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19-1673; Rev 0a; 4/02
ANUAL N KIT M LUATIO ABLE EVA AVAIL
45MHz to 650MHz, Integrated IF VCOs with Differential Output
Features
o Small Size o Integrated Varactor for Tuning o Low Phase Noise o Wide Application Frequency Range o Differential or Single-Ended Outputs o Single +2.7V to +5.5V Supply o Ultra-Small SOT23-6 Package o On-Chip Temperature-Stable Bias o Low-Current Operation
General Description
The MAX2605MAX2609 are compact, high-performance intermediate-frequency (IF) voltage-controlled oscillators (VCOs) designed specifically for demanding portable wireless communication systems. They combine monolithic 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 MAX2605MAX2609 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 driving 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 MAX2605MAX2609 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.
MAX2605MAX2609
Ordering Information
PART TEMP. RANGE -40°C to +85°C -40°C to +85°C -40°C to +85°C -40°C to +85°C -40°C to +85°C PINPACKAGE 6 SOT23-6 6 SOT23-6 6 SOT23-6 6 SOT23-6 6 SOT23-6 TOP MARK AABB AABC AABD AABE AABF
Applications
Cellular and PCS Mobile Phones 2.4GHz ISM Band 902MHz to 928MHz ISM Band Land Mobile Radio GPS Receivers General-Purpose IF Oscillators
MAX2605EUT-T MAX2606EUT-T MAX2607EUT-T MAX2608EUT-T MAX2609EUT-T
Selector Guide
PART MAX2605 MAX2606 MAX2607 MAX2608 MAX2609 FREQUENCY RANGE (MHz) 45 to 70 70 to 150 150 to 300 300 to 500 500 to 650 SUPPLY CURRENT (mA) 1.9 2.1 2.1 2.7 3.6 PHASE NOISE (dBc/Hz) -117 -112 -107 -100 -93
IND 1
Pin Configuration/ Functional Diagram
TOP VIEW
GND 2
MAX2605 MAX2606 MAX2607 MAX2608 MAX2609
6
OUT+
5
VCC
TUNE 3
4
OUT-
SOT23-6
________________________________________________________________ Maxim Integrated Products
1
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45MHz to 650MHz, Integrated IF VCOs with Differential Output MAX2605MAX2609
ABSOLUTE MAXIMUM RATINGS
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
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 Supply Voltage MAX2605 MAX2606 Supply Current (Note 2) MAX2607 MAX2608 MAX2609 DC Output Current (Note 3) TUNE Input Current OUT+ plus OUTTA = +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 TA = -40°C to +85°C TA = +25°C TA = -40°C to +85°C 0.5 1.0 0.03 3.6 2.7 2.1 2.1 CONDITIONS MIN 2.7 1.9 TYP MAX 5.5 2.6 2.8 2.7 3.0 3.2 3.5 4.4 5.5 6.8 7.5 1.5 mA nA mA UNITS V
2
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45MHz to 650MHz, Integrated IF VCOs with Differential Output
AC ELECTRICAL CHARACTERISTICS
(MAX2605MAX2609 EV kits, 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.) (Note 1) PARAMETER MAX2605 MAX2606 Oscillator Nominal Frequency Range (Note 4) MAX2607 MAX2608 MAX2609 MAX2605 MAX2606 Guaranteed Frequency Limits (relative to nominal) (Note 5) MAX2607 MAX2608 MAX2609 Peak Tuning Gain Single-Ended Output Power (Note 7) MAX2605, QL 35 MAX2606, QL 35 Phase Noise (Note 8) fOFFSET = 100kHz MAX2607, QL 35 MAX2608, QL 40 MAX2609, QL 40 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 TA = -40°C to +85°C TA = +25°C TA = -40°C to +85°C CONDITIONS MIN 45 70 150 300 500 -4.1 -2.25 -4.4 -2.5 -4.6 -2.75 -4.7 -2.8 -5.0 -3.0 14.5 -10 -117 -112 -107 -100 -93 dBc/Hz TYP MAX 70 150 300 500 650 +3.2 +2.25 +3.4 +2.5 +3.6 +2.75 +3.6 +2.8 +3.8 +3.0 %/V dBm % MHz UNITS
MAX2605MAX2609
VTUNE = 0.4V to 0.6V step (Note 6)
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3
45MHz to 650MHz, Integrated IF VCOs with Differential Output MAX2605MAX2609
AC ELECTRICAL CHARACTERISTICS (continued)
(MAX2605MAX2609 EV kits, 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.) (Note 1) PARAMETER Even-Order Harmonics MAX2605 MAX2606 Supply Pushing (Note 9) MAX2607 MAX2608 MAX2609 CONDITIONS Differential, RL = 50 each side MIN TYP -30 60 120 220 480 720 kHz/V MAX UNITS dBc
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 internal 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 MAX2605MAX2609. 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 vs. TEMPERATURE
MAX2605/9-01
TUNE INPUT LEAKAGE CURRENT vs. TEMPERATURE
MAX2605/9-02
MAX2605 VCO TUNING CURVE
MAX2605/9-03
4.0 3.5 SUPPLY CURRENT (mA) MAX2609 3.0 2.5 2.0 1.5 1.0 -40 -20 0 20 40 60 80 TEMPERATURE (°C) MAX2608 MAX2607 MAX2606
0.10
65
0.08 LEAKAGE CURRENT (nA)
60 FREQUENCY (MHz)
0.06
55
0.04
50 0.02
MAX2605 0 -40 -20 0 20 40 60 80 TEMPERATURE (°C) 45 0 0.5 1.0 1.5 VTUNE (V) 2.0 2.5 3.0
4
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45MHz to 650MHz, Integrated IF VCOs with Differential Output MAX2605MAX2609
Typical Operating Characteristics (continued)
(MAX260_ EV kit, VCC = +2.75V, VTUNE = 1.4V, TA = +25°C, unless otherwise noted.)
MAX2606 VCO TUNING CURVE
MAX2605/9-04
MAX2607 VCO TUNING CURVE
MAX2605/9-05
MAX2608 VCO TUNING CURVE
MAX2605/9-06
130
260
430
240 FREQUENCY (MHz)
120 FREQUENCY (MHz) 220 FREQUENCY (MHz) 0 0.5 1.0 1.5 VTUNE (V) 2.0 2.5 3.0
400
110
370
200
100
180
340
90 0 0.5 1.0 1.5 VTUNE (V) 2.0 2.5 3.0
160
310 0 0.5 1.0 1.5 VTUNE (V) 2.0 2.5 3.0
MAX2609 VCO TUNING CURVE
MAX2605/9-07
OUTPUT SPECTRUM
MAX2605/9-08
680
0
640 FREQUENCY (MHz)
-10
600 (dB) 560
-20
-30
520
-40
480 0 0.5 1.0 1.5 VTUNE (V) 2.0 2.5 3.0
-50 fo 2fo 3fo 4fo 5fo 6fo 7fo FREQUENCY
Pin Description
PIN 1 2 3 4 NAME IND GND TUNE OUTFUNCTION Tuning Inductor Port. Connect an inductor from IND to GND to set VCO center frequency (see Oscillation Frequency). Ground. Connect to the ground plane with a low-inductance path. Voltage-Control Input for Frequency Tuning. Input voltage range from +0.4V to +2.4V. 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+. Supply Voltage Connection. Connect an external bypass capacitor to ground for low noise and low spurious-output content. See Layout Issues for more details. 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
6
OUT+
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5
45MHz to 650MHz, Integrated IF VCOs with Differential Output MAX2605MAX2609
Detailed Description
The MAX2605MAX2609 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 guaranteed 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 performance. that required for LF. Choose LF2 to be a standard-value inductor with a value just less than (LF - L F1 ). L F1 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 calculate XL and LEQ. The LF in Figures 15 represents an equivalent inductance as seen by pin 1 (IND). The equivalent inductance corresponds to the inductive reactance connected to IND at the desired oscillation frequency (fNOMINAL). LEQ = XL / (2 fNOMINAL) as seen in Figure 8 Design L EQ = L F at the desired f NOMINAL . The MAX2605MAX2609 are designed to tolerate approximately 0.5pF of external parasitic capacitance at IND. This parasitic capacitance arises from the pad capacitance at the device pin and pads for the inductor. Additional shunt capacitance is not recommended because it degrades the tuning range.
Applications Information
Desired Oscillation Frequency
The desired VCO operating frequency is set by the value of the external inductance, LF. Figures 15 show the inductance value LF required to achieve the desired oscillation frequency. The inductor value can be taken directly from these figures. Inductance must be selected accurately to ensure proper operation over all conditions.
Inductor Implementation
The inductance value required for the desired operating frequency may not necessarily coincide with a standard-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
Bypass Capacitor on TUNE
The MAX2605MAX2609's oscillator design uses a variant of the Colpitts topology, where DC bias for the varactor 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 LF Range
PART MAX2605 MAX2606 MAX2607 MAX2608 MAX2609 6 FREQUENCY RANGE (MHz) 45 to 70 70 to 150 150 to 300 300 to 500 500 to 650 INDUCTANCE RANGE (nH) 680 LF 2200 150 LF 820 39 LF 180 10 LF 47 3.9 LF 15 MIN INDUCTOR Q 35 35 35 40 40
Table 2. CBYPASS Values
DEVICE MAX2605 MAX2606 MAX2607 MAX2608 MAX2609 CBYPASS 820 pF 680 pF 330 pF 100 pF 39 pF
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45MHz to 650MHz, Integrated IF VCOs with Differential Output MAX2605MAX2609
MAX2605 REQUIRED INDUCTANCE vs. DESIRED VCO FIXED FREQUENCY
1900
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).
1800
1700
1600
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 MAX2605MAX2609
MAX2606 REQUIRED INDUCTANCE vs. DESIRED VCO FIXED FREQUENCY
790 740 690 640
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).
590
REQUIRED INDUCTANCE (nH)
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 MAX2605MAX2609
MAX2607 REQUIRED INDUCTANCE vs. DESIRED VCO FIXED FREQUENCY
170 160 150 140 130
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).
120 REQUIRED INDUCTANCE (nH) 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 MAX2605MAX2609
41.0 40.0 38.0 37.0 36.0 35.0 34.0 33.0 32.0 31.0 30.0 29.0 28.0 27.0 26.0 25.0 24.0 23.0 22.0 21.0 20.0 19.0 18.0 17.0 16.0 15.0 14.0 13.0 12.0 11.0
MAX2608 REQUIRED INDUCTANCE vs. DESIRED VCO FIXED FREQUENCY
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).
REQUIRED INDUCTANCE (nH)
EFFECTIVE INDUCTANCE FROM IND TO GND
INDUCTOR VALUE MOUNTED ON EV KIT
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 MAX2605MAX2609
MAX2609 REQUIRED INDUCTANCE vs. DESIRED VCO FIXED FREQUENCY
14.0 13.5 13.0 12.5 12.0 11.5 11.0 10.5 REQUIRED INDUCTANCE (nH) 10.0 9.5 9.0 8.5 8.0 7.5 7.0 6.5 6.0 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 INDUCTOR VALUE MOUNTED ON EV KIT EFFECTIVE INDUCTANCE FROM IND TO GND
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).
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 MAX2605MAX2609
the cathode of the varactor. This is accomplished through the use of a simple bypass capacitor connected 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; X7Rbased capacitors are not suitable. Omitting this capacitor would affect the tuning characteristics of the MAX2605MAX2609. Proper operation of the VCOs requires the use of this bypass capacitor. The MAX2605MAX2609 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. from OUT- and OUT+ (in place of resistors) to VCC to provide DC bias for the output stage. The series capacitors are connected from OUT- and OUT+ to the load. The values for LMATCH (Z1 and Z2) and CMATCH (C1 and C2) are chosen according to the operating frequency and load impedance. As the output stage is essentially a high-speed current switch, traditional linear 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 OUTand OUT+.
Layout Considerations
In general, a properly designed PC board is essential to any RF/microwave circuit or system. Always use controlled impedance lines (microstrip, coplanar waveguide, etc.) on high-frequency signals. Always place decoupling capacitors as close to the VCC pin as possible. 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 provide 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 section 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 LF and CBYP close to their respective pins. Specifically, place CBYP directly across pins 2 (GND) and 3 (TUNE). For the higher frequency versions, consider the extra parasitic inductance and capacitance when determining 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 grounded side of the inductor and IC's GND pin. For best results, connect the "ground" side to the tuning inductor as close to pin 2 as possible. In addition, remove the ground plane around and under LF and CBYP to minimize the effects of parasitic capacitance.
Output Interface
The MAX2605MAX2609 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 differentially; 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 output, and works well in applications that operate at lower frequencies or only require a modest voltage swing. In Figure 6, Z1 and Z2 are 1k pull-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 1k 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:
1k × R LOAD VOUTp -p diff = 2 × 1mA 1k + R LOAD
( )
To optimize the output voltage swing or the output power, use a reactive power match. The matching network is a simple shunt-inductor series-capacitor circuit, as shown in Figure 6. The inductors are connected
12
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45MHz to 650MHz, Integrated IF VCOs with Differential Output MAX2605MAX2609
VCC C1 1 6 OUT+ Z1 C3 5 VCC Z2 C2 TUNE FROM PLL LOOP FILTER OUTPUT 3 4 OUTRLOAD RLOAD
LF 2 CBYP
MAX2605 MAX2606 MAX2607 MAX2608 MAX2609
Figure 6. Typical Operating Circuit
Chip Information
TRANSISTOR COUNT: 158
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13
45MHz to 650MHz, Integrated IF VCOs with Differential Output MAX2605MAX2609
LEQ = XL / 2 NOMINAL LF1 IND 1 IND
CPAR2
LF2
CPAR1
MAX2605 MAX2606 MAX2607 MAX2608 MAX2609
1
XL
MAX2605 MAX2606 MAX2607 MAX2608 MAX2609
Figure 7. Simple Model of External Inductance
Figure 8. Inductive Reactance at Pin 1 (IND)
VCC
MAX2605 MAX2606 MAX2607 MAX2608 MAX2609
4
ZL
Figure 9. Output Matching Network
14
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45MHz to 650MHz, Integrated IF VCOs with Differential Output
Package Information
6LSOT.EPS
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