19-1350 Rev 2; 2/99 L MANUA ION KIT HEET T A U L EVA TA S WS DA FOLLO 900MHz Image-Reject Receivers with Transmit Mixer ____________________________Features ♦ Receive Mixer with 35dB Image Rejection ________________________Applications Cordless Phones Wireless Telemetry ♦ Adjustable-Gain LNA ♦ Up to +2dBm Combined Receiver Input IP3 ♦ 4dB Combined Receiver Noise Figure ♦ Optimized for Common Receiver IF Frequencies: 10.7MHz (MAX2424) 70MHz (MAX2426) ♦ PA Predriver Provides up to 0dBm ♦ Low Current Consumption: 23mA Receive 20mA Transmit 9.5mA Oscillator ♦ 0.5µA Shutdown Mode ♦ Operates from Single +2.7V to +4.8V Supply _______________Ordering Information PART TEMP. RANGE PIN-PACKAGE MAX2424EAI -40°C to +85°C 28 SSOP MAX2426EAI -40°C to +85°C 28 SSOP ___________________Pin Configuration TOP VIEW VCC 1 28 GND CAP1 2 27 GND RXOUT 3 26 GND GND 4 25 TANK RXIN 5 Wireless Networks VCC 6 MAX2424 MAX2426 24 TANK 23 VCC Spread-Spectrum Communications GND 7 Two-Way Paging GND 8 21 PREOUT TXOUT 9 20 PREGND Functional Diagram appears at end of data sheet. 22 VCC LNAGAIN 10 19 MOD VCC 11 18 DIV1 TXIN 12 17 VCOON TXIN 13 16 RXON CAP2 14 15 TXON SSOP ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 1-800-835-8769. MAX2424/MAX2426 ________________General Description The MAX2424/MAX2426 highly integrated front-end ICs provide the lowest cost solution for cordless and ISMband radios operating in the 900MHz band. Both devices incorporate a receive image-reject mixer (to reduce filter cost) as well as a versatile transmit mixer. The devices operate from a +2.7V to +4.8V single power supply, allowing direct connection to a 3-cell battery stack. The receive path incorporates an adjustable-gain LNA and an image-reject downconverter with 35dB image suppression. These features yield excellent combined downconverter noise figure (4dB) and high linearity with an input third-order intercept point (IIP3) of up to +2dBm. The transmitter consists of a double-balanced mixer and a power amplifier (PA) predriver that produces up to 0dBm (in some applications serving as the final power stage). It can be used in a variety of configurations, including BPSK modulation, direct VCO modulation, and transmitter upconversion. For devices featuring transmit as well as receive image rejection, refer to the MAX2420/MAX2421/MAX2422/MAX2460/MAX2463 data sheet. The MAX2424/MAX2426 have an on-chip local oscillator (LO), requiring only an external varactor-tuned LC tank for operation. The integrated divide-by-64/65 dual-modulus prescaler can also be set to a direct mode, in which it acts as an LO buffer amplifier. Four separate powerdown inputs can be used for system power management, including a 0.5µA shutdown mode. The MAX2424/MAX2426 come in a 28-pin SSOP package. MAX2424/MAX2426 900MHz Image-Reject Receiver with Transmit Mixer ABSOLUTE MAXIMUM RATINGS VCC to GND ...........................................................-0.3V to +5.5V TXIN, TXIN Differential Voltage ..............................................+2V Voltage on TXOUT......................................-0.3V to (VCC + 1.0V) Voltage on LNAGAIN, TXON, RXON, VCOON, DIV1, MOD, TXIN, TXIN............................-0.3V to (VCC + 0.3V) RXIN Input Power..............................................................10dBm TANK, TANK Input Power ...................................................2dBm Continuous Power Dissipation (TA = +70°C) SSOP (derate 9.50mW/°C above +70°C) ......................762mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +165°C Lead Temperature (soldering, 10sec) .............................+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. DC ELECTRICAL CHARACTERISTICS (VCC = +2.7V to +4.8V, no RF signals applied, LNAGAIN = Unconnected, VTXIN = V TXIN = 2.3V, VVCOON = 2.4V, VRXON = VTXON = VMOD = VDIV1 = 0.45V, PREGND = GND, TA = -40°C to +85°C. Typicals are at TA = +25°C, VCC = 3.3V, unless otherwise noted.) CONDITIONS PARAMETER Supply-Voltage Range Oscillator Supply Current MIN TYP 2.7 PREGND = unconnected Prescaler Supply Current (÷ 64/65 mode) (Note 1) MAX UNITS 4.8 V 9.5 14 mA 4.2 6 mA Prescaler Supply Current (buffer mode) (Note 2) VDIV1 = 2.4V 5.4 8.5 mA Receive Supply Current (Note 3) VRXON = 2.4V, PREGND = unconnected 23 36 mA Transmitter Supply Current (Note 4) VRXON = 0.45V, VTXON = 2.4V, PREGND = unconnected 20 32 mA Shutdown Supply Current VCOON = RXON = TXON TA = +25°C = MOD = DIV1 = GND TA = -40°C to +85°C Digital Input Voltage High RXON, TXON, DIV1, VCOON, MOD Digital Input Voltage Low RXON, TXON, DIV1, VCOON, MOD Digital Input Current Voltage on any one digital input = VCC or GND 0.5 10 2.4 µA V ±1 0.45 V ±10 µA Note 1: Calculated by measuring the combined oscillator and prescaler supply current and subtracting the oscillator supply current. Note 2: Calculated by measuring the combined oscillator and LO buffer supply current and subtracting the oscillator supply current. Note 3: Calculated by measuring the combined receive and oscillator supply current and subtracting the oscillator supply current. With LNAGAIN = GND, the supply current drops by 4.5mA. Note 4: Calculated by measuring the combined transmit and oscillator supply current and subtracting the oscillator supply current. 2 _______________________________________________________________________________________ 900MHz Image-Reject Receiver with Transmit Mixer (MAX2424/MAX2426 EV kit, VCC = +3.3V, fRXIN = 915MHz, PRXIN = -35dBm, VTXIN = V TXIN = 2.3V (DC bias), VTXIN = 250mVp-p, fTXIN = 1MHz, VLNAGAIN = 2V, VVCOON = 2.4V, RXON = TXON = MOD = DIV1 = PREGND = GND, TA = +25°C, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS 1000 MHz RECEIVER (VRXON = 2.4V, fLO = 925.7MHz (MAX2424), fLO = 985MHz (MAX2426)) Input Frequency Range IF Frequency Range (Notes 5, 6) 800 MAX2424 (Notes 5, 6) 8.5 10.7 12.5 MAX2426 (Notes 5, 6) 55 70 85 Image Frequency Rejection Conversion Power Gain Noise Figure Input Third-Order Intercept (IIP3) Input 1dB Compression 26 35 VLNAGAIN = VCC, TA = +25°C (Note 7) MAX2424 20 22 24.5 MAX2426 19 21 23.5 VLNAGAIN = VCC, TA = -40°C to +85°C (Notes 5, 7) MAX2424 19 25 MAX2426 18 24 VLNAGAIN = 1V (Note 7) 12 LNAGAIN = GND (Note 7) -16 LNAGAIN = VCC (Notes 5, 7) 4 VLNAGAIN = 1V (Notes 5, 7) 12 LNAGAIN = VCC (Notes 5, 8) -19 dB 5 -17 VLNAGAIN = 1V (Notes 5, 8) -8 LNAGAIN = VCC -26 VLNAGAIN = 1V -18 MHz dB dB dB dBm LO to RXIN Leakage Receiver on or off -60 dBm Receiver Turn-On Time (Note 9) 500 ns TRANSMITTER (VTXON = 2.4V, fLO = 915MHz) Output Frequency Range (Notes 5, 10) 800 TA = +25°C -9.5 TA = TMIN to TMAX (Note 5) -10 Baseband 3dB Bandwidth Output Power 125 Output 1dB Compression Output Third-Order Intercept (OIP3) 1000 (Note 11) -7 MHz MHz -5 -4.5 dBm -0.5 dBm 3.5 dBm Carrier Suppression 30 dBc Output Noise Density -140 dBm/Hz 220 ns Transmitter Turn-On Time (Note 12) _______________________________________________________________________________________ 3 MAX2424/MAX2426 AC ELECTRICAL CHARACTERISTICS MAX2424/MAX2426 900MHz Image-Reject Receiver with Transmit Mixer AC ELECTRICAL CHARACTERISTICS (continued) (MAX2424/MAX2426 EV kit, VCC = +3.3V, fRXIN = 915MHz, PRXIN = -35dBm, VTXIN = V TXIN = 2.3V (DC bias), VTXIN = 250mVp-p, fTXIN = 1MHz, VLNAGAIN = 2V, VVCOON = 2.4V, RXON = TXON = MOD = DIV1 = PREGND = GND, TA = +25°C, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS 1100 MHz OSCILLATOR AND PRESCALER Oscillator Frequency Range (Note 5) Oscillator Phase Noise 10kHz offset (Note 13) 800 MAX2424 82 MAX2426 72 MAX2424 8 MAX2426 35 RX to TX with PRXIN =-45dBm (RX mode) MAX2424 to PRXIN = 0dBm (TX mode) (Note 14) MAX2426 70 Standby to TX or Standby to RX Oscillator Pulling dBc/Hz kHz 110 Prescaler Output Level ZL = 100kΩ | | 10pF Oscillator Buffer Output Level (Notes 5, 13) VDIV1 = 2.4V, ZL = 50Ω, ZL = 50Ω Required Modulus Setup Time (Notes 5, 15) ÷ 64/65 mode 10 ns Required Modulus Hold Time (Notes 5, 15) ÷ 64/65 mode 0 ns Note 5: Note 6: Note 7: Note 8: Note 9: Note 10: Note 11: Note 12: Note 13: Note 14: Note 15: 4 500 TA = +25°C -11 TA = -40°C to +85°C -12 -8 mVp-p dBm Guaranteed by design and characterization. Image rejection typically falls to 30dBc at the frequency extremes. Refer to the Typical Operating Characteristics for a plot showing Receiver Gain vs. LNAGAIN Voltage, Input IP3 vs. LNAGAIN Voltage, and Noise Figure vs. LNAGAIN Voltage. Two tones at PRXIN = -45dBm each, f1 = 915.0MHz and f2 = 915.2MHz. Time delay from VRXON = 0.45V to VRXON = 2.4V transition to the time the output envelope reaches 90% of its final value. Output power typically falls to -10dBm at the frequency extremes. Two tones at VTXIN = 125mVp-p, f1 = 1.0MHz, and f2 = 1.2MHz. Time delay from VTXON = 0.45V to VTXON = 2.4V transition to the time the output envelope reaches 90% of its final value. Using tank components L3 = 5.0nH (Coilcraft A02T), C2 = C3 = C26 = 3.3pF, R6 = R7 = 10Ω. This approximates a typical application in which TXOUT is followed by an external PA and a T/R switch with finite isolation. Relative to the rising edge of PREOUT. _______________________________________________________________________________________ 900MHz Image-Reject Receiver with Transmit Mixer 37 31 3.0 ICC (µA) ICC (mA) 32 VCC = 3.3V 29 VCC = 2.7V RXON = VCC PREGND = UNCONNECTED INCLUDES OSCILLATOR CURRENT 26 TXON = VCC PREGND = UNCONNECTED INCLUDES OSCILLATOR CURRENT 25 23 21 24 -20 20 40 60 80 VCC = 4.8V -40 -20 0 20 40 60 VCC = 3.3V 1.0 0.5 VCC = 2.7V 0 -40 80 -20 0 20 40 60 TEMPERATURE (°C) TEMPERATURE (°C) RECEIVER GAIN vs. LNAGAIN RECEIVER INPUT IP3 vs. LNAGAIN RECEIVER NOISE FIGURE vs. LNAGAIN 5 LNA OFF 0 15 LNA ADJUSTABLE MAX PARTIALLY GAIN GAIN BIASED 5 ADJUSTABLE GAIN 0 IIP3 (dBm) 10 MAX GAIN -10 -5 AVOID THIS REGION -10 -15 25 20 15 10 0 -20 1.0 1.5 2.0 0 0.5 1.0 RXON = VCC DIV1 = VCC AVOID THIS REGION 5 RXON = VCC -20 0.5 LNA ADJUSTABLE MAX PARTIALLY GAIN GAIN BIASED -15 RXON = VCC 0 LNA OFF 30 AVOID THIS REGION -5 1.5 0 2.0 0.5 1.0 1.5 LNAGAIN VOLTAGE (V) LNAGAIN VOLTAGE (V) LNAGAIN VOLTAGE (V) MAX2424 RECEIVER GAIN vs. TEMPERATURE RECEIVER NOISE FIGURE vs. TEMPERATURE AND SUPPLY VOLTAGE RECEIVER INPUT IP3 vs. TEMPERATURE 22 VCC = 3.3V 20 VCC = 2.7V MAX2424/6-09 MAX2424/6-08 VCC = 4.8V 2.0 -6 VLNAGAIN = 1V -8 -10 4.5 VCC = 3.3V 4.0 VCC = 2.7V IIP3 (dBm) VCC = 4.8V LNAGAIN = VCC RXON = VCC DIV1 = VCC 5.0 NOISE FIGURE (dB) 24 5.5 MAX2424/6-07 LNAGAIN = VCC RXON = VCC 80 40 35 NOISE FIGURE (dB) LNA PARTIALLY BIASED MAX2424/6-05 LNA OFF 26 2.0 TEMPERATURE (°C) 25 20 0 MAX2424/6-04 -40 2.5 1.5 27 28 RECEIVER GAIN (dB) VCC = 4.8V 33 34 30 RECEIVER GAIN (dB) 3.5 35 VCC = 2.7V 36 VCOON = GND 4.0 MAX2424/6-06 VCC = 3.3V 4.5 MAX2424/6-02 VCC = 4.8V 38 ICC (mA) 39 MAX2424/6-01 42 40 SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE TRANSMITTER SUPPLY CURRENT vs. TEMPERATURE MAX2424/6-03 RECEIVER SUPPLY CURRENT vs. TEMPERATURE -12 -14 -16 VLNAGAIN = 2V 3.5 -18 18 RXON = VCC 3.0 -40 -20 0 20 40 TEMPERATURE (°C) 60 80 -20 -40 -20 0 20 40 TEMPERATURE (°C) 60 80 -40 -20 0 20 40 60 80 TEMPERATURE (°C) _______________________________________________________________________________________ 5 MAX2424/MAX2426 __________________________________________Typical Operating Characteristics (MAX2424/MAX2426 EV kit, VCC = +3.3V; fLO(RX) = 925.7MHz (MAX2424), 985MHz (MAX2426); fRXIN = 915MHz, PRXIN = -35dBm, fLO(TX) = 915MHz, VTXIN = V TXIN = 2.3V (DC bias), VTXIN = 250mVp-p, fTXIN = 1MHz, VLNAGAIN = 2V, VVCOON = 2.4V, RXON = TXON = MOD = DIV1 = PREGND = GND, TA = +25°C, unless otherwise noted.) ______________________________Typical Operating Characteristics (continued) (MAX2424/MAX2426 EV kit, VCC = +3.3V; fLO(RX) = 925.7MHz (MAX2424), 985MHz (MAX2426); fRXIN = 915MHz, PRXIN = -35dBm, fLO(TX) = 915MHz, VTXIN = V TXIN = 2.3V (DC bias), VTXIN = 250mVp-p, fTXIN = 1MHz, VLNAGAIN = 2V, VVCOON = 2.4V, RXON = TXON = MOD = DIV1 = PREGND = GND, TA = +25°C, unless otherwise noted.) 50 VCC = 2.7V -6 VCC = 3.3V -7 -8 40 30 20 10 MAX2424 35 IMAGE REJECTION (dB) -5 40 MAX2424/6-11 1dB COMPRESSION POINT (dBm) RXON = VCC IMAGE REJECTION (dB) VCC = 4.8V -4 RECEIVER IMAGE REJECTION vs. IF FREQUENCY 60 MAX2424/6-10 -3 RECEIVER IMAGE REJECTION vs. RF FREQUENCY MAX2426 30 25 20 15 0 10 -10 5 -20 0 RXON = VCC 20 40 60 0 80 400 800 TEMPERATURE (°C) RXIN INPUT IMPEDANCE vs. FREQUENCY 45 40 -80 35 IMAGINARY 30 25 -60 REAL 20 -40 15 10 5 -100 1600 2000 TXON = VCC VCC = 4.8V VCC = 3.3V -10 -15 0 -25 5 800 1000 1200 1400 FREQUENCY (MHz) TXOUT OUTPUT IMPEDANCE vs. FREQUENCY 100 REAL IMAGINARY -100 -150 -200 TXON = VCC 600 800 1000 1200 1400 1600 1800 2000 FREQUENCY (MHz) VCC = 2.7V VCC = 3.3V TXON = VCC -40 -20 0 20 40 60 80 TRANSMITTER 1dB COMPRESSION POINT vs. TEMPERATURE LO -40 -50 -60 -80 -250 VCC = 4.8V TEMPERATURE (°C) -70 -300 6 1000 DOUBLE-SIDE BAND FUNDAMENTAL TXON = VCC -20 -30 0 -50 100 INPUT VOLTAGE (mVp-p) 0 -10 POWER (dBm) 50 -2 -3 -4 -5 -6 -7 -8 -9 -10 -11 -12 -13 TRANSMITTER OUTPUT SPECTRUM MAX2424/6-16 REAL OR IMAGINARY IMPEDANCE (Ω) 150 1000 -14 10 1 OUTPUT 1dB COMPRESSION (dBm) 600 MAX2424/6-17 0 100 TRANSMITTER OUTPUT POWER vs. TEMPERATURE VCC = 2.7V -20 10 TRANSMITTER OUTPUT POWER vs. INPUT VOLTAGE -5 -20 1 IF FREQUENCY (MHz) 0 OUTPUT POWER (dBm) RXON = VCC IMAGINARY IMPEDANCE (Ω) MAX2424/6-13 50 1200 RF FREQUENCY (MHz) MAX2424/6-15 0 RXON = VCC MAX2424/6-18 -20 OUTPUT POWER (dBm) -40 MAX2424/6-14 -9 MAX2424/6-12 MAX2424 RECEIVER OUTPUT 1dB COMPRESSION POINT vs. TEMPERATURE REAL IMPEDANCE (Ω) MAX2424/MAX2426 900MHz Image-Reject Receiver with Transmit Mixer VCC = 4.8V 0 -1 -2 VCC = 3.3V -3 -4 VCC = 2.7V -5 -6 -90 -100 -7 910 911 912 913 914 915 916 917 918 919 920 FREQUENCY (MHz) TXON = VCC -40 -20 0 20 40 TEMPERATURE (°C) _______________________________________________________________________________________ 60 80 900MHz Image-Reject Receiver with Transmit Mixer TRANSMITTER BASEBAND FREQUENCY RESPONSE TXON = VCC NOTE: TXIN IS TOTAL VOLTAGE FOR TWO TONES (PEAK-TO-PEAK) 0 -10 -30 -40 TXOUT (dBc) POWER (dBm) -20 FUNDAMENTAL -50 -60 IM3 LEVEL -70 -80 -90 -100 10 100 1000 3 0 -3 -6 -9 -12 -15 -18 -21 -24 -27 -30 -33 -36 MAX2424/6-20 10 MAX2424/6-19 POWER vs. TXIN VOLTAGE TXON = VCC 1 10 100 1000 FREQUENCY (MHz) TXIN VOLTAGE (mVp-p) ______________________________________________________________Pin Description PIN NAME FUNCTION 1 VCC 2 CAP1 3 RXOUT 4 GND Ground Connection 5 RXIN Receiver RF Input, single ended. The input match shown in Figure 1 maintains an input VSWR of better than 2:1 from 902MHz to 928MHz. 6 VCC Supply Voltage Input for the Receive Low-Noise Amplifier. Bypass with a 47pF low-inductance capacitor to GND (pin 7 recommended). 7 GND Ground Connection for Receive Low-Noise Amplifier. Connect directly to ground plane using multiple vias. 8 GND Ground Connection for Signal-Path Blocks, except LNA 9 TXOUT Supply-Voltage Input for Master Bias Cell. Bypass with a 47pF low-inductance capacitor and 0.1µF to GND (pin 28 recommended). Receive Bias Compensation Pin. Bypass with a 47pF low-inductance capacitor and 0.01µF to GND. Do not make any other connections to this pin. Single-ended, 330Ω IF Output. AC couple to this pin. PA Predriver Output. See Figure 1 for an example matching network, which provides better than 2:1 VSWR from 902MHz to 928MHz. 10 LNAGAIN Low-Noise Amplifier Gain-Control Input. Drive this pin high for maximum gain. When LNAGAIN is pulled low, the LNA is capacitively bypassed and the supply current is reduced by 4.5mA. This pin can also be driven with an analog voltage to adjust the LNA gain in intermediate states. Refer to the Receiver Gain vs. LNAGAIN Voltage graph in the Typical Operating Characteristics, as well as Table 1. 11 VCC Supply Voltage Input for the Signal-Path Blocks, except LNA. Bypass with a 47pF low-inductance capacitor and 0.01µF to GND (pin 8 recommended). _______________________________________________________________________________________ 7 MAX2424/MAX2426 ______________________________Typical Operating Characteristics (continued) (MAX2424/MAX2426 EV kit, VCC = +3.3V; fLO(RX) = 925.7MHz (MAX2424), 985MHz (MAX2426); fRXIN = 915MHz, PRXIN = -35dBm, fLO(TX) = 915MHz, VTXIN = V TXIN = 2.3V (DC bias), VTXIN = 250mVp-p, fTXIN = 1MHz, VLNAGAIN = 2V, VVCOON = 2.4V, RXON = TXON = MOD = DIV1 = PREGND = GND, TA = +25°C, unless otherwise noted.) MAX2424/MAX2426 900MHz Image-Reject Receiver with Transmit Mixer _________________________________________________Pin Description (continued) 8 PIN NAME FUNCTION 12 TXIN Transmit Mixer’s Noninverting Baseband/IF Input. TXIN, TXIN form a high-impedance, differential input port. See Figure 1. 13 TXIN Transmit Mixer’s Inverting Baseband/IF Input. TXIN, TXIN form a high-impedance, differential input port. See Figure 1. 14 CAP2 Transmit Bias Compensation Input. Bypass with a 47pF low-inductance capacitor and 0.01µF to GND. Do not make any other connections to this pin. 15 TXON Drive TXON and VCOON with a logic high to enable the transmit IF variable-gain amplifier, upconverter mixer, and PA predriver. See Power Management section. 16 RXON Drive RXON and VCOON with a logic high to enable the LNA, receive mixer, and IF output buffer. See Power Management section. 17 VCOON Drive VCOON with a logic high to turn on the VCO, phase shifters, VCO buffers, and prescaler. To disable the prescaler, leave the PREGND pin unconnected. 18 DIV1 Drive DIV1 with a logic high to disable the divide-by-64/65 prescaler and connect the PREOUT pin directly to an oscillator buffer amplifier, which outputs -8dBm into a 50Ω load. Drive DIV1 low for divideby-64/65 operation. Drive this pin low when in shutdown to minimize shutdown current. 19 MOD Modulus Control for the Divide-by-64/65 Prescaler. Drive MOD high for divide-by-64 mode. Drive MOD low for divide-by-65 mode. 20 PREGND Ground connection for the Prescaler. Connect PREGND to ground for normal operation. Leave unconnected to disable the prescaler and the output buffer. Connect MOD and DIV1 to ground and leave PREOUT unconnected when disabling the prescaler. 21 PREOUT Prescaler/Oscillator Buffer Output. In divide-by-64/65 mode (DIV1 = low), the output level is 500mVp-p into a high-impedance load. In divide-by-1 mode (DIV1 = high), this output delivers -8dBm into a 50Ω load. AC couple to this pin. 22 VCC Supply-Voltage Input for Prescaler. Bypass with a 47pF low-inductance capacitor and 0.01µF to GND (pin 20 recommended). 23 VCC Supply-Voltage Input for VCO and Phase Shifters. Bypass with a 47pF low-inductance capacitor to GND (pin 26 recommended). 24 TANK Differential Oscillator Tank Port. See Applications Information for information on tank circuits or on using an external oscillator. 25 TANK Differential Oscillator Tank Port. See Applications Information for information on tank circuits or on using an external oscillator. 26 GND Ground Connection for VCO and Phase Shifters 27 GND Ground (substrate) 28 GND Ground Connection for Master Bias Cell _______________________________________________________________________________________ 900MHz Image-Reject Receiver with Transmit Mixer VCC 1 0.1µF VCC VCC 22 47pF 47pF 28 GND PREGND 0.01µF 20 VCO TANK COMPONENTS FOR 915MHz RF FREQUENCY VCC 2 0.1µF CAP1 VCC 23 DEVICE L3 (nH) C2, C3 (pF) C26 (pF) R6, R7 (Ω) 26 MAX2424 6.8 3.3 2.0 10 27 MAX2426 3.3 8.0 4.0 20 47pF 47pF GND RECEIVE RF INPUT MAX2424/MAX2426 VCC 8.2nH 5 RXIN 47pF MAX2424 MAX2426 GND 0.01µF RXOUT 3 RECEIVE IF OUTPUT (330Ω) VCC 12nH 0.01µF* 47pF MODULATOR INPUT 22nH TXIN 47pF 9 18nH TRANSMIT RF OUTPUT 12 10k TXOUT RA TXIN RB VCC 10k 13 MODULATOR INPUT 0.01µF* VCC 6 47pF 7 100nH GND VCC 11 0.01µF VARACTORS: ALPHA SMV1299-004 OR EQUIVALENT 1k VCC VCC TANK 25 R7 C2 47k 47pF C26 L3 8 GND TANK 24 R6 1000pF 14 0.01µF CAP2 PREOUT 47pF MOD DIV1 VCOON 10 LNAGAIN LNAGAIN RXON GND TXON 21 19 18 17 16 C3 15 1k TO PLL MOD DIV1 VCOON RXON 47pF 4 VCO ADJUST 47pF TXON * WHEN USING DIFFERENTIAL SOURCE, REMOVE RESISTORS AND REPLACE CAPACITORS WITH SHORTS. FOR SINGLE-ENDED SOURCE, DRIVE ONLY MODULATOR INPUT. CHOOSE RA AND RB VALUES AS SHOWN IN TRANSMITTER SECTION. Figure 1. Typical Operating Circuit _______________________________________________________________________________________ 9 MAX2424/MAX2426 900MHz Image-Reject Receiver with Transmit Mixer _______________Detailed Description The following sections describe each of the functional blocks shown in the Functional Diagram. MAX2424 MAX2426 Receiver The MAX2424/MAX2426’s receive path consists of a 900MHz low-noise amplifier, an image-reject mixer, and an IF buffer amplifier. The LNA’s gain and biasing are adjustable via the LNAGAIN pin. Proper operation of this pin provides optimum performance over a wide range of signal levels. The LNA has four modes determined by the DC voltage applied on the LNAGAIN pin. See Table 1, as well as the relevant Typical Operating Characteristics plots. At low LNAGAIN voltages, the LNA is shut off and the input signal capacitively couples directly into mixer to provide maximum linearity for large-signal operation (receiver close to transmitter). As the LNAGAIN voltage increases, the LNA turns on. Between 0.5V and 1V at LNAGAIN, the LNA is partially biased and behaves like a Class C amplifier. Avoid this operating mode for applications where linearity is a concern. As the LNAGAIN voltage reaches 1V, the LNA is fully biased into Class A mode, and the gain is monotonically adjustable for LNAGAIN voltages above 1V. See the receiver gain, IP3, and Noise Figure vs. LNAGAIN plots in the Typical Operating Characteristics for more information. The downconverter is implemented using an imagereject mixer consisting of an input buffer with two outputs, each of which is fed to a double-balanced mixer. A quadrature LO drives the local-oscillator (LO) port of Table 1. LNA Modes LNAGAIN VOLTAGE (V) 0 < VLNAGAIN ≤ 0.5 MODE LNA capacitively bypassed, minimum gain, maximum IP3 0.5 < VLNAGAIN < 1.0 LNA partially biased. Avoid this mode— the LNA operates in a Class C manner 1.0 < VLNAGAIN ≤ 1.5 LNA gain is monotonically adjustable 1.5 < VLNAGAIN ≤ VCC LNA at maximum gain (remains monotonic) 10 TXIN 1.5µA 2M VMIXER INPUT TXIN 1.5µA Figure 2. TXIN, TXIN Equivalent Circuit each mixer. An on-chip oscillator and an external tank circuit generates the LO. Its signal is buffered and split into two phase shifters, which provide 90° of phase shift across their outputs. This pair of LO signals is fed to the mixers. The mixers’ outputs then pass through a second pair of phase shifters, which provide a 90° phase shift across their outputs. The resulting mixer outputs are then summed together. The final phase relationship is such that the desired signal is reinforced and the image signal is canceled. The downconverter mixer output appears on the RXOUT pin, a single-ended 330Ω output. Transmitter The MAX2424/MAX2426 transmitter consists of a balanced mixer and a PA driver amplifier. The mixer inputs are accessible via the TXIN and TXIN pins. An equivalent circuit for the TXIN and TXIN pins is shown in Figure 2. Because TXIN and TXIN are linearly coupled to the mixer stage, they can accept spectrally shaped input signals. Typically, the mixer can be used to multiply the LO with a baseband signal, generating BPSK or ASK modulation. Transmit upconversion can also be implemented by applying a modulated IF signal to these inputs. For applications requiring image rejection on the transmitter, refer to the MAX2420/MAX2421/ MAX2422/MAX2460/MAX2463 data sheet. Set the common-mode voltage at TXIN, TXIN to 2.3V by selecting appropriate values for RA and RB (Figure 1). The total series impedance of RA and RB should be approximately 100kΩ. Frequency modulation (FM) is realized by modulating the VCO tuning voltage. Apply the appropriate differential and common-mode voltages to TXIN and TXIN to control transmitter output power (Figure 3). ______________________________________________________________________________________ 900MHz Image-Reject Receiver with Transmit Mixer R1 The MAX2424/MAX2426 uses passive networks to provide quadrature phase shifting for the receive IF and LO signals. Because these networks are frequency selective, both the RF and IF frequency operating ranges are limited. Image rejection degrades as the IF and RF moves away from the designed optimum frequencies. The MAX2424/MAX2426’s phase shifters are arranged such that the LO frequency is higher than the RF carrier frequency (high-side injection). MAX2424 MAX2426 i 1.5µA TXIN 2M R2 TXIN Local Oscillator (LO) 1.5µA R3 The on-chip LO is formed by an emitter-coupled differential pair. An external LC resonant tank sets the oscillation frequency. A varactor diode is typically used to create a voltage-controlled oscillator (VCO). See the Applications Information section for an example VCO tank circuit. RT = R1 + R2 + R3 VDIFF = VTXIN - V TXIN Figure 3. Biasing TXIN and TXIN for FM For example, if VCC = 3.3V and POUT = -8dBm, choose RT = 100kΩ for sufficient current through the divider, so that bias currents for TXIN and TXIN have little effect over temperature. Set VTXIN = 2.3V to satisfy commonmode voltage range requirements at VCC = 3.3V. Use the Transmit Output Power vs. Input Voltage graph in the Typical Operating Characteristics to determine the input voltage (in mVp-p) required to produce the desired output. Divide this value by 2√2 and use it for VDIFF. A -8dBm transmitter output requires 250mVp-p / 2√2 = 88.4mV. VTXIN = 2.3V + 0.0884V = 2.3884V RT = R1 + R2 + R3 Solve for resistors R1, R2, and R3 with the following equations: R3 = V TXIN x RT ( VCC R2 = VTXIN – V TXIN ) x VR T CC R1 = RT – R2 – R3 Since the transmit and receive sections typically require different LO frequencies, it is not recommended to have both transmit and receive active at the same time. The LO may be overdriven in applications where an external signal is available. The external LO signal should be about 0dBm from 50Ω, and should be AC coupled into either the TANK or TANK pin. Both TANK and TANK require pull-up resistors to V CC. See the Applications Information section for details. The local oscillator resists pulling caused by changes in load impedance that occur as the part is switched from standby mode, with just the oscillator running to either transmit or receive mode. The amount of LO pulling is affected if a signal is present at the RXIN port in transmit mode. The most common cause of pulling is imperfect isolation in an external transmit/ receive (T/R) switch. The AC Electrical Characteristics table contains specifications for this case as well. Prescaler The on-chip prescaler operates in two different modes: as a dual-modulus divide-by-64/65, or as an oscillator buffer amplifier. The DIV1 pin controls this function. When DIV1 is low, the prescaler is in dual-modulus divide-by-64/65 mode; when it is high, the prescaler is disabled and the oscillator buffer amplifier is enabled. The buffer typically outputs -8dBm into a 50Ω load. To minimize shutdown supply current, pull the DIV1 pin low when in shutdown mode. In divide-by-64/65 drive mode, the division ratio is controlled by the MOD pin. Drive MOD high to operate the prescaler in divide-by-64 mode. Drive MOD and DIV1 low to operate the prescaler in divide-by-65 mode. ______________________________________________________________________________________ 11 MAX2424/MAX2426 Phase Shifter VCC MAX2424/MAX2426 900MHz Image-Reject Receiver with Transmit Mixer To disable the prescaler entirely, leave PREGND and PREOUT unconnected. Also connect the MOD and DIV1 pins to GND. Disabling the prescaler does not affect operation of the VCO stage. Power Management The MAX2424/MAX2426 supports four different powermanagement features to conserve battery life. The VCO section has its own control pin (VCOON), which also serves as a master bias pin. When VCOON is high, the LO, quadrature LO phase shifters, and prescaler or LO buffer are all enabled. Stabilize VCO by powering it up prior to transmitting or receiving. For transmit-to-receive switching, the receiver and transmitter sections have their own enable control inputs, RXON and TXON. With VCOON high, bringing RXON high enables the receive path, which consists of the LNA, image-reject mixers, and IF output buffer. When this pin is low, the receive path is inactive. The TXON input enables the upconverter mixer and PA predriver. VCOON must be high for the transmitter to operate. When TXON is low, the transmitter is off. To disable all chip functions and reduce the supply current to typically 0.5µA, pull VCOON, DIV1, MOD, RXON, and TXON low. Choose tank components according to your application needs, such as phase-noise requirements, tuning range, and VCO gain. High Q inductors such as aircore micro springs yield low phase noise. Use a lowtolerance inductor (L3) for predictable oscillation frequency. Resistors R6 and R7 can be chosen from 0 to 20Ω to reduce the Q of parasitic resonance due to series package inductance LT. Keep R6 and R7 as small as possible to minimize phase noise, yet large enough to ensure oscillator start-up in fundamental mode. Oscillator start-up with be most critical with high tuning bandwidth (low tank Q) and high temperature. Capacitors C2 and C3 couple in the varactor. Light coupling of the varactor is a way to reduce the effects of high varactor tolerance and increase loaded Q. For a wider tuning range, use larger values for C2 and C3 or a varactor with a large capacitance ratio. Capacitor C26 is used to trim the tank oscillator frequency. Larger values for C26 will help negate the effect of stray PCB capacitance and parasitic inductor capacitance (L3). Choose a low-tolerance capacitor for C26. VCC ___________Applications Information Oscillator Tank The on-chip oscillator requires a parallel-resonant tank circuit connected across TANK and TANK. Figure 4 shows an example of an oscillator tank circuit. Inductor L4 provides DC bias to the tank ports. Inductor L3, capacitor C26, and the series combination of capacitors C2, C3, and both halves of the varactor diode capacitance set the resonant frequency as follows: fr = CEFF = 1 ( )( MAX2424 MAX2426 TANK ) 1 + C26 1 1 2 C2 + C3 + C D1 R7 C2 R5 1k 1/2 D1 L3 6.8nH R6 TANK 2π L3 CEFF L4 100nH VCO_CTRL C26 C3 1/2 D1 C1 47pF R4 1k D1 = ALPHA SMV1299-004 SEE FIGURE 1 FOR R6, R7, C2, C3, C26, AND L3 COMPONENT VALUES. Figure 4. Oscillator Tank Schematic Using the On-Chip VCO where CD1 is the capacitance of one varactor diode. 12 R8 47k ______________________________________________________________________________________ 900MHz Image-Reject Receiver with Transmit Mixer TANK L3 L1 MAX2424/MAX2426 LT MAX2424 MAX2426 R1 1/2 D1 L4 R2 VTUNE Ci C2 VCC C1 1/2 D1 L2 LT R3 L5 TANK Figure 5. Series-Coupled Resonant Tank for Wide Tuning Range and Low Phase Noise For applications that require a wide tuning range and low phase noise, a series-coupled resonant tank may be required as shown in Figure 5. This tank will use the package inductance in series with inductors L1, L2, and capacitance of varactor D1 to set the net equivalent inductance which resonates in parallel with the internal oscillator capacitance. Inductors L1 and L2 may be implemented as microstrip inductors, saving component cost. Bias is provided to the tank port through chokes L3 and L5. R1 and R3 should be chosen large enough to de-Q the parasitic resonance due to L3 and L5 but small enough to minimize the voltage drop across them due to bias current. Values for R1 and R3 should be kept between 0 and 50Ω. Proper high frequency bypassing (C1) should be used for the bias voltage to eliminate power supply noise from entering the tank. Oscillator Tank PC Board Layout The parasitic PC board capacitance, as well as PCB trace inductance and package inductance, affect oscillation frequency, so be careful in laying out the PC board for the oscillator tank. Keep the tank layout as symmetrical, tightly packed, and close to the device as possible to minimize LO feedthrough. When using a PC board with a ground plane, a cut-out in the ground plane (and any other planes) below the oscillator tank reduces parasitic capacitance. VCC MAX2424 50Ω 47pF TANK VCC 50Ω 50Ω EXT LO TANK 50Ω EXTERNAL LO LEVEL IS 0dBm FROM A 50Ω SOURCE. 47pF Figure 6. Using an External Local Oscillator Using an External Oscillator If an external 50Ω LO signal source is available, it can be used as an input to the TANK or TANK pin in place of the on-chip oscillator (Figure 6). The oscillator signal is AC coupled into the TANK pin and should have a level of about 0dBm from a 50Ω source. For proper biasing of the oscillator input stage, pull up the TANK and TANK pins to the VCC supply via 50Ω resistors. If a differential LO source such as the MAX2620 is available, AC-couple the inverting output into TANK. ______________________________________________________________________________________ 13 _________________________________________________________Functional Diagram LNAGAIN 90° Σ RXIN RXOUT 0° DIV1 MOD CAP1 RXON TXON CAP2 0° 90° ÷ 1/64/65 BIAS PREOUT PREGND TANK PHASE SHIFTER TANK VCOON 0° TXOUT MAX2424 MAX2426 TXIN TXIN ________________________________________________________Package Information SSOP.EPS MAX2424/MAX2426 900MHz Image-Reject Receiver with Transmit Mixer 14 ______________________________________________________________________________________