19-1673; Rev 0a; 4/02 45MHz to 650MHz, Integrated IF
EVALUAATVIOANILKAIBTLMEANUAL VCOs with Differential Output
General Description Features MAX2605�MAX2609
The MAX2605�MAX2609 are compact, high-performance o Small Size
intermediate-frequency (IF) voltage-controlled oscillators o Integrated Varactor for Tuning
(VCOs) designed specifically for demanding portable o Low Phase Noise
wireless communication systems. They combine monolith- o Wide Application Frequency Range
ic construction with low-noise, low-power operation in a o Differential or Single-Ended Outputs
tiny 6-pin SOT23 package. o Single +2.7V to +5.5V Supply
o Ultra-Small SOT23-6 Package
These low-noise VCOs feature an on-chip varactor and o On-Chip Temperature-Stable Bias
feedback capacitors that eliminate the need for external o Low-Current Operation
tuning elements, making the MAX2605�MAX2609 ideal
for portable systems. Only an external inductor is Ordering Information
required to set the oscillation frequency. In addition, an
integrated differential output buffer is provided for dri- PART TEMP. RANGE PIN- TOP
ving a mixer or prescaler. The buffer output is capable PACKAGE MARK
of supplying up to -8dBm (differential) with a simple MAX2605EUT-T -40�C to +85�C
power match. It also provides isolation from load MAX2606EUT-T -40�C to +85�C 6 SOT23-6 AABB
impedance variations. MAX2607EUT-T -40�C to +85�C 6 SOT23-6 AABC
MAX2608EUT-T -40�C to +85�C 6 SOT23-6 AABD
The MAX2605�MAX2609 operate from a single +2.7V to MAX2609EUT-T -40�C to +85�C 6 SOT23-6 AABE
+5.5V supply and offer low current consumption. These IF 6 SOT23-6 AABF
oscillators can cover the 45MHz to 650MHz frequency
range.
Applications
Cellular and PCS Mobile Phones
2.4GHz ISM Band
902MHz to 928MHz ISM Band
Land Mobile Radio
GPS Receivers
General-Purpose IF Oscillators
Selector Guide Pin Configuration/
Functional Diagram
PART FREQUENCY SUPPLY PHASE TOP VIEW MAX2605 6 OUT+
RANGE CURRENT NOISE MAX2606 5 VCC
MAX2605 (MHz) (dBc/Hz) IND 1 MAX2607 4 OUT-
MAX2606 (mA) GND 2 MAX2608
MAX2607 45 to 70 -117 TUNE 3 MAX2609
MAX2608 70 to 150 1.9 -112
MAX2609 150 to 300 2.1 -107
300 to 500 2.1 -100
500 to 650 2.7 -93
3.6
SOT23-6
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim's website at www.maxim-ic.com.
45MHz to 650MHz, Integrated IF
VCOs with Differential Output
MAX2605�MAX2609 ABSOLUTE MAXIMUM RATINGS Operating Temperature Range ...........................-40�C to +85�C
Junction Temperature ......................................................+150�C
VCC to GND ..............................................................-0.3V to +6V Storage Temperature Range .............................-65�C to +150�C
IND to GND ................................................-0.6V to (VCC + 0.3V) Lead Temperature (soldering, 10s) .................................+300�C
TUNE to GND .............................................-0.3V to (VCC + 0.3V)
OUT+, OUT- to GND ..................................-0.3V to (VCC + 0.6V)
Continuous Power Dissipation (TA = +85�C)
6-Pin SOT23 (derate 8.7mW/�C above +70�C) ...........696mW
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
(VCC = +2.7V to +5.5V, VTUNE = 0.4V to 2.4V, TA = -40�C to +85�C, unless otherwise noted. Typical values are at VCC = +2.75V,
VTUNE = 1.5V, and TA = +25�C.) (Note1)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Supply Voltage
2.7 5.5 V
Supply Current (Note 2)
MAX2605 TA = +25�C 1.9 2.6
DC Output Current (Note 3) MAX2606 TA = -40�C to +85�C
TUNE Input Current MAX2607 TA = +25�C 2.8
MAX2608 TA = -40�C to +85�C
MAX2609 TA = +25�C 2.1 2.7
OUT+ plus OUT- TA = -40�C to +85�C
TA = +25�C 3.0
TA = -40�C to +85�C
TA = +25�C 2.1 3.2
TA = -40�C to +85�C
3.5 mA
2.7 4.4
5.5
3.6 6.8
7.5
0.5 1.0 1.5 mA
0.03 nA
2 _______________________________________________________________________________________
45MHz to 650MHz, Integrated IF
VCOs with Differential Output
AC ELECTRICAL CHARACTERISTICS MAX2605�MAX2609
(MAX2605�MAX2609 EV kits, VCC = +2.7V to +5.5V, VTUNE = 0.4V to 2.4V, TA = -40�C to +85�C, unless otherwise noted. Typical val-
ues are at VCC = +2.75V, VTUNE = 1.5V, and TA = +25�C.) (Note 1)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Oscillator Nominal Frequency 45 70 MHz
Range (Note 4) MAX2605 70 14.5 150
150 -10 300 %
Guaranteed Frequency Limits MAX2606 300 -117 500
(relative to nominal) (Note 5) 500 -112 650 %/V
MAX2607 -4.1 -107 +3.2 dBm
Peak Tuning Gain -2.25 -100 dBc/Hz
Single-Ended Output Power MAX2608 -4.4 -93 +2.25
(Note 7) -2.5 +3.4
Phase Noise (Note 8) MAX2609 -4.6 +2.5
-2.75 +3.6
MAX2605 TA = +25�C -4.7 +2.75
TA = -40�C to +85�C -2.8 +3.6
-5.0 +2.8
MAX2606 TA = +25�C -3.0 +3.8
MAX2607 TA = -40�C to +85�C +3.0
MAX2608 TA = +25�C
TA = -40�C to +85�C
TA = +25�C
TA = -40�C to +85�C
MAX2609 TA = +25�C
TA = -40�C to +85�C
VTUNE = 0.4V to 0.6V step (Note 6)
fOFFSET = 100kHz MAX2605, QL 35
MAX2606, QL 35
MAX2607, QL 35
MAX2608, QL 40
MAX2609, QL 40
_______________________________________________________________________________________ 3
45MHz to 650MHz, Integrated IF
VCOs with Differential Output
MAX2605�MAX2609 AC ELECTRICAL CHARACTERISTICS (continued)
(MAX2605�MAX2609 EV kits, VCC = +2.7V to +5.5V, VTUNE = 0.4V to 2.4V, TA = -40�C to +85�C, unless otherwise noted. Typical val-
ues are at VCC = +2.75V, VTUNE = 1.5V, and TA = +25�C.) (Note 1)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Even-Order Harmonics Differential, RL = 50 each side
MAX2605 -30 dBc
Supply Pushing (Note 9) MAX2606
MAX2607 60
MAX2608
MAX2609 120
220 kHz/V
480
720
Note 1: Production tested at TA = +25�C. Maximum and minimum over temperature limits are guaranteed by design and
characterization.
Note 2: Supply current is measured while the part is oscillating and inductor Q QMIN. For MAX2605/MAX2606/MAX2607, QMIN = 35;
for MAX2608/MAX2609, QMIN = 40.
Note 3: The DC output current is the total available output signal current.
Note 4: Application range of the part is achieved using external inductance as specified in Figures 1-5 and shown in Figure 6. The inter-
nal varactors support center frequencies of 45MHz to 650MHz. The center frequency is defined by the value of the external
inductor element, LF. The application frequency limits are guaranteed by design and characterization.
Note 5: The guaranteed (tested) limits MIN and MAX are measured at VTUNE = 0.4V and VTUNE = 2.4V, respectively. Passing
requirements are: MIN at VTUNE = 0.4 and MAX at VTUNE = 2.4V. The nominal frequency of oscillation is defined by
the inductor.
Note 6: Describes peak tuning gain, which occurs at VTUNE = 0.4V.
Note 7: Measurement at OUT+ or OUT- matched for optimum power transfer into 50 load near the center of the operating frequency
range.
Note 8: The phase-noise specifications listed apply to the typical operating circuit shown in Figure 6. Apply over the entire operating
frequency range of the MAX2605�MAX2609.
Note 9: Supply pushing is measured with VCC stepped from +2.7V to +3.2V.
Typical Operating Characteristics
(MAX260_ EV kit, VCC = +2.75V, VTUNE = 1.4V, TA = +25�C, unless otherwise noted.)
SUPPLY CURRENT TUNE INPUT LEAKAGE CURRENT MAX2605
vs. TEMPERATURE vs. TEMPERATURE VCO TUNING CURVE
4.0 0.10 65
SUPPLY CURRENT (mA)
MAX2605/9-01
LEAKAGE CURRENT (nA)
MAX2605/9-02
FREQUENCY (MHz)
MAX2605/9-03
3.5 0.08 60
MAX2609
0.06
3.0 MAX2608 MAX2607 MAX2606
0.04
2.5 55
0.02
2.0
0
-40 -20 0 20 40 60 80 50
TEMPERATURE (�C)
1.5 MAX2605
1.0 45 0.5 1.0 1.5 2.0 2.5 3.0
-40 -20 0 20 40 60 80 0 VTUNE (V)
TEMPERATURE (�C)
4 _______________________________________________________________________________________
45MHz to 650MHz, Integrated IF
VCOs with Differential Output
Typical Operating Characteristics (continued) MAX2605�MAX2609
(MAX260_ EV kit, VCC = +2.75V, VTUNE = 1.4V, TA = +25�C, unless otherwise noted.)
MAX2606 MAX2607 MAX2608
VCO TUNING CURVE VCO TUNING CURVE VCO TUNING CURVE
130 260 430
FREQUENCY (MHz)
MAX2605/9-04240
FREQUENCY (MHz)120 400
MAX2605/9-05
220
FREQUENCY (MHz)
MAX2605/9-06110370
200
100 180 340
90 0.5 1.0 1.5 2.0 2.5 3.0 160 0.5 1.0 1.5 2.0 2.5 3.0 310 0.5 1.0 1.5 2.0 2.5 3.0
0 0 0
VTUNE (V) VTUNE (V) VTUNE (V)
MAX2609 MAX2605/9-07 OUTPUT SPECTRUM MAX2605/9-08
VCO TUNING CURVE
0
680
640 -10
FREQUENCY (MHz) 600 -20
(dB)
560 -30
520 -40
480 0.5 1.0 1.5 2.0 2.5 3.0 -50
0 VTUNE (V) fo 2fo 3fo 4fo 5fo 6fo 7fo
FREQUENCY
Pin Description
PIN NAME FUNCTION
1 IND Tuning Inductor Port. Connect an inductor from IND to GND to set VCO center frequency (see Oscillation
Frequency).
2 GND Ground. Connect to the ground plane with a low-inductance path.
3 TUNE Voltage-Control Input for Frequency Tuning. Input voltage range from +0.4V to +2.4V.
4 OUT- High-Impedance Open-Collector Output. An external pull-up resistor or inductor to VCC is required. Output
power is dependent on external load impedance. OUT- is complementary to OUT+.
5 VCC Supply Voltage Connection. Connect an external bypass capacitor to ground for low noise and low spuri-
ous-output content. See Layout Issues for more details.
6 OUT+ High-Impedance Open-Collector Output. An external pull-up resistor or inductor to VCC is required. Output
power is dependent on external load impedance. OUT+ is complementary to OUT-.
_______________________________________________________________________________________ 5
45MHz to 650MHz, Integrated IF
VCOs with Differential Output
MAX2605�MAX2609 Detailed Description that required for LF. Choose LF2 to be a standard-value
inductor with a value just less than (LF - LF1). LF1
The MAX2605�MAX2609 are low-noise VCOs designed should adhere to the minimum Q requirements, but LF2
for fixed/single-frequency IF applications. The core may be implemented as a lower-cost, lower-Q, thin-film
oscillator circuit is based on the well-known Colpitts SMT inductor. Its lower Q has only a small impact on
topology. The varactor and feedback capacitors are the overall Q of the total inductance because it is <20%
integrated on-chip so that only an external inductor is of the total inductance. However, the overall Q of LF1
required to establish the frequency of oscillation and and LF2 must be greater than the minimum inductor Q
produce a properly operating VCO. The tuning range, (Table 1).
biasing, startup, etc., are all managed within the IC. This
highly integrated design dramatically simplifies the It is also permissible to use PC board traces to provide
parts' application. a small amount of inductance, thereby adjusting the
total inductance value. On the MAX2608/MAX2609, the
The tuning range is wide enough so that, with the use inductance values for LF2 are sometimes more exactly
of �2% tolerance inductors, no board-level adjustments implemented as a PC board trace (shorted to GND),
to the oscillation frequency are necessary. Once the rather than an SMT inductor. When designing LF with
correct inductor value is chosen, the VCO is guaran- two inductors, use the simple model in Figure 7 to cal-
teed always to tune to the desired operating frequency. culate XL and LEQ.
In addition, with the use of inductors of moderate Q (35
to 40), the VCO achieves excellent phase-noise perfor- The LF in Figures 1�5 represents an equivalent induc-
mance. tance as seen by pin 1 (IND). The equivalent induc-
tance corresponds to the inductive reactance
Applications Information connected to IND at the desired oscillation frequency
(fNOMINAL).
Desired Oscillation Frequency
The desired VCO operating frequency is set by the LEQ = XL / (2 fNOMINAL) as seen in Figure 8
value of the external inductance, LF. Figures 1�5 show
the inductance value LF required to achieve the desired Design LEQ = LF at the desired fNOMINAL. The
oscillation frequency. The inductor value can be taken MAX2605�MAX2609 are designed to tolerate approxi-
directly from these figures. Inductance must be select- mately 0.5pF of external parasitic capacitance at IND.
ed accurately to ensure proper operation over all con- This parasitic capacitance arises from the pad capaci-
ditions. tance at the device pin and pads for the inductor.
Additional shunt capacitance is not recommended
Inductor Implementation because it degrades the tuning range.
The inductance value required for the desired operat-
ing frequency may not necessarily coincide with a stan- Bypass Capacitor on TUNE
dard-value SMT inductor, which typically increases size The MAX2605�MAX2609's oscillator design uses a vari-
in ~1.2x steps. In such cases, the inductance must be ant of the Colpitts topology, where DC bias for the var-
constructed from two inductors, LF1 and LF2, in order to actor is applied via a DC voltage on TUNE and a
achieve the desired inductance value. Choose LF1 to ground connection through the external inductor LF.
be a standard-value inductor with a value just less than TUNE must also have a high-frequency AC ground for
Table 1. External Inductor LF Range Table 2. CBYPASS Values
PART FREQUENCY INDUCTANCE MIN DEVICE CBYPASS
RANGE RANGE INDUCTOR
MAX2605 (MHz) (nH) MAX2605 820 pF
MAX2606 Q MAX2606 680 pF
MAX2607 45 to 70 680 LF 2200 MAX2607 330 pF
MAX2608 70 to 150 150 LF 820 35 MAX2608 100 pF
MAX2609 150 to 300 39 LF 180 35 MAX2609 39 pF
300 to 500 35
500 to 650 10 LF 47 40
3.9 LF 15 40
6 _______________________________________________________________________________________
45MHz to 650MHz, Integrated IF
VCOs with Differential Output
1900 MAX2605 MAX2605�MAX2609
1800 REQUIRED INDUCTANCE vs. DESIRED VCO FIXED FREQUENCY
1700
1600 MEASUREMENT CONDITIONS
VCC = 2.75V, TA = 25�C,
RLOAD = 100||50 (100 RESISTIVE PULL-UP PARALLELED WITH 50
VNA IMPEDANCE), UNUSED OUTPUT TERMINATED IN 50,
PCB PARASITIC SHUNT CAPACITANCE (IND TO GND) = 0.45pF
THE INDUCTANCE LISTED IS THE PRECISE NOMINAL INDUCTANCE VALUE
REQUIRED FROM IND TO GND IN ORDER TO GUARANTEE THE VCO
CAN TUNE TO THE DESIRED FIXED FREQUENCY, OVER ALL OPERATING
CONDITIONS AND WORST-CASE COMPONENT
VALUES (�2% INDUCTOR AND IC PROCESS VARIATION).
1500
REQUIRED INDUCTANCE (nH) 1400
1300
1200
EFFECTIVE INDUCTANCE
FROM IND TO GND
1100
1000 INDUCTOR VALUE
MOUNTED ON EV KIT
900
800
700
45 47 49 51 53 55 57 59 61 63 65 67 69
DESIRED VCO FIXED FREQUENCY (MHz)
Figure 1. MAX2605 Required Inductance vs. Desired VCO Fixed Frequency
_______________________________________________________________________________________ 7
45MHz to 650MHz, Integrated IF
VCOs with Differential Output
MAX2605�MAX2609 MAX2606
REQUIRED INDUCTANCE (nH) REQUIRED INDUCTANCE vs. DESIRED VCO FIXED FREQUENCY
790
MEASUREMENT CONDITIONS
VCC = 2.75V, TA = 25�C,
740 RLOAD = 100||50 (100 RESISTIVE PULL-UP PARALLELED WITH 50
VNA IMPEDANCE), UNUSED OUTPUT TERMINATED IN 50,
PCB PARASITIC SHUNT CAPACITANCE (IND TO GND) = 0.45pF
690 THE INDUCTANCE LISTED IS THE PRECISE NOMINAL INDUCTANCE VALUE
REQUIRED FROM IND TO GND IN ORDER TO GUARANTEE THE VCO
CAN TUNE TO THE DESIRED FIXED FREQUENCY, OVER ALL OPERATING
CONDITIONS AND WORST-CASE COMPONENT
640 VALUES (�2% INDUCTOR AND IC PROCESS VARIATION).
590
540
490
440
390 EFFECTIVE INDUCTANCE
FROM IND TO GND
340
290 INDUCTOR VALUE
MOUNTED ON EV KIT
240
190
140
70 75 80 85 90 95 100 105 110 115 120 125 130 135 140 145 150
DESIRED VCO FIXED FREQUENCY (MHz)
Figure 2. MAX2606 Required Inductance vs. Desired VCO Fixed Frequency
8 _______________________________________________________________________________________
45MHz to 650MHz, Integrated IF
VCOs with Differential Output
MAX2607 MAX2605�MAX2609
REQUIRED INDUCTANCE vs. DESIRED VCO FIXED FREQUENCY
170
MEASUREMENT CONDITIONS
160 VCC = 2.75V, TA = 25�C,
RLOAD = 100||50 (100 RESISTIVE PULL-UP PARALLELED WITH 50
VNA IMPEDANCE), UNUSED OUTPUT TERMINATED IN 50,
PCB PARASITIC SHUNT CAPACITANCE (IND TO GND) = 0.45pF
150
THE INDUCTANCE LISTED IS THE PRECISE NOMINAL INDUCTANCE VALUE
REQUIRED FROM IND TO GND IN ORDER TO GUARANTEE THE VCO
140 CAN TUNE TO THE DESIRED FIXED FREQUENCY, OVER ALL OPERATING
CONDITIONS AND WORST-CASE COMPONENT
VALUES (�2% INDUCTOR AND IC PROCESS VARIATION).
130
REQUIRED INDUCTANCE (nH) 120
110
100
90
80 EFFECTIVE INDUCTANCE
FROM IND TO GND
70
60 INDUCTOR VALUE
MOUNTED ON EV KIT
50
40
30
150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300
DESIRED VCO FIXED FREQUENCY (MHz)
Figure 3. MAX2607 Required Inductance vs. Desired VCO Fixed Frequency
_______________________________________________________________________________________ 9
45MHz to 650MHz, Integrated IF
VCOs with Differential Output
MAX2605�MAX2609 41.0 MAX2608
40.0 REQUIRED INDUCTANCE vs. DESIRED VCO FIXED FREQUENCY
REQUIRED INDUCTANCE (nH) 38.0
37.0 MEASUREMENT CONDITIONS
36.0 VCC = 2.75V, TA = 25�C,
35.0
RLOAD = 100||50 (100 RESISTIVE PULL-UP PARALLELED WITH 50
34.0 VNA IMPEDANCE), UNUSED OUTPUT TERMINATED IN 50,
33.0 PCB PARASITIC SHUNT CAPACITANCE (IND TO GND) = 0.45pF
32.0
31.0 THE INDUCTANCE LISTED IS THE PRECISE NOMINAL INDUCTANCE VALUE
30.0 REQUIRED FROM IND TO GND IN ORDER TO GUARANTEE THE VCO
29.0
28.0 CAN TUNE TO THE DESIRED FIXED FREQUENCY, OVER ALL OPERATING
27.0 CONDITIONS AND WORST-CASE COMPONENT
VALUES (�2% INDUCTOR AND IC PROCESS VARIATION).
26.0
25.0
24.0
23.0
22.0 EFFECTIVE INDUCTANCE
21.0 FROM IND TO GND
20.0
19.0
18.0
17.0
16.0
15.0 INDUCTOR VALUE
14.0 MOUNTED ON EV KIT
13.0
12.0
11.0
10.0
9.0
300 310 320 330 340 350 360 370 380 390 400 410 420 420 430 440 450 460 470 480 490 500
Figure 4. MAX2608 Required Inductance vs. Desired VCO Fixed Frequency
10 ______________________________________________________________________________________
45MHz to 650MHz, Integrated IF
VCOs with Differential Output
REQUIRED INDUCTANCE (nH) 14.0 MAX2609 MAX2605�MAX2609
13.5 REQUIRED INDUCTANCE vs. DESIRED VCO FIXED FREQUENCY
13.0
12.5 MEASUREMENT CONDITIONS
12.0 VCC = 2.75V, TA = 25�C,
11.5
11.0 RLOAD = 100||50 (100 RESISTIVE PULL-UP PARALLELED WITH 50
10.5 VNA IMPEDANCE), UNUSED OUTPUT TERMINATED IN 50,
10.0
9.5 PCB PARASITIC SHUNT CAPACITANCE (IND TO GND) = 0.45pF
9.0
8.5 THE INDUCTANCE LISTED IS THE PRECISE NOMINAL INDUCTANCE VALUE
REQUIRED FROM IND TO GND IN ORDER TO GUARANTEE THE VCO
CAN TUNE TO THE DESIRED FIXED FREQUENCY, OVER ALL OPERATING
CONDITIONS AND WORST-CASE COMPONENT
VALUES (�2% INDUCTOR AND IC PROCESS VARIATION).
EFFECTIVE INDUCTANCE
FROM IND TO GND
8.0
7.5
7.0
6.5
6.0 INDUCTOR VALUE
MOUNTED ON EV KIT
5.5
5.0
4.5
4.0
3.5
500 510 520 530 540 550 560 570 580 590 600 610 620 630 640 650
DESIRED VCO FIXED FREQUENCY (MHz)
Figure 5. MAX2609 Required Inductance vs. Desired VCO Fixed Frequency
______________________________________________________________________________________ 11
45MHz to 650MHz, Integrated IF
VCOs with Differential Output
MAX2605�MAX2609 the cathode of the varactor. This is accomplished from OUT- and OUT+ (in place of resistors) to VCC to
through the use of a simple bypass capacitor connect- provide DC bias for the output stage. The series capac-
ed from TUNE to ground. The value of this capacitor itors are connected from OUT- and OUT+ to the load.
should be greater than or equal to the values listed in The values for LMATCH (Z1 and Z2) and CMATCH (C1
Table 2. and C2) are chosen according to the operating fre-
quency and load impedance. As the output stage is
This capacitor provides an AC "short" to ground for the essentially a high-speed current switch, traditional lin-
internal node of the varactor. It is acceptable to select ear impedance using techniques with [S] parameters
the next-largest standard-value capacitor. Use a do not apply. To achieve a reactive power match, start
capacitor with a low-loss dielectric such as NPO; X7R- with the component values provided in the EV kit, and
based capacitors are not suitable. Omitting this capac- adjust values experimentally.
itor would affect the tuning characteristics of the
MAX2605�MAX2609. Proper operation of the VCOs In general, the differential output may be applied in any
requires the use of this bypass capacitor. manner, as would conventional differential outputs. The
only constraints are the need for a pull-up element to
The MAX2605�MAX2609 VCO is designed to tune over VCC and a voltage swing limit at the output pins OUT-
the full tuning range with a voltage range of 0.4V to and OUT+.
2.4V applied to TUNE. This voltage typically originates
from the output of the phase-locked (PLL) loop filter. Layout Considerations
In general, a properly designed PC board is essential
Output Interface to any RF/microwave circuit or system. Always use con-
The MAX2605�MAX2609 VCO includes a differential trolled impedance lines (microstrip, coplanar wave-
output amplifier after the oscillator core. The amplifier guide, etc.) on high-frequency signals. Always place
stage provides valuable isolation and offers a flexible decoupling capacitors as close to the VCC pin as pos-
interface to the IF stages, such as a mixer and PLL sible. For low phase noise and spurious content, use an
prescaler. The output can be taken single ended or dif- appropriate size decoupling capacitor. For long VCC
ferentially; however, the maximum output power and lines, it may be necessary to add additional decoupling
lowest harmonic output are achieved in the differential capacitors located further from the device. Always pro-
output mode. vide a low-inductance path to ground. Keep the GND
vias as close to the device as possible. In addition, the
Both outputs (OUT- and OUT+) are open-collector VCO should be placed as far away from the noisy sec-
types and require a pull-up element to VCC; this can be tion of a larger system, such as a switching regulator or
either resistive or inductive. A resistor pull-up is the digital circuits. Use star topology to separate the
most straightforward method of interfacing to the out- ground returns.
put, and works well in applications that operate at lower
frequencies or only require a modest voltage swing. The resonator tank circuit (LF) is critical in determining
the VCO's performance. For best performance, use
In Figure 6, Z1 and Z2 are 1k pull-up resistors that are high-Q components and choose values carefully. To
connected from OUT+ and OUT- to VCC, respectively. minimize the effects of parasitic elements, which
These resistors provide DC bias for the output amplifier degrade circuit performance, place LF and CBYP close
and are the maximum value permitted with compliance to their respective pins. Specifically, place CBYP direct-
to the output voltage swing limits. In addition, the 1k ly across pins 2 (GND) and 3 (TUNE).
resistors maximize the swing at the load. DC-blocking
capacitors are connected from OUT- and OUT+ to the For the higher frequency versions, consider the extra
load. If the load driven is primarily resistive and the parasitic inductance and capacitance when determin-
VCO operating frequency is below the -3dB bandwidth ing the oscillation frequency. Be sure to account for the
of the output network, then the peak-to-peak differential following: PC board pad capacitance at IND, PC board
signal amplitude is approximately: pad capacitance at the junction of two series inductors,
series inductance of any PC board traces, and the
( ) VOUTp-p diff = 2 � 1k � RLOAD inductance in the ground return path from the ground-
1mA 1k + RLOAD ed side of the inductor and IC's GND pin. For best
results, connect the "ground" side to the tuning induc-
To optimize the output voltage swing or the output tor as close to pin 2 as possible. In addition, remove
power, use a reactive power match. The matching net- the ground plane around and under LF and CBYP to
work is a simple shunt-inductor series-capacitor circuit, minimize the effects of parasitic capacitance.
as shown in Figure 6. The inductors are connected
12 ______________________________________________________________________________________
45MHz to 650MHz, Integrated IF
VCOs with Differential Output
1 VCC C1 MAX2605�MAX2609
6
LF MAX2605 OUT+ Z1 RLOAD
2 MAX2606 C3 RLOAD
MAX2607 5
CBYP MAX2608 VCC Z2
MAX2609 C2
4
TUNE 3 OUT-
FROM PLL LOOP
FILTER OUTPUT
Figure 6. Typical Operating Circuit
Chip Information
TRANSISTOR COUNT: 158
______________________________________________________________________________________ 13
45MHz to 650MHz, Integrated IF
VCOs with Differential Output
MAX2605�MAX2609 LF1 IND LEQ = XL / 2 NOMINAL
1 IND
CPAR2 LF2 MAX2605 1 MAX2605
CPAR1 MAX2606 MAX2606
MAX2607 XL MAX2607
MAX2608 MAX2608
MAX2609 MAX2609
Figure 7. Simple Model of External Inductance Figure 8. Inductive Reactance at Pin 1 (IND)
MAX2605 VCC
ZL
MAX2606
MAX2607
MAX2608 4
MAX2609
Figure 9. Output Matching Network
14 ______________________________________________________________________________________
45MHz to 650MHz, Integrated IF
VCOs with Differential Output
Package Information
6LSOT.EPS
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