MAX2608EUT+T - Maxim Integrated

AVAILABLE

EVALUATION KIT AVAILABLE

Functional Diagrams

Pin Configurations appear at end of data sheet.

Functional Diagrams continued at end of data sheet.

UCSP is a trademark of Maxim Integrated Products, Inc.

For pricing, delivery, and ordering information, please contact Maxim Direct

at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.

General Description

The MAX2605–MAX2609 are compact, high-performance

intermediate-frequency (IF) voltage-controlled oscillators

(VCOs) designed specifically for demanding portable

wireless communication systems. They combine monolith-

ic construction with low-noise, low-power operation in a

tiny 6-pin SOT23 package.

These low-noise VCOs feature an on-chip varactor and

feedback capacitors that eliminate the need for external

tuning elements, making the MAX2605–MAX2609 ideal

for portable systems. Only an external inductor is

required to set the oscillation frequency. In addition, an

integrated differential output buffer is provided for dri-

ving a mixer or prescaler. The buffer output is capable

of supplying up to -8dBm (differential) with a simple

power match. It also provides isolation from load

impedance variations.

The MAX2605–MAX2609 operate from a single +2.7V to

+5.5V supply and offer low current consumption. These IF

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

Features

♦Small Size

♦Integrated Varactor for Tuning

♦Low Phase Noise

♦Wide Application Frequency Range

♦Differential or Single-Ended Outputs

♦Single +2.7V to +5.5V Supply

♦Ultra-Small SOT23-6 Package

♦On-Chip Temperature-Stable Bias

♦Low-Current Operation

45MHz to 650MHz, Integrated IF

VCOs with Differential Output

GND

OUT-TUNE

16OUT+

5 VCC

IND

MAX2605

MAX2606

MAX2607

MAX2608

MAX2609

SOT23-6

TOP VIEW

19-1673; Rev 0a; 4/02

Pin Configuration/

Functional Diagram

Ordering Information

PART

MAX2605

MAX2606

MAX2607 150 to 300

70 to 150

45 to 70

FREQUENCY

RANGE

(MHz)

SUPPLY

CURRENT

(mA)

1.9

2.1

MAX2608 300 to 500 2.7

PHASE

NOISE

(dBc/Hz)

-117

-112

-107

-100

MAX2609 500 to 650 3.6 -93

Selector Guide

AABE6 SOT23-6-40°C to +85°C

MAX2608EUT-T

AABD

AABC

AABB

TOP

MARK

6 SOT23-6

PIN-

PACKAGE

TEMP. RANGE

-40°C to +85°C

MAX2607EUT-T

MAX2606EUT-T

MAX2605EUT-T

PART

AABF6 SOT23-6-40°C to +85°C

MAX2609EUT-T

MAX2605–MAX2609

45MHz to 650MHz, Integrated IF

VCOs with Differential Output

ABSOLUTE MAXIMUM RATINGS

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)

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.

VCC to GND..............................................................-0.3V to +6V

IND to GND ................................................-0.6V to (VCC + 0.3V)

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

Operating Temperature Range ...........................-40°C to +85°C

Junction Temperature......................................................+150°C

Storage Temperature Range .............................-65°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

MAX2609 TA= -40°C to +85°C

TA= +25°C

7.5

DC Output Current (Note 3) 0.5 1.0 1.5OUT+ plus OUT-

TA= -40°C to +85°C

TA= +25°C

TA= -40°C to +85°C

TA= +25°C

TA= -40°C to +85°C

TA= +25°C

TA= -40°C to +85°C

TA= +25°C

PARAMETER MIN TYP MAX UNITS

3.5

2.1 3.2

3.0

Supply Current (Note 2)

2.1 2.7

2.7 4.4

5.5

3.6 6.8

TUNE Input Current 0.03 nA

Supply Voltage 2.7 5.5 V

1.9 2.6

2.8

CONDITIONS

MAX2607

MAX2606

MAX2608

MAX2605

MAX2605–MAX2609

Maxim Integrated

45MHz to 650MHz, Integrated IF

VCOs with Differential Output

AC ELECTRICAL CHARACTERISTICS

(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)

MAX2609, QL≥40

Peak Tuning Gain 14.5 %/VVTUNE = 0.4V to 0.6V step (Note 6)

TA= +25°C -5.0 +3.8

500 650

MAX2609

MAX2608, QL≥40

MAX2607, QL≥35

MAX2606, QL≥35

MAX2605, QL≥35

-107 dBc/Hz

-100

-93

-117

Phase Noise (Note 8)

-112

fOFFSET = 100kHz

-4.7 +3.6

TA= +25°C

PARAMETER MIN TYP MAX UNITS

Guaranteed Frequency Limits

(relative to nominal) (Note 5)

-4.1 +3.2

300 500

-4.4 +3.4

-4.6 +3.6

Oscillator Nominal Frequency

Range (Note 4)

45 70

70 150

150 300

CONDITIONS

MAX2606

MAX2605

MAX2608

MAX2607

MAX2608

MAX2605

MAX2606

MAX2607

Single-Ended Output Power

(Note 7) -10 dBm

TA= -40°C to +85°C

-2.25 +2.25

-2.5 +2.5

-2.75 +2.75

-2.8 +2.8

-3.0 +3.0

MAX2609

MHz

MAX2605–MAX2609

Maxim Integrated

45MHz to 650MHz, Integrated IF

VCOs with Differential Output

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)

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 ƒMIN and ƒMAX are measured at VTUNE = 0.4V and VTUNE = 2.4V, respectively. Passing

requirements are: ƒ ≤ƒMIN at VTUNE = 0.4 and ƒ ≥ƒMAX 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 50Ωload 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.

1.0

1.5

2.0

3.0

2.5

3.5

4.0

-40 0-20 20 40 60 80

SUPPLY CURRENT

vs. TEMPERATURE

MAX2605/9-01

TEMPERATURE (°C)

SUPPLY CURRENT (mA)

MAX2609

MAX2605

MAX2606MAX2607MAX2608

0.02

0.06

0.04

0.08

0.10

-40 0-20 20 40 60 80

TUNE INPUT LEAKAGE CURRENT

vs. TEMPERATURE

MAX2605/9-02

TEMPERATURE (°C)

LEAKAGE CURRENT (nA)

0 1.00.5 1.5 2.0 2.5 3.0

MAX2605

VCO TUNING CURVE

MAX2605/9-03

VTUNE (V)

FREQUENCY (MHz)

Typical Operating Characteristics

(MAX260_ EV kit, VCC = +2.75V, VTUNE = 1.4V, TA = +25°C, unless otherwise noted.)

dBcEven-Order Harmonics -30Differential, RL= 50Ωeach side

PARAMETER MIN TYP MAX UNITS

CONDITIONS

MAX2605

120

MAX2606

480

MAX2608

220

MAX2607

Supply Pushing (Note 9)

720

kHz/V

MAX2609

MAX2605–MAX2609

Maxim Integrated

45MHz to 650MHz, Integrated IF

VCOs with Differential Output

100

110

120

130

0 1.00.5 1.5 2.0 2.5 3.0

MAX2606

VCO TUNING CURVE

MAX2605/9-04

VTUNE (V)

FREQUENCY (MHz)

160

180

200

220

240

260

0 1.00.5 1.5 2.0 2.5 3.0

MAX2607

VCO TUNING CURVE

MAX2605/9-05

VTUNE (V)

FREQUENCY (MHz)

310

340

370

400

430

0 1.00.5 1.5 2.0 2.5 3.0

MAX2608

VCO TUNING CURVE

MAX2605/9-06

VTUNE (V)

FREQUENCY (MHz)

480

520

560

600

640

680

0 1.00.5 1.5 2.0 2.5 3.0

MAX2609

VCO TUNING CURVE

MAX2605/9-07

VTUNE (V)

FREQUENCY (MHz)

-50

-40

-30

-20

-10

4fo5fo

2fo3fo

fo6fo7fo

MAX2605/9-08

FREQUENCY

(dB)

OUTPUT SPECTRUM

NAME FUNCTION

1IND Tuning Inductor Port. Connect an inductor from IND to GND to set VCO center frequency (see Oscillation

Frequency).

2GND Ground. Connect to the ground plane with a low-inductance path.

3TUNE Voltage-Control Input for Frequency Tuning. Input voltage range from +0.4V to +2.4V.

4OUT- 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+.

6OUT+ 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.

Pin Description

Typical Operating Characteristics (continued)

(MAX260_ EV kit, VCC = +2.75V, VTUNE = 1.4V, TA = +25°C, unless otherwise noted.)

MAX2605–MAX2609

Maxim Integrated

45MHz to 650MHz, Integrated IF

VCOs with Differential Output

Detailed Description

The MAX2605–MAX2609 are low-noise VCOs designed

for fixed/single-frequency IF applications. The core

oscillator circuit is based on the well-known Colpitts

topology. The varactor and feedback capacitors are

integrated on-chip so that only an external inductor is

required to establish the frequency of oscillation and

produce a properly operating VCO. The tuning range,

biasing, startup, etc., are all managed within the IC. This

highly integrated design dramatically simplifies the

parts’ application.

The tuning range is wide enough so that, with the use

of ±2% tolerance inductors, no board-level adjustments

to the oscillation frequency are necessary. Once the

correct inductor value is chosen, the VCO is guaran-

teed always to tune to the desired operating frequency.

In addition, with the use of inductors of moderate Q (35

to 40), the VCO achieves excellent phase-noise perfor-

mance.

Applications Information

Desired Oscillation Frequency

The desired VCO operating frequency is set by the

value of the external inductance, LF. Figures 1–5 show

the inductance value LFrequired to achieve the desired

oscillation frequency. The inductor value can be taken

directly from these figures. Inductance must be select-

ed accurately to ensure proper operation over all con-

ditions.

Inductor Implementation

The inductance value required for the desired operat-

ing frequency may not necessarily coincide with a stan-

dard-value SMT inductor, which typically increases size

in ~1.2x steps. In such cases, the inductance must be

constructed from two inductors, LF1 and LF2, in order to

achieve the desired inductance value. Choose LF1 to

be a standard-value inductor with a value just less than

that required for LF. Choose LF2 to be a standard-value

inductor with a value just less than (LF- LF1). LF1

should adhere to the minimum Q requirements, but LF2

may be implemented as a lower-cost, lower-Q, thin-film

SMT inductor. Its lower Q has only a small impact on

the overall Q of the total inductance because it is <20%

of the total inductance. However, the overall Q of LF1

and LF2 must be greater than the minimum inductor Q

(Table 1).

It is also permissible to use PC board traces to provide

a small amount of inductance, thereby adjusting the

total inductance value. On the MAX2608/MAX2609, the

inductance values for LF2 are sometimes more exactly

implemented as a PC board trace (shorted to GND),

rather than an SMT inductor. When designing LF with

two inductors, use the simple model in Figure 7 to cal-

culate XLand LEQ.

The LFin Figures 1–5 represents an equivalent induc-

tance as seen by pin 1 (IND). The equivalent induc-

tance corresponds to the inductive reactance

connected to IND at the desired oscillation frequency

(fNOMINAL).

LEQ = XL/ (2πfNOMINAL) as seen in Figure 8

Design LEQ = LFat the desired fNOMINAL. The

MAX2605–MAX2609 are designed to tolerate approxi-

mately 0.5pF of external parasitic capacitance at IND.

This parasitic capacitance arises from the pad capaci-

tance at the device pin and pads for the inductor.

Additional shunt capacitance is not recommended

because it degrades the tuning range.

Bypass Capacitor on TUNE

The MAX2605–MAX2609’s oscillator design uses a vari-

ant of the Colpitts topology, where DC bias for the var-

actor is applied via a DC voltage on TUNE and a

ground connection through the external inductor LF.

TUNE must also have a high-frequency AC ground for

Table 1. External Inductor LFRange Table 2. CBYPASS Values

403.9 ≤LF≤15500 to 650MAX2609

MIN

INDUCTOR

10 ≤LF≤47300 to 500MAX2608

39 ≤LF≤180

150 ≤LF≤820

680 ≤LF≤2200

INDUCTANCE

RANGE

(nH)

FREQUENCY

RANGE

(MHz)

45 to 70

70 to 150

150 to 300MAX2607

MAX2606

MAX2605

PART

≥39 pFMAX2609

≥100 pFMAX2608

≥330 pF

≥680 pF

≥820 pF

CBYPASS

MAX2607

MAX2606

MAX2605

DEVICE

MAX2605–MAX2609

Maxim Integrated

45MHz to 650MHz, Integrated IF

VCOs with Differential Output

MAX2605

REQUIRED INDUCTANCE vs. DESIRED VCO FIXED FREQUENCY

1900

1800

1700

1600

1500

1400

1300

1200

1100

1000

900

800

700

REQUIRED INDUCTANCE (nH)

45 47 49 51 53 55 57 59 61 63 65 67 69

EFFECTIVE INDUCTANCE

FROM IND TO GND

INDUCTOR VALUE

MOUNTED ON EV KIT

MEASUREMENT CONDITIONS

VCC = 2.75V, TA = 25°C,

RLOAD = 100Ω||50Ω (100Ω RESISTIVE PULL-UP PARALLELED WITH 50Ω

VNA IMPEDANCE), UNUSED OUTPUT TERMINATED IN 50Ω,

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).

DESIRED VCO FIXED FREQUENCY (MHz)

Figure 1. MAX2605 Required Inductance vs. Desired VCO Fixed Frequency

MAX2605–MAX2609

Maxim Integrated

45MHz to 650MHz, Integrated IF

VCOs with Differential Output

MAX2606

REQUIRED INDUCTANCE vs. DESIRED VCO FIXED FREQUENCY

790

740

690

640

590

540

490

440

390

340

290

240

190

REQUIRED INDUCTANCE (nH)

75 80 85 90 95 100 105 110 115 120 125 130 135

EFFECTIVE INDUCTANCE

FROM IND TO GND

INDUCTOR VALUE

MOUNTED ON EV KIT

140

70 140 145 150

MEASUREMENT CONDITIONS

VCC = 2.75V, TA = 25°C,

RLOAD = 100Ω||50Ω (100Ω RESISTIVE PULL-UP PARALLELED WITH 50Ω

VNA IMPEDANCE), UNUSED OUTPUT TERMINATED IN 50Ω,

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).

DESIRED VCO FIXED FREQUENCY (MHz)

Figure 2. MAX2606 Required Inductance vs. Desired VCO Fixed Frequency

MAX2605–MAX2609

Maxim Integrated

45MHz to 650MHz, Integrated IF

VCOs with Differential Output

MAX2607

REQUIRED INDUCTANCE vs. DESIRED VCO FIXED FREQUENCY

160

150

140

130

120

110

100

REQUIRED INDUCTANCE (nH)

160 170 180 190 200 210 220 230 240 250 260 270 280

INDUCTOR VALUE

MOUNTED ON EV KIT

150 290 300

170

EFFECTIVE INDUCTANCE

FROM IND TO GND

MEASUREMENT CONDITIONS

VCC = 2.75V, TA = 25°C,

RLOAD = 100Ω||50Ω (100Ω RESISTIVE PULL-UP PARALLELED WITH 50Ω

VNA IMPEDANCE), UNUSED OUTPUT TERMINATED IN 50Ω,

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).

DESIRED VCO FIXED FREQUENCY (MHz)

Figure 3. MAX2607 Required Inductance vs. Desired VCO Fixed Frequency

MAX2605–MAX2609

Maxim Integrated

45MHz to 650MHz, Integrated IF

VCOs with Differential Output

MAX2608

REQUIRED INDUCTANCE vs. DESIRED VCO FIXED FREQUENCY

40.0

38.0

37.0

32.0

29.0

27.0

25.0

22.0

20.0

17.0

15.0

13.0

11.0

REQUIRED INDUCTANCE (nH)

310 320 330 340 350 360 370 380 390 400 410 420 470

9.0

300 480

41.0

420 430 440 450 460 490 500

36.0

35.0

34.0

33.0

31.0

30.0

28.0

26.0

24.0

23.0

21.0

19.0

18.0

16.0

14.0

12.0

10.0

EFFECTIVE INDUCTANCE

FROM IND TO GND

INDUCTOR VALUE

MOUNTED ON EV KIT

MEASUREMENT CONDITIONS

VCC = 2.75V, TA = 25°C,

RLOAD = 100Ω||50Ω (100Ω RESISTIVE PULL-UP PARALLELED WITH 50Ω

VNA IMPEDANCE), UNUSED OUTPUT TERMINATED IN 50Ω,

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).

Figure 4. MAX2608 Required Inductance vs. Desired VCO Fixed Frequency

MAX2605–MAX2609

Maxim Integrated

45MHz to 650MHz, Integrated IF

VCOs with Differential Output

MAX2609

REQUIRED INDUCTANCE vs. DESIRED VCO FIXED FREQUENCY

13.5

13.0

11.5

11.0

10.0

9.5

9.0

8.5

7.5

6.5

6.0

5.5

5.0

REQUIRED INDUCTANCE (nH)

510 520 530 540 550 560 570 580 590 600 610 620 630

3.5

500 640 650

14.0

EFFECTIVE INDUCTANCE

FROM IND TO GND

INDUCTOR VALUE

MOUNTED ON EV KIT

12.5

12.0

10.5

8.0

7.0

4.5

4.0

DESIRED VCO FIXED FREQUENCY (MHz)

MEASUREMENT CONDITIONS

VCC = 2.75V, TA = 25°C,

RLOAD = 100Ω||50Ω (100Ω RESISTIVE PULL-UP PARALLELED WITH 50Ω

VNA IMPEDANCE), UNUSED OUTPUT TERMINATED IN 50Ω,

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).

Figure 5. MAX2609 Required Inductance vs. Desired VCO Fixed Frequency

MAX2605–MAX2609

Maxim Integrated

45MHz to 650MHz, Integrated IF

VCOs with Differential Output

the cathode of the varactor. This is accomplished

through the use of a simple bypass capacitor connect-

ed from TUNE to ground. The value of this capacitor

should be greater than or equal to the values listed in

Table 2.

This capacitor provides an AC “short” to ground for the

internal node of the varactor. It is acceptable to select

the next-largest standard-value capacitor. Use a

capacitor with a low-loss dielectric such as NPO; X7R-

based capacitors are not suitable. Omitting this capac-

itor would affect the tuning characteristics of the

MAX2605–MAX2609. Proper operation of the VCOs

requires the use of this bypass capacitor.

The MAX2605–MAX2609 VCO is designed to tune over

the full tuning range with a voltage range of 0.4V to

2.4V applied to TUNE. This voltage typically originates

from the output of the phase-locked (PLL) loop filter.

Output Interface

The MAX2605–MAX2609 VCO includes a differential

output amplifier after the oscillator core. The amplifier

stage provides valuable isolation and offers a flexible

interface to the IF stages, such as a mixer and PLL

prescaler. The output can be taken single ended or dif-

ferentially; however, the maximum output power and

lowest harmonic output are achieved in the differential

output mode.

Both outputs (OUT- and OUT+) are open-collector

types and require a pull-up element to VCC; this can be

either resistive or inductive. A resistor pull-up is the

most straightforward method of interfacing to the out-

put, and works well in applications that operate at lower

frequencies or only require a modest voltage swing.

In Figure 6, Z1 and Z2 are 1kΩpull-up resistors that are

connected from OUT+ and OUT- to VCC, respectively.

These resistors provide DC bias for the output amplifier

and are the maximum value permitted with compliance

to the output voltage swing limits. In addition, the 1kΩ

resistors maximize the swing at the load. DC-blocking

capacitors are connected from OUT- and OUT+ to the

load. If the load driven is primarily resistive and the

VCO operating frequency is below the -3dB bandwidth

of the output network, then the peak-to-peak differential

signal amplitude is approximately:

To optimize the output voltage swing or the output

power, use a reactive power match. The matching net-

work is a simple shunt-inductor series-capacitor circuit,

as shown in Figure 6. The inductors are connected

from OUT- and OUT+ (in place of resistors) to VCC to

provide DC bias for the output stage. The series capac-

itors are connected from OUT- and OUT+ to the load.

The values for LMATCH (Z1and Z2) and CMATCH (C1

and C2) are chosen according to the operating fre-

quency and load impedance. As the output stage is

essentially a high-speed current switch, traditional lin-

ear impedance using techniques with [S] parameters

do not apply. To achieve a reactive power match, start

with the component values provided in the EV kit, and

adjust values experimentally.

In general, the differential output may be applied in any

manner, as would conventional differential outputs. The

only constraints are the need for a pull-up element to

VCC and a voltage swing limit at the output pins OUT-

and OUT+.

Layout Considerations

In general, a properly designed PC board is essential

to any RF/microwave circuit or system. Always use con-

trolled impedance lines (microstrip, coplanar wave-

guide, etc.) on high-frequency signals. Always place

decoupling capacitors as close to the VCC pin as pos-

sible. For low phase noise and spurious content, use an

appropriate size decoupling capacitor. For long VCC

lines, it may be necessary to add additional decoupling

capacitors located further from the device. Always pro-

vide a low-inductance path to ground. Keep the GND

vias as close to the device as possible. In addition, the

VCO should be placed as far away from the noisy sec-

tion of a larger system, such as a switching regulator or

digital circuits. Use star topology to separate the

ground returns.

The resonator tank circuit (LF) is critical in determining

the VCO’s performance. For best performance, use

high-Q components and choose values carefully. To

minimize the effects of parasitic elements, which

degrade circuit performance, place LFand CBYP close

to their respective pins. Specifically, place CBYP direct-

ly across pins 2 (GND) and 3 (TUNE).

For the higher frequency versions, consider the extra

parasitic inductance and capacitance when determin-

ing the oscillation frequency. Be sure to account for the

following: PC board pad capacitance at IND, PC board

pad capacitance at the junction of two series inductors,

series inductance of any PC board traces, and the

inductance in the ground return path from the ground-

ed side of the inductor and IC’s GND pin. For best

results, connect the “ground” side to the tuning induc-

tor as close to pin 2 as possible. In addition, remove

the ground plane around and under LFand CBYP to

minimize the effects of parasitic capacitance.

V diff 2 1mA 1k R

1k R

OUTp p LOAD

LOAD

−

()

=× ×













Ω

MAX2605–MAX2609

Maxim Integrated

45MHz to 650MHz, Integrated IF

VCOs with Differential Output

Chip Information

TRANSISTOR COUNT: 158

RLOAD

OUT-

TUNE

FROM PLL LOOP

FILTER OUTPUT

OUT+

VCC

CBYP

MAX2605

MAX2606

MAX2607

MAX2608

MAX2609

VCC

Figure 6. Typical Operating Circuit

MAX2605–MAX2609

Maxim Integrated

45MHz to 650MHz, Integrated IF

VCOs with Differential Output

IND

MAX2605

MAX2606

MAX2607

MAX2608

MAX2609

LF2 CPAR1

LF1

CPAR2

Figure 7. Simple Model of External Inductance

IND

MAX2605

MAX2606

MAX2607

MAX2608

MAX2609

LEQ = XL / 2π ƒNOMINAL

Figure 8. Inductive Reactance at Pin 1 (IND)

MAX2605

MAX2606

MAX2607

MAX2608

MAX2609 4

VCC

Figure 9. Output Matching Network

MAX2605–MAX2609

Maxim Integrated

Package Information

6LSOT.EPS

45MHz to 650MHz, Integrated IF

VCOs with Differential Output

Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.

Maxim reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical

Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.

MAX2605–MAX2609

Mouser Electronics

Authorized Distributor

Click to View Pricing, Inventory, Delivery & Lifecycle Information:

Maxim Integrated:

MAX2607EUT+T MAX2605EUT+T MAX2606EUT+T MAX2608EUT+T MAX2609EUT+T MAX2605EUT-T

MAX2606EUT-T MAX2607EUT-T MAX2608EUT-T MAX2609EUT-T MAX2608EUT+