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19-1248; Rev 1; 5/98
KIT ATION EVALU BLE AVAILA
10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs
____________________________Features
Low-Phase-Noise Oscillator: -110dBc/Hz (25kHz offset from carrier) Attainable 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: 0.1A (typ)
_________________General Description
The MAX2620 combines a low-noise oscillator with two output buffers in a low-cost, plastic surface-mount, ultra-small MAX 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 0.3W in standby mode. The MAX2620 operates from a single +2.7V to +5.25V supply.
MAX2620
________________________Applications
Analog Cellular Phones Digital Cellular Phones 900MHz Cordless Phones 900MHz ISM-Band Applications Land Mobile Radio Narrowband PCS (NPCS)
_______________Ordering Information
PART MAX2620EUA MAX2620E/D TEMP. RANGE -40C to +85C -40C to +85C PIN-PACKAGE 8 MAX Dice*
*Dice are tested at TA = +25C, DC parameters only.
Pin Configuration appears at end of data sheet.
____________________________________________________Typical Operating Circuit
VCC 10 1000pF 10nH 1000pF 1 VCC1 C17 1.5pF VTUNE 1k D1 ALPHA SMV1204-34 CERAMIC RESONATOR L1 C6 C4 1pF 4 SHDN BIAS SUPPLY C3 2.7pF C5 1.5pF 2 TANK 3 FDBK OUT 8 1.5pF VCC
MAX2620
VCC2 7 GND 6 0.1F
OUT TO MIXER VCC
OUT 5
1000pF OUT TO SYNTHESIZER 51
SHDN 1000pF
VCC
900MHz BAND OSCILLATOR
________________________________________________________________ Maxim Integrated Products
1
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10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs MAX2620
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 = +70C) MAX (derate 5.7mW/C above +70C) .....................457mW Operating Temperature Range MAX2620EUA .................................................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +165C Lead Temperature (soldering, 10sec) .............................+300C
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 50, SHDN = 2V, TA = -40C to +85C, unless otherwise noted. Typical values measured at VCC1 = VCC2 = 3.0V, TA = +25C.) (Note 1) PARAMETER Supply Current Shutdown Current Shutdown Input Voltage High Shutdown Input Voltage Low Shutdown Bias Current High Shutdown Bias Current Low SHDN = 2.0V SHDN = 0.6V 5.5 SHDN = 0.6V 2.0 0.6 20 0.5 CONDITIONS MIN TYP 9.0 0.1 MAX 12.5 2 UNITS mA A V V A A
Note 1: Specifications are production tested and guaranteed at TA = +25C and TA = +85C. Specifications are guaranteed by design and characterization at TA = -40C.
AC ELECTRICAL CHARACTERISTICS
(Per Test Circuit of Figure 1, VCC = +3.0V, SHDN = VCC, ZLOAD = ZSOURCE = 50, PIN = -20dBm (50), fTEST = 900MHz, TA = +25C, unless otherwise noted.) PARAMETER Frequency Range Reverse Isolation Output Isolation CONDITIONS TA = -40C to +85C (Note 2) OUT or OUT to TANK; OUT, OUT driven at P = -20dBm OUT to OUT MIN 10 50 33 TYP MAX 1050 UNITS MHz dB 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.
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10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs
TYPICAL OPERATING CIRCUIT PERFORMANCE--900MHz Band CeramicResonator-Based Tank
(Per Typical Operating Circuit, VCC = +3.0V, VTUNE = 1.5V, SHDN = VCC, load at OUT = 50, load at OUT = 50, L1 = coaxial ceramic resonator: Trans-Tech SR8800LPQ1357BY, C6 = 1pF, TA = +25C, unless otherwise noted.) PARAMETER Tuning Range Phase Noise VTUNE = 0.5V to 3.0V SSB @ f = 25kHz SSB @ f = 300kHz At OUT (Note 2) Output Power (single-ended) At OUT, per test circuit of Figure 1; TA = -40C to +85C (Note 3) At OUT (Note 3) Noise Power Average Tuning Gain Second-Harmonic Output Load Pull Supply Pushing VSWR = 1.75:1, all phases VCC stepped from 3V to 4V fO >10MHz -6 -11 -16 CONDITIONS MIN TYP 13 -110 -132 -2 -8 -12.5 -147 11 -29 163 71 dBm/Hz MHz/V dBc kHzp-p kHz/V dBm MAX UNITS MHz dBc/Hz
MAX2620
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 = 50, load at OUT = 50, L1 = 5nH (Coilcraft A02T), C6 = 1.5pF, TA = +25C, unless otherwise noted.) PARAMETER Tuning Range Phase Noise VTUNE = 0.5V to 3.0V SSB @ f = 25kHz SSB @ f = 300kHz At OUT (Note 2) Output Power (single-ended) At OUT, per test circuit of Figure 1; TA = -40C to +85C (Note 3) At OUT (Note 3) Noise Power Average Tuning Gain Second-Harmonic Output Load Pull Supply Pushing VSWR = 1.75:1, all phase angles VCC stepped from 3V to 4V fO >10MHz -6 -11 -16 CONDITIONS MIN TYP 15 -107 -127 -2 -8 -12.5 -147 13 -29 340 150 dBm/Hz MHz/V dBc kHzp-p kHz/V dBm MAX UNITS MHz dBc/Hz
Note 3: Guaranteed by design and characterization.
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10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs MAX2620
__________________________________________Typical Operating Characteristics
(Per test circuit of Figure 1, VCC = +3.0V, SHDN = VCC, ZLOAD = ZSOURCE = 50, PIN = -20dBm/50, fTEST = 900MHz, TA = +25C, unless otherwise noted.)
OUT OUTPUT POWER vs. FREQUENCY OVER VCC AND TEMPERATURE
-5 VCC = 5.25V -6 POWER (dBm) C VCC = 5.25V
MAX2620-01
OUT OUTPUT POWER vs. FREQUENCY OVER VCC AND TEMPERATURE
-11.0 TA = +85C TA = +25C TA = -40C POWER (dBm) VCC = 5.25V -11.5 TA = +25C -12.0 TA = -40C -12.5 VCC = 2.7V -13.0
MAX2620-02
TA = +85C
-7
VCC = 2.7V A B VCC = 2.7V
-8
-9 0 200 400 600 800 1000 1200 FREQUENCY (MHz) A: 10MHz BAND CIRCUIT B: NOT CHARACTERIZED FOR THIS FREQUENCY BAND. EXPECTED PERFORMANCE SHOWN. C: 900MHz BAND CIRCUIT
-13.5 0 200 400 600 800 1000 1200 FREQUENCY (MHz)
Table 1. Recommended Load Impedance at OUT or OUT for Optimum Power Transfer
FREQUENCY (MHz) 250 350 450 550 650 750 850 950 1050 REAL COMPONENT (R in ) 106 68 60 35 17.5 17.2 10.9 7.3 6.5 IMAGINARY COMPONENT (X in ) 163 102 96 79 62.3 50.6 33.1 26.3 22.7
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10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs MAX2620
_____________________________Typical Operating Characteristics (continued)
(Per Typical Operating Circuit, VCC = +3.0V, VTUNE = 1.5V, SHDN = VCC, load at OUT = 50, load at OUT = 50, L1 = coaxial ceramic resonator: Trans-Tech SR8800LPQ1357BY, C6 = 1pF, TA = +25C, unless otherwise noted.)
REVERSE ISOLATION vs. FREQUENCY
0 REVERSE ISOLATION (dB) -10 -20 -30 -40 -50 -60 -70 -80 -90 50 250 450 650 850 1050 *SEE FIGURE 1 FREQUENCY (MHz) VCC = 2.7V TO 5.25V C3, C4 REMOVED
MAX2620-03
900MHz BAND CIRCUIT* TYPICAL 1/S11 vs. FREQUENCY MEASURED AT TEST PORT
MAX2620-04
1050MHz 21 + j78 900MHz 36 + j90 800MHz 49 + j105 650MHz 84 + j142
MAX2620-05
9.5 15MHz 28 + j79.8 10MHz 63.6 + j121.5 5MHz 262 + j261 SUPPLY CURRENT (mA) VCC = 5.25V 9.0 VCC = 2.7V 8.5 8.0 7.5 7.0 -40 C3 = C4 = 270pF L3 = 10H C2 = C10 = C13 = 0.01F -20 0 20 40 60 80 100 TEMPERATURE (C)
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MAX2620-06
10MHz BAND CIRCUIT TYPICAL 1/S11 vs. FREQUENCY MEASURED AT TEST PORT
SUPPLY CURRENT vs. TEMPERATURE
10.0
5
10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs MAX2620
_____________________________Typical Operating Characteristics (continued)
(Per Typical Operating Circuit, VCC = +3.0V, VTUNE = 1.5V, SHDN = VCC, load at OUT = 50, load at OUT = 50, L1 = coaxial ceramic resonator: Trans-Tech SR8800LPQ1357BY, C6 = 1pF, TA = +25C, unless otherwise noted.)
OUTPUT SPECTRUM FUNDAMENTAL NORMALIZED TO 0dB
MAX2620-07 MAX2620-08
PHASE NOISE vs. TEMPERATURE
-104 SSB @ f = 25kHz 0 -10 RELATIVE OUTPUT LEVEL (dBc) -20 -30 -40 -50 -60 -70 -80 -90 -100 -40 -20 0 20 40 60 80 0
SINGLE SIDEBAND PHASE NOISE
-50 SSB PHASE NOISE (dBc/Hz) -60 -70 -80 -90 -100 -110 -120 -130 -140 -150 L1 = COAXIAL CERAMIC RESONATOR (TRANS-TECH SR8800LPQ1357BY) C6 = 1pF 0.1 1 10 100 1000 L1 = 5nH INDUCTOR C6 = 1.5pF
MAX2620-09
-40
SSB PHASE NOISE (dBc/Hz)
-106
-108 L1 = 5nH INDUCTOR C6 = 1.5pF -110 L1 = COAXIAL CERAMIC RESONATOR (TRANS-TECH SR8800LPQ1357BY) C6 = 1pF
-112
-114 TEMPERATURE (C)
1.3
2.6
3.9
5.2
6.5
FREQUENCY (GHz)
OFFSET FREQUENCY (kHz)
_______________________________________________________________Pin Description
PIN NAME FUNCTION 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 10 resistor in series from VCC1 to the supply. Proper power-supply decoupling is critical to the low noise and spurious performance of any oscillator. Oscillator Tank Circuit Connection. Refer to the Applications Information section. 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. 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. 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. Ground Connection. Provide a low-inductance connection to the circuit ground plane. Output Buffer DC Supply Voltage. Decouple VCC2 with a 1000pF capacitor to ground. Use a capacitor with low series inductance (size 0805 or smaller). 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.
1
VCC1
2 3
TANK FDBK
4
SHDN
5
OUT
6 7
GND VCC2
8
OUT
6
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10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs MAX2620
VCC 10 VCC L3* 220nH 1 VCC1 2 TANK C2* 1000pF VCC ON C3* 2.7pF C4* 1pF 3 FDBK 4 SHDN BIAS SUPPLY 1000pF C13* 1000pF VCC 1000pF C10* 1000pF OUT ZO = 50 51 VCC 10 1000pF 1000pF *AT 10MHz, CHANGE TO: C3 = C4 = 270pF L3 = 10H C2 = C10 = C13 = 0.01F
1000pF TEST PORT
MAX2620
OUT 8 VCC2 7 GND 6 OUT 5
OUT ZO = 50
OFF
Figure 1. 900MHz Test Circuit
_______________Detailed Description
Oscillator
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.
__________Applications Information
Design Principles
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 -jXT -Rn
RESONANT TANK
OSCILLATOR DEVICE
Figure 2. Simplified Oscillator Circuit Model
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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.
MAX2620
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 10 1000pF 10H 27pF
VTUNE C5 150pF
1
VCC1
OUT
8 VCC
0.01F OUT TO MIXER
2 1k C17 33pF C6 33pH L1 2.2H C4 270pF D1 4 C3 270pF 3
MAX2620
TANK VCC2
7
FDBK
GND
6
1000pF
SHDN
OUT
5
0.01F OUT TO SYNTHESIZER
SHDN
51 1000pF
D1 = SMV1200-155 DUAL VARACTOR
VCC
Figure 3. 10MHz VCO LC Resonator
8
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10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs
VCC VCC 0.01F 10 0.01F 10H 27pF
Rn, the negative real impedance, is set by C3 and C4 and is approximately: [Equation 2] 1 1 R n = gm 2fC 3 2fC4 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 2 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. The varactor's capacitance range should allow for the desired tuning range. Across the tuning frequency range, ensure that Rp < 1/2 Rn. 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 1
MAX2620
0.01F 1 30pF 2 VCC1 TANK OUT VCC2 8 VCC 7 0.01F OUT
120pF
3
MAX2620
FDBK GND
6
4 120pF
SHDN
OUT
5
0.01F OUT 51
SHDN
0.01F
VCC X = STATEK AT-3004 10MHz FUNDAMENTAL MODE CRYSTAL SURFACE MOUNT CLOAD = 20pF
Figure 4. 10MHz Crystal Oscillator
Example Calculation
According to the electrical model shown in Figure 5, the resonance frequency can be calculated as: [Equation 1] fO =
C 3 + C 03 C4 + C 04 C x CD1 2 L1 CSTRAY + 17 + C6 + C17 + CD1 C 3 + C 03 + C4 + C 04
(
)(
)

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9
10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs MAX2620
TEST PORT MEASUREMENT (FIGURE 1) C5
MAX2620
C17 CSTRAY CD1 PCB PARASITICS VARACTOR+ COUPLING INDUCTOR OR CERAMIC RESONATOR L1 Rp C6
C3
C03 2.4pF
Rn
C4
C04 2.4pF
RESONANT TANK MODEL
MAX2620 PACKAGE 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.
__________________Pin Configuration
TOP VIEW
VCC1 1 TANK 2 FDBK 3 SHDN 4
8
OUT VCC2 GND OUT
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 50 resistor value would inherently match the output to a 50 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
MAX2620
7 6 5
MAX
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.
10
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10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs MAX2620
________________________________________________________Package Information
8LUMAXD.EPS
______________________________________________________________________________________
11
10MHz to 1050MHz Integrated RF Oscillator with Buffered Outputs MAX2620
NOTES
12
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