MAXIM MAX2620

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
______________________________________________________________________________________