250khz -30 lower 400khz -40 upper 400khz lower 600khz -50 upper 600khz -60 lower 1.2mhz +10% -45 -50 -10% Idsq2 = Optimum, 250 mA -55 upper 1.2mhz -70 Idsq2=Optimum -20% -40 -60 -80 36 37 Page 6 of 15 38 39 40 41 Average Output Power (dBm) 42 43 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 Average Output Power (dBm) Specifications subject to change without notice. U.S. Patent No. 6,822,321 http://www.cree.com/ Rev. 2 PFM19030 PFM19030SM Package Outline PFM19030F Package Outline Page 7 of 15 Specifications subject to change without notice. U.S. Patent No. 6,822,321 http://www.cree.com/ Rev. 2 PFM19030 Module Application Notes The PFM19030 was designed to provide a versatile low cost solution for a wide variety of wireless applications requiring 30 Watt peak output levels. This hybrid module contains two stages of Si LDMOS FET amplification: a nominally 5 Watt input stage driving a 30 Watt output stage. The module is optimized for efficient, linear operation with EDGE and CDMA signals. The input and output of this module are partially matched, and require source and load impedances of nominally 19 and 21 Ohms (much higher than typically required by unmatched Si LDMOS FETs). These source and load impedances can be achieved with compact conventional external PCB circuitry. Performance for particular signal protocols can be improved slightly by small adjustments in quiescent currents and load impedances presented to the module. The data presented in the previous pages was taken at one set of quiescent currents and in a fixture with source and load impedances that were fixed for all measurements. The data presented is generally representative of the performance – benefits from further optimization in quiescent current are small. In addition to the two RF gain stages, there are Sense FET (thermally tracking) devices that serve as optional DC circuit elements. The Sense FETs are fabricated on the same epi material with nominally identical physical characteristics (but smaller gate periphery) as the RF devices. The sense devices can be applied as temperature compensation elements in conjunction with external bias circuitry. Alternatively, the two-stage amplifier can be operated with the Sense FETs unused (S1 and S2 leads floating). The base of the module is high conductivity copper of 40 mil thickness. It is well matched to typical PCB material, and it serves as a heat spreader for the device when mounted as a surface-mount component. The module thermal characteristics were measured with the unit soldered to a 20 mil thick PCB material with an array of plated via holes for electrical grounding and thermal sinking. IR scans of this configuration demonstrated maximum die channel temperatures of 142 degrees C with a PCB base temperature of +95 degrees C, and 10 Watts CW output power. These modules can be provided in tape-and-reel configuration for high volume applications. Typical PCB Mounting Pattern The module outline is indicated by dashed line (0.60 X 1.00 inches). The ground pad is 1.030 X 0.630 inches. Ground vias in this example are 28 mil diameter on 35 mil (or 70 mil) centers. Thermal resistance is proportional to the thickness of the PC board (height of vias), and inversely proportional to the total ground hole array periphery (and thickness of plating in the holes). The densely spaced vias in this layout (on 35 mil spaces) are located in areas of maximum heat generation. The gap between the lead pads and the ground pad is 25 mils. Note that the underside of the PCB must be connected to a thermal heat sink and ground. The above hole pattern is an example of one that maximizes thermal transfer. There are numerous alternative approaches. Depending on the application (signal protocol, thermal environment, etc.), the number of via holes can be reduced. High average power applications require the most extensive thermal sinking. Page 8 of 15 Specifications subject to change without notice. U.S. Patent No. 6,822,321 http://www.cree.com/ Rev. 2 PFM19030 Recommended Passive Bias Circuit This schematic demonstrates a method of applying the Sense FETs internal to the module that uses passive external circuitry. The circuit maintains a constant current through the Sense FETS, independent of temperature of the die. The Sense FETs are configured in this case as diodes. The temperature dependence of the Vf of the diode is very similar to that of the RF FET gate voltage, and therefore the quiescent current remains nearly constant over a wide temperature range. The advantage of this circuit is its simplicity and stability (avoidance of operational amplifiers) under all layout conditions. The main limitation of the circuit is that quiescent currents must be adjusted for each individual module (they are not easily pre-set with precision). GND J1 8 7 +10 to +20 V Gate +27 V 6 5 4 3 2 Note: Typical Q1 diode bias = 1.4 mA (VG1 ~ 3.96V) Typical Q2 diode bias = 2.7 mA (VG2 ~ 4.21V) (based on 6/4/04 measurements) 1 C29 C28 S1 C27 S2 C12 C11 C10 R6 C24 C23 C22 C21 C20 C19 R5 R2 C9 C18 C17 C16 C15 C8 Drain 1 C2 RF OUT RF Out C1 C7 Sense D2 Gate 2 PFM19030 R3 R1 Sense D1 RF IN C4 C3 Page 9 of 15 C6 RF Input C5 Specifications subject to change without notice. U.S. Patent No. 6,822,321 http://www.cree.com/ Rev. 2 PFM19030 Passive Bias Circuit Parts List Designator C2 C3 C5 C4 C6 C1, C7, C19, C20 C10, C13, C14, C15, C8, C11, C16, C21 C22 C23, C9, C17, C12 C24, C18 R5 R6 R1 R3 C27 C29 C28 S1, S2 Page 10 of 15 Description Qty CAP, 1.2 PF±0.1 pF, 0603, ATC 600S CAP, 2.0 PF±0.1 pF, 0603, ATC 600S CAP, 1.8 PF±0.1 pF, 0603, ATC 600S CAP, 4.7 PF±0.1 pF, 0603, ATC 600S CAP, 3.0 PF±0.1 pF, 0603, ATC 600S CAP, 27 PF±5%, 0603, ATC 600S CAP, 27 PF±5%, 100V (min), 0603, any vendor. CAP, 470 PF ±10%,100 V, 0603, any vendor. CAP, 3300 PF±10%, 100 V, 0603, Murata GRM39X7R332K100??, or equivalent. CAP, 15000 PF±10%, 100 V, 0805, MurataGRM40X7R153K100??, or equivalent. CAP, 150000 1206, 50V, X7R, 10% Suggest Murata GRM42-6-X7R-154-K-050-A-L or equivalent. RES, potentiometer, 10Kohms, Digikey SM4W103-ND RES, potentiometer, 5 Kohms, Digikey SM4W502-ND RES, 1/16W, 0603, 1000 ohms, 5% RES, 1/16W, 0805, 124 Ohms, 5% CAP, 2.2uf SMT TANTALUM, 50V (240097) CAP, 10uf 16V SMT TANTALUM (240096) CAP, 47UF, 50V, ELECTR SMT (240087) SPST Switch, Digikey PN CKN1100CT-ND 1 1 1 1 1 4 4 4 1 Specifications subject to change without notice. U.S. Patent No. 6,822,321 http://www.cree.com/ 4 2 1 1 1 1 1 1 1 2 Rev. 2 PFM19030 Test Fixture A metal-backed PCB with clamps for securing the module is used for module electrical testing and for product demonstration. The fixture is supplied mounted to a finned heat sink. The fixture schematic is provided on the following page. This test fixture uses an active bias circuit, which sets the bias circuit through the Sense FETs (configured as FETs) and applies the derived gate voltage to the associated RF FETs. This assures particular quiescent bias currents, with accuracy determined by the Sense FET-to-RF FET current ratios. Page 11 of 15 Specifications subject to change without notice. U.S. Patent No. 6,822,321 http://www.cree.com/ Rev. 2 PFM19030 Test Fixture Schematic +27 V OpAmp +27 V GND J2 Not Used for Demo Fixture J1 8 7 6 5 4 3 2 J2 1 8 7 6 5 4 3 2 1 RZ_FS1 RZ_FS2 C37 C31 C34 C36 R12 C32 R11 R32 R31 R16 R13 R14 C40 C33 5 U1 4 LM8261 1 + 3 2 R19 R36 R33 C42 R34 C41 R37 R20 R15 U2 5 LM8261 + 3 2 C35 C43 R39 R35 R40 S2 D2 R38 R17 R18 4 S1 D1 C28 C27 C26 C12 C11 C10 C25 C24 C23 C22 C21 C20 C19 C14 C9 C18 C17 C16 C15 C8 Drain 1 C2 RF OUT RF Out C1 C7 Sense D2 Gate 2 PFM19030SM R2 R1 Sense D1 RF IN C4 C3 C6 RF Input C5 See the following pages for the parts list and a description of the principle of operation. Note that an alternative, less complex bias scheme is provided later in this applications note. The advantage of the above bias design is that bias currents are set by the RF-to-Sense FET ratios, and once the optimum bias circuit resistor (potentiometer) values are established, the circuit can stay fixed for multiple modules (thus eliminating module-specific bias alignment). Additionally, aging effects are minimized because of the Page 12 of 15 Specifications subject to change without notice. U.S. Patent No. 6,822,321 http://www.cree.com/ Rev. 2 PFM19030 similar bias conditions for Sense and RF FETs. The disadvantage of this design is its relative complexity and the incorporation of operational amplifiers, for which stability is potentially circuit layout dependent. Parts List for Cree Microwave Test Fixture Designator C2 C3 C5 C4 C6 C1, C7, C19, C20 C10, C13, C14, C15, C8, C11, C16, C21 C22 C9, C23, C17, C12 C18, C24, C25, C26, C31, C34 C27, C37 C28 C33, C35 C32, C36 C40, C41, C42, C43 R1 R2 R11, R12 R31, R32 R13, R14, R33, R34 R16, R15, R35, R36 R19, R39 R18 R38 R20, R40 R17, R37 RZ_FS1, RZ_FS2 D1, D2 S1, S2 U1, U2 Description CAP, 1.2 PF±0.1 pF, 0603, ATC 600S CAP, 2.0 PF±0.1 pF, 0603, ATC 600S CAP, 1.8 PF±0.1 pF, 0603, ATC 600S CAP, 4.7 PF±0.1 pF, 0603, ATC 600S CAP, 3.0 PF±0.1 pF, 0603, ATC 600S CAP, 27 PF±5%, 0603, ATC 600S CAP, 27 PF±5%, 100V (min), 0603, any vendor. CAP, 470 PF ±10%,100 V, 0603, any vendor. CAP, 3300 PF±10%, 100 V, 0603, Murata GRM39X7R332K100 CAP, 15000 PF±10%, 100 V, 0805, MurataGRM40X7R153K100 CAP, 150000 1206, 50V, X7R, 10% Murata GRM42-6-X7R-154-K-050-A-L CAP, 2.2uf SMT TANTALUM, 50V CAP, 47UF, 50V, ELECTR SMT CAP, 18,000 PF ±10%,100 V, 0603 CAP, 33,000 PF ±10%,100 V, 0603 CAP, 1000 PF ±10%,100 V, 0603. RES, 1/16W, 0603, 1000 ohms, 5% RES, 1/16W, 0805, 124 Ohms, 5% RES, 1/16W, 0603, 332 Ohms, 1% RES, 1/16W, 0603, 147 Ohms, 1% RES, 1/16W, 0603, 2370 Ohms, 1% RES, 1/16W, 0603, 511 KOhms, 1% RES, 1/16W, 0603, 100 KOhms, 5% RES, 1/16W, 0603, 3320 Ohms, 5% RES, 1/16W, 0603, 2000 Ohms, 5% RES, 1/8W, 1206, 1000 Ohms, 5% RES, potentiometer, 10 Kohms, Digikey SM4W103-ND, 11T RES, 1/16W, 0805, 0 Ohms (used as jumpers, demo fixture only) Zener diode, 6.2 V, Digikey PN BZT52C6V27DICT-ND SPST Switch, Digikey PN CKN1100CT-ND Op Amp, High Output, LM8261M5 (5 pin, SOT23 package) Qty 1 1 1 1 1 4 4 4 1 4 6 2 1 2 2 4 1 1 2 2 4 4 2 1 1 2 2 2 2 2 2 It is also possible to bias the two stages in a conventional manner, with the two tracking FET drains left unused (floating or grounded). The above bias circuits are just two of several possibilities. Page 13 of 15 Specifications subject to change without notice. U.S. Patent No. 6,822,321 http://www.cree.com/ Rev. 2 PFM19030 Test Fixture Active Bias Circuit Principles of Operation The test fixture operates off of a single voltage supply. It contains two switches and two potentiometers. The switches provide for independent on/off for the input and output devices of the module. The potentiometers allow adjustment of quiescent current level of each stage. The adjustments should be made with no RF applied to the module. Q1 Die Carrier Q1 Output Match Input Match Vsupply S1 Vsupply R1 <<Rbias R1 R1 - Differental Amp + Ids_sense Ireference Rbias Principal of Operation of Bias Circuitry The principal of operation of the fixture bias circuit is demonstrated in the above Figure. The potentiometer establishes a reference current, and the operational amplifier adjusts gate voltage to maintain that current in the sense device. The same DC gate voltage is also applied to the main (RF) device. Sense devices are scaled versions of the main (RF) devices, on the same die (to facilitate temperature tracking). As the temperature of the die changes due to RF drive (or ambient temperature changes), the operational amplifier maintains constant current through the Sense FET, and thus constant quiescent bias for the main (RF) FET. No RF signal is applied to the Sense FET. There is a separate independent bias circuit for the input (Q1) device and for the output device (Q2) of the module. Experience has shown this bias circuit to be a reliable method of maintaining tight control of quiescent current over operating temperature, and for minimizing the impact of device aging effects on amplifier performance. However, there are some precautions regarding use of this circuit. The principle of the circuit is for the differential amplifier (op amp) to adjust gate voltage until the desired current is achieved through the sense FETs. If the current path is interrupted (thereby not allowing Ids_sense to flow), the operational amplifier will increase gate bias in an attempt to increase current, with the possibility that the quiescent bias current in the RF FET may increase beyond a safe limit (the device may be destroyed). The zener diodes in the test fixture circuit (D1 and D2, test fixture schematic) are safeguards for prohibiting excessive gate voltage to be applied to the transistors. Page 14 of 15 Specifications subject to change without notice. U.S. Patent No. 6,822,321 http://www.cree.com/ Rev. 2 PFM19030 Disclaimer: Specifications are subject to change without notice. Cree Microwave, Inc. believes the information contained within this data sheet to be accurate and reliable. However, no responsibility is assumed by Cree Microwave for any infringement of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Cree Microwave. Cree Microwave makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose. “Typical” parameters are the average values expected by Cree Microwave in large quantities and are provided for information purposes only. These values can and do vary in different applications, and actual performance can vary over time. All operating parameters should be validated by customer’s technical experts for each application. Cree Microwave products are not designed, intended, or authorized for use as components in applications intended for surgical implant into the body or to support or sustain life, in applications in which the failure of the Cree product could result in personal injury or death, or in applications for planning, construction, maintenance or direct operation of a nuclear facility. Cree Microwave is a trademark and Cree and the Cree logo are registered trademarks of Cree, Inc. Contact Information: Cree Microwave, Inc. 160 Gibraltar Court Sunnyvale, CA 94089-1319 Sheryle Henson (Cree Microwave—Marketing Manager) 408-962-7783 Tom Dekker (Cree Microwave—Sales Director) 919-313-5639 Page 15 of 15 Specifications subject to change without notice. U.S. Patent No. 6,822,321 http://www.cree.com/ Rev. 2