19-1673; Rev 0a; 4/02 L MANUA ION KIT T A U L EVA BLE AVAILA 45MHz to 650MHz, Integrated IF VCOs with Differential Output Features The MAX2605–MAX2609 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. ♦ Small Size 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 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 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. ♦ Differential or Single-Ended Outputs Applications Cellular and PCS Mobile Phones ♦ Integrated Varactor for Tuning ♦ Low Phase Noise ♦ Wide Application Frequency Range ♦ Single +2.7V to +5.5V Supply ♦ Ultra-Small SOT23-6 Package ♦ On-Chip Temperature-Stable Bias ♦ Low-Current Operation Ordering Information PART TEMP. RANGE PINPACKAGE TOP MARK MAX2605EUT-T -40°C to +85°C 6 SOT23-6 AABB MAX2606EUT-T -40°C to +85°C 6 SOT23-6 AABC MAX2607EUT-T -40°C to +85°C 6 SOT23-6 AABD 2.4GHz ISM Band MAX2608EUT-T -40°C to +85°C 6 SOT23-6 AABE 902MHz to 928MHz ISM Band MAX2609EUT-T -40°C to +85°C 6 SOT23-6 AABF Land Mobile Radio GPS Receivers General-Purpose IF Oscillators Pin Configuration/ Functional Diagram Selector Guide FREQUENCY RANGE (MHz) SUPPLY CURRENT (mA) PHASE NOISE (dBc/Hz) MAX2605 45 to 70 1.9 -117 MAX2606 MAX2607 MAX2608 MAX2609 70 to 150 150 to 300 300 to 500 500 to 650 2.1 2.1 2.7 3.6 -112 -107 -100 -93 PART TOP VIEW IND 1 GND 2 MAX2605 MAX2606 MAX2607 MAX2608 MAX2609 TUNE 3 6 OUT+ 5 VCC 4 OUT- SOT23-6 ________________________________________________________________ Maxim Integrated Products 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. 1 MAX2605–MAX2609 General Description MAX2605–MAX2609 45MHz to 650MHz, Integrated IF VCOs with Differential Output 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 CONDITIONS Supply Voltage MAX2606 MAX2607 MAX2608 MAX2609 DC Output Current (Note 3) TUNE Input Current 2 TYP MAX 1.9 2.6 2.7 MAX2605 Supply Current (Note 2) MIN OUT+ plus OUT- TA = +25°C 5.5 TA = -40°C to +85°C UNITS V 2.8 TA = +25°C 2.1 2.7 2.1 3.2 TA = -40°C to +85°C 3.0 TA = +25°C TA = -40°C to +85°C 3.5 TA = +25°C 2.7 4.4 3.6 6.8 TA = -40°C to +85°C mA 5.5 TA = +25°C TA = -40°C to +85°C 7.5 0.5 1.0 0.03 _______________________________________________________________________________________ 1.5 mA nA 45MHz to 650MHz, Integrated IF VCOs with Differential Output (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 values are at VCC = +2.75V, VTUNE = 1.5V, and TA = +25°C.) (Note 1) PARAMETER Oscillator Nominal Frequency Range (Note 4) CONDITIONS 45 70 70 150 MAX2607 150 300 MAX2608 300 500 MAX2609 500 650 TA = +25°C -4.1 +3.2 TA = -40°C to +85°C -2.25 +2.25 TA = +25°C -4.4 +3.4 TA = -40°C to +85°C -2.5 +2.5 TA = +25°C -4.6 +3.6 TA = -40°C to +85°C -2.75 +2.75 TA = +25°C -4.7 +3.6 TA = -40°C to +85°C -2.8 +2.8 TA = +25°C -5.0 +3.8 TA = -40°C to +85°C -3.0 MAX2607 MAX2608 MAX2609 VTUNE = 0.4V to 0.6V step (Note 6) Single-Ended Output Power (Note 7) Phase Noise (Note 8) MAX MAX2605 MAX2606 Peak Tuning Gain TYP MAX2606 MAX2605 Guaranteed Frequency Limits (relative to nominal) (Note 5) MIN fOFFSET = 100kHz UNITS MHz % +3.0 14.5 %/V -10 dBm MAX2605, QL ≥ 35 -117 MAX2606, QL ≥ 35 -112 MAX2607, QL ≥ 35 -107 MAX2608, QL ≥ 40 -100 MAX2609, QL ≥ 40 -93 dBc/Hz _______________________________________________________________________________________ 3 MAX2605–MAX2609 AC ELECTRICAL CHARACTERISTICS 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 values are at VCC = +2.75V, VTUNE = 1.5V, and TA = +25°C.) (Note 1) PARAMETER CONDITIONS Even-Order Harmonics Supply Pushing (Note 9) MIN TYP Differential, RL = 50Ω each side -30 MAX2605 60 MAX2606 120 MAX2607 220 MAX2608 480 MAX2609 720 MAX UNITS dBc kHz/V 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 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 50Ω 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 vs. TEMPERATURE MAX2606 2.5 2.0 MAX2605/9-03 MAX2605/9-02 65 60 FREQUENCY (MHz) MAX2608 MAX2607 0.08 LEAKAGE CURRENT (nA) MAX2609 0.06 0.04 55 50 0.02 1.5 MAX2605 1.0 45 0 -40 -20 0 20 40 TEMPERATURE (°C) 4 0.10 MAX2605/9-01 3.5 3.0 MAX2605 VCO TUNING CURVE TUNE INPUT LEAKAGE CURRENT vs. TEMPERATURE 4.0 SUPPLY CURRENT (mA) MAX2605–MAX2609 45MHz to 650MHz, Integrated IF VCOs with Differential Output 60 80 -40 -20 0 20 40 TEMPERATURE (°C) 60 80 0 0.5 1.0 1.5 VTUNE (V) _______________________________________________________________________________________ 2.0 2.5 3.0 45MHz to 650MHz, Integrated IF VCOs with Differential Output MAX2607 VCO TUNING CURVE 430 MAX2605/9-05 260 MAX2605/9-04 130 MAX2608 VCO TUNING CURVE 240 110 100 FREQUENCY (MHz) FREQUENCY (MHz) 400 220 200 160 90 0 0.5 1.0 1.5 2.0 2.5 310 0 3.0 370 340 180 0.5 1.0 1.5 2.0 2.5 3.0 0 0.5 1.0 VTUNE (V) VTUNE (V) 1.5 2.0 2.5 3.0 VTUNE (V) MAX2609 VCO TUNING CURVE OUTPUT SPECTRUM 640 MAX2605/9-08 0 MAX2605/9-07 680 -10 600 -20 (dB) FREQUENCY (MHz) FREQUENCY (MHz) 120 MAX2605/9-06 MAX2606 VCO TUNING CURVE 560 -30 520 -40 -50 480 0 0.5 1.0 1.5 2.0 2.5 3.0 fo 2fo VTUNE (V) 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 spurious-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 MAX2605–MAX2609 Typical Operating Characteristics (continued) (MAX260_ EV kit, VCC = +2.75V, VTUNE = 1.4V, TA = +25°C, unless otherwise noted.) MAX2605–MAX2609 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 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. 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 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. 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 1–5 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 / (2π fNOMINAL) as seen in Figure 8 Inductor Implementation Design L EQ = L F at the desired f NOMINAL . The MAX2605–MAX2609 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. 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 The MAX2605–MAX2609’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 Table 2. CBYPASS Values FREQUENCY RANGE (MHz) INDUCTANCE RANGE (nH) MIN INDUCTOR Q DEVICE CBYPASS MAX2605 45 to 70 680 ≤ LF ≤ 2200 35 MAX2605 ≥ 820 pF MAX2606 70 to 150 150 ≤ LF ≤ 820 35 MAX2606 ≥ 680 pF MAX2607 150 to 300 39 ≤ LF ≤ 180 35 MAX2607 ≥ 330 pF MAX2608 300 to 500 10 ≤ LF ≤ 47 40 MAX2608 ≥ 100 pF MAX2609 500 to 650 3.9 ≤ LF ≤ 15 40 MAX2609 ≥ 39 pF PART 6 Bypass Capacitor on TUNE _______________________________________________________________________________________ 45MHz to 650MHz, Integrated IF VCOs with Differential Output MAX2605–MAX2609 MAX2605 REQUIRED INDUCTANCE vs. DESIRED VCO FIXED FREQUENCY 1900 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 1800 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). 1700 1600 REQUIRED INDUCTANCE (nH) 1500 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 MAX2605–MAX2609 45MHz to 650MHz, Integrated IF VCOs with Differential Output MAX2606 REQUIRED INDUCTANCE vs. DESIRED VCO FIXED FREQUENCY 790 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 740 690 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 VALUES (±2% INDUCTOR AND IC PROCESS VARIATION). 640 REQUIRED INDUCTANCE (nH) 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 MAX2605–MAX2609 MAX2607 REQUIRED INDUCTANCE vs. DESIRED VCO FIXED FREQUENCY 170 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 160 150 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). 140 130 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 MAX2605–MAX2609 45MHz to 650MHz, Integrated IF VCOs with Differential Output 41.0 40.0 38.0 37.0 36.0 35.0 REQUIRED INDUCTANCE (nH) 34.0 33.0 32.0 31.0 30.0 29.0 28.0 27.0 MAX2608 REQUIRED INDUCTANCE vs. DESIRED VCO FIXED FREQUENCY 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). 26.0 25.0 24.0 23.0 22.0 EFFECTIVE INDUCTANCE FROM IND TO GND 21.0 20.0 19.0 18.0 17.0 16.0 15.0 14.0 INDUCTOR VALUE 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 MAX2605–MAX2609 MAX2609 REQUIRED INDUCTANCE vs. DESIRED VCO FIXED FREQUENCY 14.0 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 13.5 13.0 12.5 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). 12.0 11.5 11.0 REQUIRED INDUCTANCE (nH) 10.5 EFFECTIVE INDUCTANCE FROM IND TO GND 10.0 9.5 9.0 8.5 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 MAX2605–MAX2609 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 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 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. 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+. Output Interface 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. 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 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 1kΩ 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 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: 1kΩ × R LOAD VOUTp −p diff = 2 × 1mA 1kΩ + 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 Layout Considerations ______________________________________________________________________________________ 45MHz to 650MHz, Integrated IF VCOs with Differential Output MAX2605–MAX2609 VCC C1 1 LF 2 MAX2605 MAX2606 MAX2607 MAX2608 MAX2609 6 OUT+ RLOAD Z1 C3 5 VCC CBYP Z2 RLOAD C2 3 TUNE 4 OUT- FROM PLL LOOP FILTER OUTPUT Figure 6. Typical Operating Circuit Chip Information TRANSISTOR COUNT: 158 ______________________________________________________________________________________ 13 MAX2605–MAX2609 45MHz to 650MHz, Integrated IF VCOs with Differential Output LEQ = XL / 2π ƒNOMINAL IND LF1 1 CPAR2 LF2 CPAR1 IND MAX2605 MAX2606 MAX2607 MAX2608 MAX2609 1 XL MAX2605 MAX2606 MAX2607 MAX2608 MAX2609 Figure 8. Inductive Reactance at Pin 1 (IND) Figure 7. Simple Model of External Inductance VCC MAX2605 MAX2606 MAX2607 MAX2608 MAX2609 4 Γ ZL Figure 9. Output Matching Network 14 ______________________________________________________________________________________ 45MHz to 650MHz, Integrated IF VCOs with Differential Output 6LSOT.EPS Package Information 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. 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