19-1248; Rev 1; 5/98 KIT ATION EVALU E L B AVAILA 10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs ____________________________Features ♦ Low-Phase-Noise Oscillator: -110dBc/Hz (25kHz offset from carrier) Attainable ________________________Applications _______________Ordering Information ♦ Operates from Single +2.7V to +5.25V Supply ♦ Low-Cost Silicon Bipolar Design ♦ Two Output Buffers Provide Load Isolation ♦ Insensitive to Supply Variations ♦ Low, 27mW Power Consumption (VCC = 3.0V) ♦ Low-Current Shutdown Mode: 0.1µA (typ) Analog Cellular Phones Digital Cellular Phones MAX2620EUA PART TEMP. RANGE -40°C to +85°C PIN-PACKAGE 8 µMAX 900MHz Cordless Phones MAX2620E/D -40°C to +85°C Dice* *Dice are tested at TA = +25°C, DC parameters only. 900MHz ISM-Band Applications Land Mobile Radio Pin Configuration appears at end of data sheet. Narrowband PCS (NPCS) ____________________________________________________Typical Operating Circuit VCC VCC 10Ω 1000pF 10nH 1000pF 1.5pF OUT 8 1 VCC1 C17 1.5pF C5 1.5pF 2 TANK VTUNE C3 2.7pF 1k D1 ALPHA SMV1204-34 CERAMIC RESONATOR L1 OUT TO MIXER MAX2620 VCC2 7 3 FDBK GND C6 C4 1pF 4 SHDN VCC BIAS SUPPLY 6 0.1µF 1000pF OUT 5 OUT TO SYNTHESIZER 51Ω SHDN VCC 1000pF 900MHz BAND OSCILLATOR ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 408-737-7600 ext. 3468. MAX2620 _________________General Description The MAX2620 combines a low-noise oscillator with two output buffers in a low-cost, plastic surface-mount, ultra-small µMAX package. This device integrates functions typically achieved with discrete components. The oscillator exhibits low phase noise when properly mated with an external varactor-tuned resonant tank circuit. Two buffered outputs are provided for driving mixers or prescalers. The buffers provide load isolation to the oscillator and prevent frequency pulling due to load-impedance changes. Power consumption is typically just 27mW in operating mode (VCC = 3.0V), and drops to less than 0.3µW in standby mode. The MAX2620 operates from a single +2.7V to +5.25V supply. MAX2620 10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs ABSOLUTE MAXIMUM RATINGS VCC1, VCC2 to GND................................................-0.3V to +6V TANK, SHDN to GND .................................-0.3V to (VCC + 0.3V) OUT, OUT to GND...........................(VCC - 0.6V) to (VCC + 0.3V) FDBK to GND ..................................(VCC - 2.0V) to (VCC + 0.3V) Continuous Power Dissipation (TA = +70°C) µMAX (derate 5.7mW/°C above +70°C) .....................457mW Operating Temperature Range MAX2620EUA .................................................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +165°C Lead Temperature (soldering, 10sec) .............................+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. DC ELECTRICAL CHARACTERISTICS (VCC1, VCC2 = +2.7V to +5.25V, FDBK = open, TANK = open, OUT and OUT connected to VCC through 50Ω, SHDN = 2V, TA = -40°C to +85°C, unless otherwise noted. Typical values measured at VCC1 = VCC2 = 3.0V, TA = +25°C.) (Note 1) PARAMETER CONDITIONS MIN Supply Current Shutdown Current SHDN = 0.6V Shutdown Input Voltage High TYP MAX UNITS 9.0 12.5 mA 0.1 2 µA 2.0 V Shutdown Input Voltage Low Shutdown Bias Current High SHDN = 2.0V Shutdown Bias Current Low SHDN = 0.6V 5.5 0.6 V 20 µA 0.5 µA Note 1: Specifications are production tested and guaranteed at TA = +25°C and TA = +85°C. Specifications are guaranteed by design and characterization at TA = -40°C. AC ELECTRICAL CHARACTERISTICS (Per Test Circuit of Figure 1, VCC = +3.0V, SHDN = VCC, ZLOAD = ZSOURCE = 50Ω, PIN = -20dBm (50Ω), fTEST = 900MHz, TA = +25°C, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP 10 MAX UNITS 1050 MHz Frequency Range TA = -40°C to +85°C (Note 2) Reverse Isolation OUT or OUT to TANK; OUT, OUT driven at P = -20dBm 50 dB Output Isolation OUT to OUT 33 dB Note 2: Guaranteed by design and characterization at 10MHz, 650MHz, 900MHz, and 1050MHz. Over this frequency range, the magnitude of the negative real impedance measured at TANK is greater than one-tenth the magnitude of the reactive impedances at TANK. This implies proper oscillator start-up when using an external resonator tank circuit with Q > 10. C3 and C4 must be tuned for operation at the desired frequency. 2 _______________________________________________________________________________________ 10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs (Per Typical Operating Circuit, VCC = +3.0V, VTUNE = 1.5V, SHDN = VCC, load at OUT = 50Ω, load at OUT = 50Ω, L1 = coaxial ceramic resonator: Trans-Tech SR8800LPQ1357BY, C6 = 1pF, TA = +25°C, unless otherwise noted.) PARAMETER Tuning Range Phase Noise Output Power (single-ended) Noise Power CONDITIONS MIN TYP VTUNE = 0.5V to 3.0V ±13 SSB @ ∆f = 25kHz -110 SSB @ ∆f = 300kHz -132 At OUT (Note 2) -6 -2 At OUT, per test circuit of Figure 1; TA = -40°C to +85°C (Note 3) -11 -8 At OUT (Note 3) -16 -12.5 fO ± >10MHz MAX UNITS MHz dBc/Hz dBm -147 dBm/Hz Average Tuning Gain 11 MHz/V Second-Harmonic Output -29 dBc Load Pull VSWR = 1.75:1, all phases 163 kHzp-p Supply Pushing VCC stepped from 3V to 4V 71 kHz/V Note 3: Guaranteed by design and characterization. TYPICAL OPERATING CIRCUIT PERFORMANCE—900MHz Band Inductor-Based Tank (Per Typical Operating Circuit, VCC = +3.0V, VTUNE = 1.5V, SHDN = VCC, load at OUT = 50Ω, load at OUT = 50Ω, L1 = 5nH (Coilcraft A02T), C6 = 1.5pF, TA = +25°C, unless otherwise noted.) PARAMETER Tuning Range Phase Noise Output Power (single-ended) Noise Power CONDITIONS MIN TYP VTUNE = 0.5V to 3.0V ±15 SSB @ ∆f = 25kHz -107 SSB @ ∆f = 300kHz -127 At OUT (Note 2) -6 -2 At OUT, per test circuit of Figure 1; TA = -40°C to +85°C (Note 3) -11 -8 At OUT (Note 3) -16 -12.5 fO ± >10MHz MAX UNITS MHz dBc/Hz dBm -147 dBm/Hz Average Tuning Gain 13 MHz/V Second-Harmonic Output -29 dBc Load Pull VSWR = 1.75:1, all phase angles 340 kHzp-p Supply Pushing VCC stepped from 3V to 4V 150 kHz/V Note 3: Guaranteed by design and characterization. _______________________________________________________________________________________ 3 MAX2620 TYPICAL OPERATING CIRCUIT PERFORMANCE—900MHz Band CeramicResonator-Based Tank __________________________________________Typical Operating Characteristics (Per test circuit of Figure 1, VCC = +3.0V, SHDN = VCC, ZLOAD = ZSOURCE = 50Ω, PIN = -20dBm/50Ω, fTEST = 900MHz, TA = +25°C, unless otherwise noted.) OUT OUTPUT POWER vs. FREQUENCY OVER VCC AND TEMPERATURE OUT OUTPUT POWER vs. FREQUENCY OVER VCC AND TEMPERATURE MAX2620-01 -5 C VCC = 5.25V -6 VCC = 5.25V -7 VCC = 5.25V TA = +85°C TA = +25°C TA = -40°C A TA = +85°C -11.5 TA = +25°C VCC = 2.7V -8 MAX2620-02 -11.0 POWER (dBm) POWER (dBm) MAX2620 10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs -12.0 TA = -40°C -12.5 VCC = 2.7V B -13.0 VCC = 2.7V -9 -13.5 0 200 400 600 800 1000 1200 0 FREQUENCY (MHz) 200 400 600 800 1000 1200 FREQUENCY (MHz) A: 10MHz BAND CIRCUIT B: NOT CHARACTERIZED FOR THIS FREQUENCY BAND. EXPECTED PERFORMANCE SHOWN. C: 900MHz BAND CIRCUIT Table 1. Recommended Load Impedance at OUT or OUT for Optimum Power Transfer 4 FREQUENCY (MHz) REAL COMPONENT (R in Ω) IMAGINARY COMPONENT (X in Ω) 250 106 163 350 68 102 450 60 96 550 35 79 650 17.5 62.3 750 17.2 50.6 850 10.9 33.1 950 7.3 26.3 1050 6.5 22.7 _______________________________________________________________________________________ 10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs (Per Typical Operating Circuit, VCC = +3.0V, VTUNE = 1.5V, SHDN = VCC, load at OUT = 50Ω, load at OUT = 50Ω, L1 = coaxial ceramic resonator: Trans-Tech SR8800LPQ1357BY, C6 = 1pF, TA = +25°C, unless otherwise noted.) 900MHz BAND CIRCUIT* TYPICAL 1/S11 vs. FREQUENCY MEASURED AT TEST PORT VCC = 2.7V TO 5.25V C3, C4 REMOVED 0 MAX2620-04 -10 1050MHz 21 + j78 -20 -30 900MHz 36 + j90 -40 -50 800MHz 49 + j105 -60 650MHz 84 + j142 -70 -80 -90 50 250 450 650 850 1050 *SEE FIGURE 1 FREQUENCY (MHz) SUPPLY CURRENT vs. TEMPERATURE 10MHz BAND CIRCUIT TYPICAL 1/S11 vs. FREQUENCY MEASURED AT TEST PORT MAX2620-06 10.0 MAX2620-05 9.5 15MHz 28 + j79.8 10MHz 63.6 + j121.5 5MHz 262 + j261 SUPPLY CURRENT (mA) REVERSE ISOLATION (dB) MAX2620-03 REVERSE ISOLATION vs. FREQUENCY VCC = 5.25V 9.0 VCC = 2.7V 8.5 8.0 7.5 7.0 -40 C3 = C4 = 270pF L3 = 10µH C2 = C10 = C13 = 0.01µF -20 0 20 40 60 80 100 TEMPERATURE (°C) _______________________________________________________________________________________ 5 MAX2620 _____________________________Typical Operating Characteristics (continued) _____________________________Typical Operating Characteristics (continued) (Per Typical Operating Circuit, VCC = +3.0V, VTUNE = 1.5V, SHDN = VCC, load at OUT = 50Ω, load at OUT = 50Ω, L1 = coaxial ceramic resonator: Trans-Tech SR8800LPQ1357BY, C6 = 1pF, TA = +25°C, unless otherwise noted.) OUTPUT SPECTRUM FUNDAMENTAL NORMALIZED TO 0dB -108 L1 = 5nH INDUCTOR C6 = 1.5pF -110 L1 = COAXIAL CERAMIC RESONATOR (TRANS-TECH SR8800LPQ1357BY) C6 = 1pF -114 -20 -30 -40 -50 -60 -70 -20 0 20 40 TEMPERATURE (°C) 60 80 L1 = 5nH INDUCTOR C6 = 1.5pF -60 -70 -80 -90 -100 -110 L1 = COAXIAL CERAMIC RESONATOR (TRANS-TECH SR8800LPQ1357BY) C6 = 1pF -120 -80 -130 -90 -140 -100 -40 -50 SSB PHASE NOISE (dBc/Hz) -106 SINGLE SIDEBAND PHASE NOISE -40 MAX2620-08 -10 RELATIVE OUTPUT LEVEL (dBc) SSB @ ∆f = 25kHz -112 0 MAX2620-07 -104 MAX2620-09 PHASE NOISE vs. TEMPERATURE SSB PHASE NOISE (dBc/Hz) MAX2620 10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs -150 0 1.3 2.6 3.9 5.2 6.5 0.1 FREQUENCY (GHz) 1 10 100 1000 OFFSET FREQUENCY (kHz) _______________________________________________________________Pin Description 6 PIN NAME FUNCTION 1 VCC1 Oscillator DC Supply Voltage. Decouple VCC1 with 1000pF capacitor to ground. Use a capacitor with low series inductance (size 0805 or smaller). Further power-supply decoupling can be achieved by adding a 10Ω resistor in series from VCC1 to the supply. Proper power-supply decoupling is critical to the low noise and spurious performance of any oscillator. 2 TANK Oscillator Tank Circuit Connection. Refer to the Applications Information section. 3 FDBK Oscillator Feedback Circuit Connection. Connecting capacitors of the appropriate value between FDBK and TANK and between FDBK and GND tunes the oscillator’s reflection gain (negative resistance) to peak at the desired oscillation frequency. Refer to the Applications Information section. 4 SHDN Logic-Controlled Input. A low level turns off the entire circuitry such that the IC will draw only leakage current at its supply pins. This is a high-impedance input. 5 OUT Open-Collector Output Buffer (complement). Requires external pull-up to the voltage supply. Pull-up can be resistor, choke, or inductor (which is part of a matching network). The matching-circuit approach provides the highest-power output and greatest efficiency. Refer to Table 1 and the Applications Information section. OUT may be used with OUT in a differential output configuration. 6 GND Ground Connection. Provide a low-inductance connection to the circuit ground plane. 7 VCC2 Output Buffer DC Supply Voltage. Decouple VCC2 with a 1000pF capacitor to ground. Use a capacitor with low series inductance (size 0805 or smaller). 8 OUT Open-Collector Output Buffer. Requires external pull-up to the voltage supply. Pull-up can be resistor, choke, or inductor (which is part of a matching network). The matching-circuit approach provides the highest-power output and greatest efficiency. Refer to Table 1 and the Applications Information section. OUT may be used with OUT in a differential output configuration. _______________________________________________________________________________________ 10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs MAX2620 VCC 10Ω VCC 1000pF 1 VCC1 TEST PORT C2* 1000pF VCC ON 1000pF L3* 220nH MAX2620 2 TANK VCC2 7 C3* 2.7pF 3 FDBK GND 6 C4* 1pF 4 SHDN BIAS SUPPLY C13* 1000pF OUT OUT 8 ZO = 50Ω VCC 1000pF C10* 1000pF OUT OUT 5 ZO = 50Ω 51Ω OFF VCC 10Ω 1000pF 1000pF *AT 10MHz, CHANGE TO: C3 = C4 = 270pF L3 = 10µH C2 = C10 = C13 = 0.01µF Figure 1. 900MHz Test Circuit _______________Detailed Description __________Applications Information Oscillator Design Principles The oscillator is a common-collector, negativeresistance type that uses the IC’s internal parasitic elements to create a negative resistance at the baseemitter port. The transistor oscillator has been optimized for low-noise operation. Base and emitter leads are provided as external connections for a feedback capacitor and resonator. A resonant circuit, tuned to the appropriate frequency and connected to the base lead, will cause oscillation. Varactor diodes may be used in the resonant circuit to create a voltage-controlled oscillator (VCO). The oscillator is internally biased to an optimal operating point, and the base and emitter leads need to be capacitively coupled due to the bias voltages present. At the frequency of interest, the MAX2620 portion of Figure 2 shows the one-port circuit model for the TANK pin (test port in Figure 1). For the circuit to oscillate at a desired frequency, the resonant tank circuit connected to TANK must present an impedance that is a complement to the network (Figure 2). This resonant tank circuit must have a positive real component that is a maximum of one-half the magnitude of the negative real part of the oscillator device, as well as a reactive component that is opposite in sign to the reactive component of the oscillator device. Output Buffers The output buffers (OUT and OUT) are an opencollector, differential-pair configuration and provide load isolation to the oscillator. The outputs can be used differentially to drive an integrated circuit mixer. Alternatively, isolation is provided between the buffer outputs when one output drives a mixer (either upconversion or downconversion) and the other output drives a prescaler. The isolation in this configuration prevents prescaler noise from corrupting the oscillator signal’s spectral purity. A logic-controlled SHDN pin turns off all bias to the IC when pulled low. TANK LESS THAN 1/2 TIMES RL jXL RESONANT TANK -jXT -Rn OSCILLATOR DEVICE Figure 2. Simplified Oscillator Circuit Model _______________________________________________________________________________________ 7 MAX2620 10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs Keeping the resonant tank circuit’s real component less than one-half the magnitude of the negative real component ensures that oscillations will start. After start-up, the oscillator’s negative resistance decreases, primarily due to gain compression, and reaches equilibrium with the real component (the circuit losses) in the resonant tank circuit. Making the resonant tank circuit reactance tunable (e.g., through use of a varactor diode) allows for tuneability of the oscillation frequency, as long as the oscillator exhibits negative resistance over the desired tuning range. See Figures 3 and 4. The negative resistance of the MAX2620 TANK pin can be optimized at the desired oscillator frequency by proper selection of feedback capacitors C3 and C4. For example, the one-port characteristics of the device are given as a plot of 1/S11 in the Typical Operating Characteristics. 1/S11 is used because it maps inside the unit circle Smith chart when the device exhibits negative resistance (reflection gain). VCC VCC 1000pF 10Ω 1000pF 10µH 1 VTUNE VCC1 2 1k C3 270pF C6 33pH 0.01µF 8 OUT TO MIXER VCC C5 150pF C17 33pF OUT 27pF 3 L1 2.2µH C4 270pF D1 4 MAX2620 TANK VCC2 FDBK GND SHDN OUT 7 1000pF 6 0.01µF 5 OUT TO SYNTHESIZER SHDN 51Ω 1000pF D1 = SMV1200-155 DUAL VARACTOR VCC Figure 3. 10MHz VCO LC Resonator 8 _______________________________________________________________________________________ 10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs Rn, the negative real impedance, is set by C3 and C4 and is approximately: [Equation 2] 1 1 R n = gm 2πfC 3 2πfC4 VCC 0.01µF 10Ω 0.01µF where gm = 0.018mS. Using the circuit model of Figure 5, the following example describes the design of an oscillator centered at 900MHz. Choose: L1 = 5nH ±10% Q = 140 Calculate Rp = Q x 2π x f x L1 Using Equation 1, solve for varactor capacitance (CD1). CD1 is the capacitance of the varactor when the voltage applied to the varactor is approximately at halfsupply (the center of the varactor’s capacitance range). Assume the following values: CSTRAY = 2.7pF, C17 = 1.5pF, C6 = 1.5pF, C5 = 1.5pF, C3 = 2.7pF, and C4 = 1pF. The value of CSTRAY was based on approximate performance of the MAX2620 EV kit. Values of C3 and C4 are chosen to minimize Rn (Equation 2) while not loading the resonant circuit with excessive capacitance. 27pF 10µH 0.01µF 1 30pF 120pF 2 3 4 120pF VCC1 OUT TANK VCC2 MAX2620 FDBK GND SHDN OUT 8 OUT VCC 7 0.01µF 6 0.01µF 5 OUT 51Ω 0.01µF SHDN VCC X = STATEK AT-3004 10MHz FUNDAMENTAL MODE CRYSTAL SURFACE MOUNT CLOAD = 20pF The varactor’s capacitance range should allow for the desired tuning range. Across the tuning frequency range, ensure that Rp < 1/2 Rn. Figure 4. 10MHz Crystal Oscillator The MAX2620’s oscillator is optimized for low-phasenoise operation. Achieving lowest phase-noise characteristics requires the use of high-Q (quality factor) components such as ceramic transmission-line type resonators or high-Q inductors. Also, keep C5 and C17 Example Calculation According to the electrical model shown in Figure 5, the resonance frequency can be calculated as: [Equation 1] fO = 1 ( )( ) C 3 + C 03 C4 + C 04 C x CD1 2π L1 CSTRAY + 17 + C6 + C17 + CD1 C 3 + C 03 + C4 + C 04 _______________________________________________________________________________________ 9 MAX2620 VCC MAX2620 10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs TEST PORT MEASUREMENT (FIGURE 1) MAX2620 C5 C17 CSTRAY L1 Rp VARACTOR+ COUPLING C03 2.4pF C4 C04 2.4pF Rn C6 CD1 PCB PARASITICS C3 INDUCTOR OR CERAMIC RESONATOR MAX2620 PACKAGE MODEL RESONANT TANK MODEL Figure 5. Electrical Model of MAX2620 Circuit (see Typical Operating Circuit) as small a value as possible while still maintaining desired frequency and tuning range to maximize loaded Q. There are many good references on the topic of oscillator design. An excellent reference is “The Oscillator as a Reflection Amplifier, an Intuitive Approach to Oscillator Design,” by John W. Boyles, Microwave Journal, June 1986, pp. 83–98. Output Matching Configuration Both of the MAX2620’s outputs (OUT and OUT) are open collectors. They need to be pulled up to the supply by external components. An easy approach to this pull-up is a resistor. A 50Ω resistor value would inherently match the output to a 50Ω system. The Typical Operating Circuit shows OUT configured this way. Alternatively, a choke pull-up (Figure 1), yields greater output power (approximately -8dBm at 900MHz). When maximum power is required, use an inductor as the supply pull-up, and match the inductor’s output impedance to the desired system impedance. Table 1 in the Typical Operating Characteristics shows recommended load impedance presented to OUT and OUT 10 __________________Pin Configuration TOP VIEW VCC1 1 8 OUT TANK 2 7 VCC2 6 GND 5 OUT FDBK 3 MAX2620 SHDN 4 µMAX for maximum power transfer. Using this data and standard matching-network synthesis techniques, a matching network can be constructed that will optimize power output into most load impedances. The value of the inductor used for pull-up should be used in the synthesis of the matching network. ______________________________________________________________________________________ 10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs 8LUMAXD.EPS ______________________________________________________________________________________ 11 MAX2620 ________________________________________________________Package Information MAX2620 10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs NOTES 12 ______________________________________________________________________________________