19-3272; Rev 3; 12/10 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver The MAX1471 low-power, CMOS, superheterodyne, RF dual-channel receiver is designed to receive both amplitude-shift-keyed (ASK) and frequency-shift-keyed (FSK) data without reconfiguring the device or introducing any time delay normally associated with changing modulation schemes. The MAX1471 requires few external components to realize a complete wireless RF digital data receiver for the 300MHz to 450MHz ISM bands. The MAX1471 includes all the active components required in a superheterodyne receiver including: a lownoise amplifier (LNA), an image-reject (IR) mixer, a fully integrated phase-locked loop (PLL), local oscillator (LO), 10.7MHz IF limiting amplifier with received-signalstrength indicator (RSSI), low-noise FM demodulator, and a 3V voltage regulator. Differential peak-detecting data demodulators are included for both the FSK and ASK analog baseband data recovery. The MAX1471 includes a discontinuous receive (DRX) mode for lowpower operation, which is configured through a serial interface bus. Features o ASK and FSK Demodulated Data on Separate Outputs o Specified over Automotive -40°C to +125°C Temperature Range o Low Operating Supply Voltage Down to 2.4V o On-Chip 3V Regulator for 5V Operation o Low Operating Supply Current 7mA Continuous Receive Mode 1.1µA Deep-Sleep Mode o Discontinuous Receive (DRX) Low-Power Management o Fast-On Startup Feature < 250µs o Integrated PLL, VCO, and Loop Filter o 45dB Integrated Image Rejection o RF Input Sensitivity* ASK: -114dBm FSK: -108dBm The MAX1471 is available in a 32-pin thin QFN package and is specified over the automotive -40°C to +125°C temperature range. o Selectable IF BW with External Filter o Programmable Through Serial User Interface o RSSI Output and High Dynamic Range with AGC Applications *0.2% BER, 4kbps, Manchester-encoded data, 280kHz IF BW Automotive Remote Keyless Entry (RKE) Pin Configuration SCLK DIO CS FDATA + Wireless Keys HVIN Wireless Sensors ADATA TOP VIEW PDMINA Garage Door Openers PDMAXA Tire Pressure Monitoring Systems 32 31 30 29 28 27 26 25 Security Systems DSA- 1 24 DVDD Medical Systems DSA+ 2 23 DGND Home Automation OPA+ 3 22 DFF DFA 4 21 OPF+ XTAL2 5 20 DSF+ XTAL1 6 19 DSF- AVDD 7 18 PDMAXF LNAIN 8 17 PDMINF 10 11 12 13 14 15 16 IFIN- 9 IFIN+ 32 Thin QFN-EP** AGND -40°C to +125°C +Denotes a lead(Pb)-free/RoHS-compliant package. /V denotes an automotive qualified part. **EP = Exposed pad. MIXIN- MAX1471ATJ/V+ PIN-PACKAGE MIXOUT TEMP RANGE MIXIN+ PART LNAOUT Ordering Information MAX1471 LNASRC Local Telemetry Systems THIN QFN ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX1471 General Description MAX1471 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver ABSOLUTE MAXIMUM RATINGS High-Voltage Supply, HVIN to DGND ......................-0.3V, +6.0V Low-Voltage Supply, AVDD and DVDD to AGND ....-0.3V, +4.0V SCLK, DIO, CS, ADATA, FDATA ...................................(DGND - 0.3V) to (HVIN + 0.3V) All Other Pins............................(AGND - 0.3V) to (AVDD + 0.3V) Continuous Power Dissipation (TA = +70°C) 32-Pin Thin QFN (derate 21.3mW/°C above +70°C) ...1702mW Operating Temperature Range .........................-40°C to +125°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) ................................ +300°C Soldering Temperature (reflow) ...................................... +260°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 (Typical Application Circuit, VAVDD = VDVDD = VHVIN = +2.4V to +3.6V, fRF = 300MHz to 450MHz, TA = -40°C to +125°C, unless otherwise noted. Typical values are at VAVDD = VDVDD = VHVIN = +3.0V, fRF = 434 MHz, TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS GENERAL CHARACTERISTICS Supply Voltage (5V) HVIN AVDD and DVDD unconnected from HVIN, but connected together 4.5 5.0 5.5 V Supply Voltage (3V) VDD HVIN, AVDD, and DVDD connected to power supply 2.4 3.0 3.6 V Operating 7.0 8.4 mA Polling duty cycle: 10% duty cycle 705 855 DRX mode OFF current 5.0 14.2 Deep-sleep current 1.1 7.1 TA < +85°C Supply Current IDD TA < +105°C (Note 2) TA < +125°C (Note 2) Startup Time tON Operating 8.5 Polling duty cycle: 10% duty cycle 865 DRX mode OFF current 15.5 Deep-sleep current 13.4 Operating 8.6 Polling duty cycle: 10% duty cycle 900 DRX mode OFF current 44.1 Deep-sleep current 36.4 Time for final signal detection, does not include baseband filter settling (Note 2) 200 250 µA mA µA mA µA µs DIGITAL OUTPUTS (DIO, ADATA, FDATA) Output High Voltage VOH ISOURCE = 250µA (Note 2) Output Low Voltage VOL ISINK = 250µA (Note 2) VHVIN 0.15 V 0.15 V DIGITAL INPUTS (CS, DIO, SCLK) Input High Threshold VIH 0.9 x VHVIN Input Low Threshold VIL . 2 _______________________________________________________________________________________ V 0.1 x VHVIN V 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver (Typical Application Circuit, VAVDD = VDVDD = VHVIN = +2.4V to +3.6V, fRF = 300MHz to 450MHz, TA = -40°C to +125°C, unless otherwise noted. Typical values are at VAVDD = VDVDD = VHVIN = +3.0V, fRF = 434 MHz, TA = +25°C, unless otherwise noted.) (Note 1) MAX UNITS Input-High Leakage Current PARAMETER IIH (Note 2) -20 µA Input-Low Leakage Current IIL (Note 2) 20 µA CIN (Note 2) 2.0 pF Input Capacitance SYMBOL CONDITIONS MIN TYP VOLTAGE REGULATOR Output Voltage VREG VHVIN = 5.0V, ILOAD = 7.0mA 3.0 V AC ELECTRICAL CHARACTERISTICS (Typical Application Circuit, VAVDD = VDVDD = VHVIN = +2.4V to +3.6V, fRF = 300MHz to 450MHz, TA = -40°C to +125°C, unless otherwise noted. Typical values are at VAVDD = VDVDD = VHVIN = +3.0V, fRF = 434 MHz, TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS GENERAL CHARACTERISTICS Receiver Sensitivity RFIN Maximum Receiver Input Power Level 0.2% BER, 4kbps Manchester Code, 280kHz IF BW, 50Ω ASK -114 FSK -108 dBm RFMAX Receiver Input Frequency Range fRF Receiver Image Rejection IR 0 300 (Note 3) dBm 450 45 MHz dB LNA/MIXER (Note 4) LNA Input Impedance ZIN_LNA Normalized to 50Ω fRF = 315MHz 1 - j4.7 fRF = 434MHz 1 - j3.4 Voltage Conversion Gain (HighGain Mode) 47.5 dB Input-Referred 3rd-Order Intercept Point (High-Gain Mode) -38 dBm Voltage Conversion Gain (LowGain Mode) 12.2 dB Input-Referred 3rd-Order Intercept Point (Low-Gain Mode) -5 dBm LO Signal Feedthrough to Antenna -90 dBm ZOUT_MIX 330 Ω ZIN_IF 330 Ω fIF 10.7 MHz 10 MHz 2.2 mV/kHz Mixer Output Impedance IF Input Impedance Operating Frequency 3dB Bandwidth FM DEMODULATOR Demodulator Gain GFM _______________________________________________________________________________________ 3 MAX1471 DC ELECTRICAL CHARACTERISTICS (continued) MAX1471 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver AC ELECTRICAL CHARACTERISTICS (continued) (Typical Application Circuit, VAVDD = VDVDD = VHVIN = +2.4V to +3.6V, fRF = 300MHz to 450MHz, TA = -40°C to +125°C, unless otherwise noted. Typical values are at VAVDD = VDVDD = VHVIN = +3.0V, fRF = 434 MHz, TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS ANALOG BASEBAND Maximum Data Filter Bandwidth BWDF 50 kHz Maximum Data Slicer Bandwidth BWDS 100 kHz Maximum Peak Detector Bandwidth BWPD 50 kHz Maximum Data Rate Manchester coded 33 Nonreturn to zero (NRZ) 66 kbps CRYSTAL OSCILLATOR Crystal Frequency fXTAL 9.04 13.728 MHz Frequency Pulling by VDD 3 ppm/V Crystal Load Capacitance 3 pF DIGITAL INTERFACE TIMING (see Figure 8) Minimum SCLK Setup to Falling Edge of CS tSC 30 ns Minimum CS Falling Edge to SCLK Rising-Edge Setup Time tCSS 30 ns Minimum CS Idle Time tCSI 125 ns Minimum CS Period tCS 2.125 µs Maximum SCLK Falling Edge to Data Valid Delay tDO 80 ns Minimum Data Valid to SCLK Rising-Edge Setup Time tDS 30 ns Minimum Data Valid to SCLK Rising-Edge Hold Time tDH 30 ns Minimum SCLK High Pulse Width tCH 100 ns Minimum SCLK Low Pulse Width tCL 100 ns Minimum CS Rising Edge to SCLK Rising-Edge Hold Time tCSH 30 ns Maximum CS Falling Edge to Output Enable Time tDV 25 ns Maximum CS Rising Edge to Output Disable Time tTR 25 ns Note 1: Note 2: Note 3: Note 4: 4 Production tested at TA = +85°C. Guaranteed by design and characterization over entire temperature range. Guaranteed by design and characterization. Not production tested. The oscillator register (0x3) is set to the nearest integer result of fXTAL / 100kHz (see the Oscillator Frequency Register section). Input impedance is measured at the LNAIN pin. Note that the impedance at 315MHz includes the 15nH inductive degeneration from the LNA source to ground. The impedance at 434MHz includes a 10nH inductive degeneration connected from the LNA source to ground. The equivalent input circuit is 50Ω in series with 2.2pF. The voltage conversion gain is measured with the LNA input matching inductor, the degeneration inductor, and the LNA/mixer resonator in place, and does not include the IF filter insertion loss. _______________________________________________________________________________________ 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver SUPPLY CURRENT vs. RF FREQUENCY 6.8 +25°C +125°C 7.6 +85°C 7.4 7.2 7.0 6.8 6.6 +25°C 6.4 -40°C +105°C 12 10 DEEP-SLEEP CURRENT (µA) 7.2 6.4 7.8 SUPPLY CURRENT (mA) +85°C 7.6 SUPPLY CURRENT (mA) +125°C MAX1471 toc02 +105°C 8.0 MAX1471 toc01 8.0 DEEP-SLEEP CURRENT vs. TEMPERATURE MAX1471 toc03 SUPPLY CURRENT vs. SUPPLY VOLTAGE -40°C 8 6 4 2 6.2 6.0 6.0 2.4 3.3 325 350 375 400 425 450 -40 -15 10 35 60 85 110 TEMPERATURE (°C) BIT-ERROR RATE vs. AVERAGE INPUT POWER (ASK DATA) BIT-ERROR RATE vs. AVERAGE INPUT POWER (FSK DATA) SENSITIVITY vs. TEMPERATURE (ASK DATA) 100 280kHz IF BW FREQUENCY DEVIATION = ±50kHz 1 0.2% BER 0.1 fRF = 315MHz 0.01 fRF = 315MHz -115 -113 -111 -110 -108 AVERAGE INPUT POWER (dBm) SENSITIVITY vs. TEMPERATURE (FSK DATA) SENSITIVITY vs. FREQUENCY DEVIATION (FSK DATA) fRF = 434MHz -108 -15 10 35 60 TEMPERATURE (°C) 85 110 10 35 60 85 110 RSSI vs. RF INPUT POWER 1.6 AGC HYSTERESIS: 3dB 1.4 1.2 -102 HIGH-GAIN MODE AGC SWITCH POINT 1.0 -104 -106 0.8 0.6 -108 0.4 0.2 -112 -40 -15 TEMPERATURE (°C) -110 -112 fRF = 315MHz -40 MAX1471 toc08 280kHz IF BW 0.2% BER -100 -105 fRF = 315MHz -110 fRF = 434MHz -114 RSSI (V) -106 -98 SENSITIVITY (dBm) -104 -113 AVERAGE INPUT POWER (dBm) 280kHz IF BW 0.2% BER FREQUENCY DEVIATION = ±50kHz -111 -120 -115 MAX1471 toc07 -102 -117 -108 -117 0.01 -119 280kHz IF BW 0.2% BER MAX1471 toc09 0.2% BER fRF = 434MHz SENSITIVITY (dBm) BIT-ERROR RATE 1 -121 -105 10 fRF = 434MHz -123 -102 MAX1471 toc05 280kHz IF BW MAX1471 toc06 RF FREQUENCY (MHz) 0.1 SENSITIVITY (dBm) 0 300 3.6 SUPPLY VOLTAGE (V) 10 BIT-ERROR RATE (%) 3.0 MAX1471 toc04 100 2.7 LOW-GAIN MODE 0 1 10 FREQUENCY DEVIATION (kHz) 100 -130 -110 -90 -70 -50 -30 RF INPUT POWER (dBm) -10 _______________________________________________________________________________________ 10 5 MAX1471 Typical Operating Characteristics (Typical Application Circuit, VAVDD = VDVDD = VHVIN = +3.0V, fRF = 434MHz, TA = +25°C, unless otherwise noted.) MAX1471 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver Typical Operating Characteristics (continued) (Typical Application Circuit, VAVDD = VDVDD = VHVIN = +3.0V, fRF = 434MHz, TA = +25°C, unless otherwise noted.) 1.2 0.5 0.9 -0.5 0.6 -1.5 DELTA 0.3 1.6 1.2 0.8 0.4 -70 -50 -30 -10 10.4 10 IMAGE REJECTION vs. TEMPERATURE 10.5 10.6 10.7 10.8 10.9 NORMALIZED IF GAIN (dBm) 44 fRF = 434MHz 42 40 5 10 20 25 30 S11 LOG-MAGNITUDE PLOT WITH MATCHING NETWORK OF RFIN (434MHz) MAX1471 toc14 0 10dB/ div -5 0dB 0dB -10 -15 434MHz -16.4dB -20 38 -40 -15 10 35 60 TEMPERATURE (°C) 85 110 1 10 100 START: 50MHz IF FREQUENCY (MHz) S11 SMITH CHART OF RFIN (434MHz) MAX1471 toc16 500MHz 200MHz 6 15 IF FREQUENCY (MHz) 5 MAX1471 toc13 fRF = 315MHz LOWER SIDEBAND 0 11.0 NORMALIZED IF GAIN vs. IF FREQUENCY 48 IMAGE REJECTION (dB) 10 IF FREQUENCY (MHz) RF INPUT POWER (dBm) 46 20 FROM RFIN TO MIXOUT fRF = 434MHz -10 0 -3.5 -90 45dB IMAGE REJECTION 30 0 -2.5 0 40 MAX1471 toc15 1.5 DELTA (%) RSSI (V) RSSI 1.5 UPPER SIDEBAND 50 SYSTEM GAIN (dB) 2.5 FSK DEMODULATOR OUTPUT (V) 1.8 60 MAX1471 toc12 2.0 3.5 MAX1471 toc11 MAX1471 toc10 2.1 SYSTEM VOLTAGE GAIN vs. IF FREQUENCY FSK DEMODULATOR OUTPUT vs. IF FREQUENCY RSSI AND DELTA vs. IF INPUT POWER _______________________________________________________________________________________ STOP: 1GHz 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver INPUT IMPEDANCE vs. INDUCTIVE DEGENERATION MAX1471 toc17 fRF = 315MHz L1 = 0nH REAL IMPEDANCE (Ω) -200 60 IMAGINARY IMPEDANCE 50 -225 40 -250 30 -275 -300 20 10 0 10 1 -175 -200 60 IMAGINARY IMPEDANCE 50 -250 -275 30 REAL IMPEDANCE 20 10 -350 100 0 INDUCTIVE DEGENERATION (nH) -70 -80 -90 -100 -110 fRF = 434MHz -60 PHASE NOISE (dBc/Hz) PHASE NOISE (dBc/Hz) PHASE NOISE vs. OFFSET FREQUENCY -50 MAX1471 toc19 fRF = 315MHz -350 100 10 1 PHASE NOISE vs. OFFSET FREQUENCY -60 -300 -325 INDUCTIVE DEGENERATION (nH) -50 -225 40 -325 REAL IMPEDANCE -125 -150 70 REAL IMPEDANCE (Ω) -175 70 fRF = 434MHz L1 = 0nH 80 -150 IMAGINARY IMPEDANCE (Ω) 80 MAX1471 toc18 90 -125 MAX1471 toc20 90 IMAGINARY IMPEDANCE (Ω) INPUT IMPEDANCE vs. INDUCTIVE DEGENERATION -70 -80 -90 -100 -110 -120 -120 100 1k 10k 100k 1M 10M 100 OFFSET FREQUENCY (Hz) 1k 10k 1M 100k 10M OFFSET FREQUENCY (Hz) Pin Description PIN NAME FUNCTION 1 DSA- Inverting Data Slicer Input for ASK Data 2 DSA+ Noninverting Data Slicer Input for ASK Data 3 OPA+ Noninverting Op-Amp Input for the ASK Sallen-Key Data Filter 4 DFA 5 XTAL2 Data-Filter Feedback Node. Input for the feedback of the ASK Sallen-Key data filter. 2nd Crystal Input _______________________________________________________________________________________ 7 MAX1471 Typical Operating Characteristics (continued) (Typical Application Circuit, VAVDD = VDVDD = VHVIN = +3.0V, fRF = 434MHz, TA = +25°C, unless otherwise noted.) 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 Pin Description (continued) 8 PIN NAME FUNCTION 6 XTAL1 1st Crystal Input 7 AVDD Analog Power-Supply Voltage for RF Sections. AVDD is connected to an on-chip +3.0V low-dropout regulator. Decouple to AGND with a 0.1µF capacitor. 8 LNAIN Low-Noise Amplifier Input 9 LNASRC Low-Noise Amplifier Source for External Inductive Degeneration. Connect an inductor to AGND to set LNA input impedance. 10 LNAOUT Low-Noise Amplifier Output. Connect to mixer through an LC tank filter. 11 MIXIN+ Differential Mixer Input. Must be AC-coupled to driving input. 12 MIXIN- Differential Mixer Input. Bypass to AGND with a capacitor. 13 MIXOUT 14 AGND 15 IFIN- Differential 330Ω IF Limiter Amplifier Input. Bypass to AGND with a capacitor. 16 IFIN+ Differential 330Ω IF Limiter Amplifier Input. Connect to output of the 10.7MHz IF filter. 17 PDMINF Minimum-Level Peak Detector for FSK Data 18 PDMAXF Maximum-Level Peak Detector for FSK Data 19 DSF- Inverting Data Slicer Input for FSK Data 20 DSF+ Noninverting Data Slicer Input for FSK Data 21 OPF+ Noninverting Op-Amp Input for the FSK Sallen-Key Data Filter 22 DFF 23 DGND Digital Ground 24 DVDD Digital Power-Supply Voltage for Digital Sections. Connect to AVDD. Decouple to DGND with a 10nF capacitor. 25 FDATA Digital Baseband FSK Demodulator Data Output 26 CS Active-Low Chip-Select Input 27 DIO Serial Data Input/Output 28 SCLK Serial Interface Clock Input 29 HVIN High-Voltage Supply Input. For 3V operation, connect HVIN to AVDD and DVDD. 30 ADATA Digital Baseband ASK Demod Data Output 31 PDMINA Minimum-Level Peak Detector for ASK Output 32 PDMAXA Maximum-Level Peak Detector for ASK Output — EP 330Ω Mixer Output. Connect to the input of the 10.7MHz IF filter. Analog Ground Data-Filter Feedback Node. Input for the feedback of the FSK Sallen-Key data filter. Exposed Pad. Connect to ground. _______________________________________________________________________________________ 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver LNAIN 8 LNASRC 9 LNAOUT MIXIN+ MIXIN- 10 11 12 MIXOUT IFIN13 IFIN+ 15 16 IMAGE REJECTION 0° LNA IF LIMITING AMPS Σ 90° RSSI AGND 14 XTAL1 6 XTAL2 5 CRYSTAL OSCILLATOR DIVIDE BY 32 VCO PHASE DETECTOR LOOP FILTER RDF1 100kΩ 4 DFA 3 OPA+ 2 DSA+ RDF2 100kΩ CS 26 FSK SERIAL INTERFACE, CONTROL REGISTERS, AND POLLING TIMER DIO 27 ASK FSK DEMODULATOR ASK DATA FILTER SCLK 28 DVDD 24 31 PDMINA DGND 23 RDF1 100kΩ RDF2 100kΩ 32 PDMAXA 1 DSA- FSK DATA FILTER HVIN 29 AVDD 7 30 ADATA 3.0V REG 3.0V MAX1471 25 19 18 17 20 21 22 FDATA DSF- PDMAXF PDMINF DSF+ OPF+ DFF _______________________________________________________________________________________ 9 MAX1471 Functional Diagram MAX1471 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver Detailed Description The MAX1471 CMOS superheterodyne receiver and a few external components provide a complete ASK/FSK receive chain from the antenna to the digital output data. Depending on signal power and component selection, data rates as high as 33kbps using Manchester Code (66kbps nonreturn to zero) can be achieved. The MAX1471 is designed to receive binary FSK or ASK data on a 300MHz to 450MHz carrier. ASK modulation uses a difference in amplitude of the carrier to represent logic 0 and logic 1 data. FSK uses the difference in frequency of the carrier to represent a logic 0 and logic 1. Low-Noise Amplifier (LNA) The LNA is a cascode amplifier with off-chip inductive degeneration that achieves approximately 28dB of voltage gain that is dependent on both the antenna-matching network at the LNA input, and the LC tank network between the LNA output and the mixer inputs. The off-chip inductive degeneration is achieved by connecting an inductor from LNASRC to AGND. This inductor sets the real part of the input impedance at LNAIN, allowing for a flexible match to low input impedances such as a PCB trace antenna. A nominal value for this inductor with a 50Ω input impedance is 15nH at 315MHz and 10nH at 434MHz, but the inductance is affected by PCB trace length. See the Typical Operating Characteristics to see the relationship between the inductance and input impedance. The inductor can be shorted to ground to increase sensitivity by approximately 1dB, but the input match is not optimized for 50Ω. The LC tank filter connected to LNAOUT comprises L2 and C9 (see the Typical Application Circuit). Select L2 and C9 to resonate at the desired RF input frequency. The resonant frequency is given by: f= 1 2π L TOTAL × CTOTAL where LTOTAL = L2 + LPARASITICS and CTOTAL = C9 + CPARASITICS. LPARASITICS and CPARASITICS include inductance and capacitance of the PCB traces, package pins, mixer input impedance, LNA output impedance, etc. These parasitics at high frequencies cannot be ignored, and can have a dramatic effect on the tank filter center frequency. Lab experimentation should be done to optimize the center frequency of the tank. 10 Automatic Gain Control (AGC) When the AGC is enabled, it monitors the RSSI output. When the RSSI output reaches 1.28V, which corresponds to an RF input level of approximately -64dBm, the AGC switches on the LNA gain reduction attenuator. The attenuator reduces the LNA gain by 35dB, thereby reducing the RSSI output by about 0.55V. The LNA resumes high-gain mode when the RSSI output level drops back below 0.68V (approximately -67dBm at the RF input) for a programmable interval called the AGC dwell time. The AGC has a hysteresis of approximately 3dB. With the AGC function, the RSSI dynamic range is increased, allowing the MAX1471 to reliably produce an ASK output for RF input levels up to 0dBm with a modulation depth of 18dB. AGC is not necessary and can be disabled when utilizing only the FSK data path. The MAX1471 features an AGC lock controlled by the AGC lock bit (see Table 8). When the bit is set, the LNA is locked in its present gain state. Mixer A unique feature of the MAX1471 is the integrated image rejection of the mixer. This device was designed to eliminate the need for a costly front-end SAW filter for many applications. The advantage of not using a SAW filter is increased sensitivity, simplified antenna matching, less board space, and lower cost. The mixer cell is a pair of double-balanced mixers that perform an IQ downconversion of the RF input to the 10.7MHz intermediate frequency (IF) with low-side injection (i.e., fLO = fRF - fIF). The image-rejection circuit then combines these signals to achieve approximately 45dB of image rejection. Low-side injection is required as high-side injection is not possible due to the on-chip image rejection. The IF output is driven by a source follower, biased to create a driving impedance of 330Ω to interface with an off-chip 330Ω ceramic IF filter. The voltage conversion gain driving a 330Ω load is approximately 19.5dB. Note that the MIXIN+ and MIXIN- inputs are functionally identical. Phase-Locked Loop (PLL) The PLL block contains a phase detector, charge pump/integrated loop filter, voltage-controlled oscillator (VCO), asynchronous 32x clock divider, and crystal oscillator. This PLL does not require any external components. The relationship between the RF, IF, and reference frequencies is given by: fREF = (fRF - fIF)/32 To allow the smallest possible IF bandwidth (for best sensitivity), the tolerance of the reference must be minimized. ______________________________________________________________________________________ 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver FSK Demodulator The FSK demodulator uses an integrated 10.7MHz PLL that tracks the input RF modulation and determines the difference between frequencies as logic-level ones and zeros. The PLL is illustrated in Figure 1. The input to the PLL comes from the output of the IF limiting amplifiers. The PLL control voltage responds to changes in the frequency of the input signal with a nominal gain of 2.2mV/kHz. For example, an FSK peak-to-peak deviation of 50kHz generates a 110mVP-P signal on the control line. This control line is then filtered and sliced by the FSK baseband circuitry. The FSK demodulator PLL requires calibration to overcome variations in process, voltage, and temperature. For more information on calibrating the FSK demodulator, see the Calibration section. The maximum calibration time is 120µs. In DRX mode, the FSK demodulator calibration occurs automatically just before the IC enters sleep mode. Crystal Oscillator The XTAL oscillator in the MAX1471 is used to generate the local oscillator (LO) for mixing with the received signal. The XTAL oscillator frequency sets the received signal frequency as: fRECEIVE = (fXTAL x 32) +10.7MHz The received image frequency at: fIMAGE = (fXTAL x 32) -10.7MHz is suppressed by the integrated quadrature imagerejection circuitry. For an input RF frequency of 315MHz, a reference frequency of 9.509MHz is needed for a 10.7MHz IF frequency (low-side injection is required). For an input RF frequency of 433.92MHz, a reference frequency of 13.2256MHz is required. The XTAL oscillator in the MAX1471 is designed to present a capacitance of approximately 3pF between the XTAL1 and XTAL2. If a crystal designed to oscillate with a different load capacitance is used, the crystal is pulled away from its stated operating frequency, introducing an error in the reference frequency. Crystals designed to operate with higher differential load capacitance always pull the reference frequency higher. In actuality, the oscillator pulls every crystal. The crystal’s natural frequency is really below its specified frequency, but when loaded with the specified load capacitance, the crystal is pulled and oscillates at its specified frequency. This pulling is already accounted for in the specification of the load capacitance. Additional pulling can be calculated if the electrical parameters of the crystal are known. The frequency pulling is given by: fp = ⎞ Cm ⎛ 1 1 6 − ⎜ ⎟ × 10 2 ⎝ Ccase + Cload Ccase + Cspec ⎠ where: fp is the amount the crystal frequency pulled in ppm. Cm is the motional capacitance of the crystal. Ccase is the case capacitance. Cspec is the specified load capacitance. Cload is the actual load capacitance. When the crystal is loaded as specified, i.e., Cload = Cspec, the frequency pulling equals zero. TO FSK BASEBAND FILTER AND DATA SLICER IF LIMITING AMPS PHASE DETECTOR CHARGE PUMP LOOP FILTER 10.7MHz VCO 2.2mV/kHz Figure 1. FSK Demodulator PLL Block Diagram ______________________________________________________________________________________ 11 MAX1471 Intermediate Frequency (IF) The IF section presents a differential 330Ω load to provide matching for the off-chip ceramic filter. It contains five AC-coupled limiting amplifiers with a bandpass-filter-type response centered near the 10.7MHz IF frequency with a 3dB bandwidth of approximately 10MHz. For ASK data, the RSSI circuit demodulates the IF to baseband by producing a DC output proportional to the log of the IF signal level with a slope of approximately 16mV/dB. For FSK, the limiter output is fed into a PLL to demodulate the IF. MAX1471 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver ASK DATA OUT VDD 3.0V SCLK DIO VDD C26 CS FSK DATA OUT 26 25 CS DIO 27 SLCK HVIN 28 VDD FDATA C5 29 ADATA DSA- 30 PDMINA 1 31 PDMAXA 32 DVDD 24 R3 2 3 C4 C23 VCC DGND DSA+ OPA+ C3 DFF 4 DFA OPF+ C14 5 Y1 VDD C15 6 7 C22 C21 DSF+ XTAL1 AVDD DSF- C7 9 10 11 12 C11 13 C8 C9 L3 14 IFIN- 15 IFIN+ PDMAXF AGND MIXOUT MIXIN- MIXIN+ LNAIN LNAOUT 8 21 XTAL2 LNASRC RF INPUT 22 MAX1471 C6 L1 23 PDMINF 20 R8 19 C27 18 17 16 C12 VDD L2 IN GND C10 OUT Y2 Figure 2. Typical Application Circuit Data Filters The data filters for the ASK and FSK data are implemented as a 2nd-order lowpass Sallen-Key filter. The pole locations are set by the combination of two onchip resistors and two external capacitors. Adjusting the value of the external capacitors changes the corner frequency to optimize for different data rates. The corner frequency in kHz should be set to approximately 1.5 times the fastest expected Manchester data rate in kbps from the transmitter. Keeping the corner frequency near the data rate rejects any noise at higher frequencies, resulting in an increase in receiver sensitivity. The configuration shown in Figure 3 can create a Butterworth or Bessel response. The Butterworth filter offers a very flat amplitude response in the passband 12 and a rolloff rate of 40dB/decade for the two-pole filter. The Bessel filter has a linear phase response, which works well for filtering digital data. To calculate the value of the capacitors, use the following equations, along with the coefficients in Table 2: CF1 = b a(100k)( π)(fC ) CF2 = a 4(100k)( π)(fC ) where fC is the desired 3dB corner frequency. For example, choose a Butterworth filter response with a corner frequency of 5kHz: ______________________________________________________________________________________ 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 Table 1. Component Values for Typical Application Circuit COMPONENT VALUE FOR 433.92MHz RF VALUE FOR 315MHz RF DESCRIPTION (%) C3 220pF 220pF 10 C4 470pF 470pF 5 C5 0.047µF 0.047µF 10 C6 0.1µF 0.1µF 10 C7 100pF 100pF 5 C8 100pF 100pF 5 C9 1.0pF 2.2pF ±0.1pF C10 220pF 220pF 10 C11 100pF 100pF 5 C12 1500pF 1500pF 10 C14 15pF 15pF 5 C15 15pF 15pF 5 10 C21 220pF 220pF C22 470pF 470pF 5 C23 0.01µF 0.01µF 10 C26 0.1µF 0.1µF 10 C27 0.047µF 0.047µF 10 L1 56nH 100nH Coilcraft 0603CS L2 16nH 30nH Coilcraft 0603CS L3 10nH 15nH 5 R3 25kΩ 25kΩ 5 R8 25kΩ 25kΩ 5 Y1 13.2256MHz 9.509MHz Crystal Y2 10.7MHz ceramic filter 10.7MHz ceramic filter Murata SFECV10.7 series Note: Component values vary depending on PCB layout. 1.000 CF1 = ≈ 450pF (1.414)(100kΩ)(3.14)(5kHz) CF2 = 1.414 ≈ 225pF (4)(100kΩ)(3.14)(5kHz) Choosing standard capacitor values changes CF1 to 470pF and CF2 to 220pF. In the Typical Application Circuit, CF1 and CF2 are named C4 and C3, respectively, for ASK data, and C21 and C22 for FSK data. Data Slicers The purpose of a data slicer is to take the analog output of a data filter and convert it to a digital signal. This is achieved by using a comparator and comparing the analog input to a threshold voltage. The threshold voltage is set by the voltage on the DSA- pin for the ASK receive chain (DSF- for the FSK receive chain), which is connected to the negative input of the data slicer comparator. Numerous configurations can be used to generate the data-slicer threshold. For example, the circuit in Figure 4 shows a simple method using only one resistor and one capacitor. This configuration averages the analog output of the filter and sets the threshold to approximately 50% of that amplitude. With this configuration, the threshold automatically adjusts as the analog signal varies, minimizing the possibility for errors in the digital data. The sizes of R and C affect how fast the threshold tracks to the analog amplitude. Be sure to keep the corner frequency of the RC circuit much lower than the lowest expected data rate. ______________________________________________________________________________________ 13 MAX1471 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver Table 2. Coefficients to Calculate CF1 and CF2 FILTER TYPE a b Butterworth (Q = 0.707) 1.414 1.000 Bessel (Q = 0.577) 1.3617 0.618 MAX1471 RSSI OR FSK DEMOD 100kΩ DSA+ DSF+ OPA+ OPF+ 100kΩ DFA DFF CF2 CF1 Figure 3. Sallen-Key Lowpass Data Filter MAX1471 DATA SLICER ADATA FDATA DSADSFC DSA+ DSF+ R Figure 4. Generating Data-Slicer Threshold Using a Lowpass Filter With this configuration, a long string of NRZ zeros or ones can cause the threshold to drift. This configuration works best if a coding scheme, such as Manchester coding, which has an equal number of zeros and ones, is used. 14 Figure 5 shows a configuration that uses the positive and negative peak detectors to generate the threshold. This configuration sets the threshold to the midpoint between a high output and a low output of the data filter. Peak Detectors The maximum peak detectors (PDMAXA for ASK, PDMAXF for FSK) and minimum peak detectors (PDMINA for ASK, PDMINF for FSK), in conjunction with resistors and capacitors shown in Figure 5, create DC output voltages proportional to the high and low peak values of the filtered ASK or FSK demodulated signals. The resistors provide a path for the capacitors to discharge, allowing the peak detectors to dynamically follow peak changes of the data-filter output voltages. The maximum and minimum peak detectors can be used together to form a data-slicer threshold voltage at a midvalue between the maximum and minimum voltage levels of the data stream (see the Data Slicers section and Figure 5). The RC time constant of the peakdetector combining network should be set to at least 5 times the data period. If there is an event that causes a significant change in the magnitude of the baseband signal, such as an AGC gain switch or a power-up transient, the peak detectors may “catch” a false level. If a false peak is detected, the slicing level is incorrect. The MAX1471 has a feature called peak-detector track enable (TRK_EN), where the peak-detector outputs can be reset (see Figure 6). If TRK_EN is set (logic 1), both the maximum and minimum peak detectors follow the input signal. When TRK_EN is cleared (logic 0), the peak detectors revert to their normal operating mode. The TRK_EN function is automatically enabled for a short time and then disabled whenever the IC recovers from the sleep portion of DRX mode, or when an AGC gain switch occurs. Since the peak detectors exhibit a fast attack/slow decay response, this feature allows for an extremely fast startup or AGC recovery. See Figure 7 for an illustration of a fast-recovery sequence. In addition to the automatic control of this function, the TRK_EN bits can be controlled through the serial interface (see the Serial Control Interface section). Power-Supply Connections The MAX1471 can be powered from a 2.4V to 3.6V supply or a 4.5V to 5.5V supply. The device has an on-chip linear regulator that reduces the 5V supply to 3V needed to operate the chip. To operate the MAX1471 from a 3V supply, connect DVDD, AVDD, and HVIN to the 3V supply. When using a 5V supply, connect the supply to HVIN only and con- ______________________________________________________________________________________ 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 MAX1471 DATA SLICER MAXIMUM PEAK DETECTOR PDMAXA PDMAXF C ADATA FDATA MINIMUM PEAK DETECTOR R PDMINA PDMINF R C Figure 5. Generating Data-Slicer Threshold Using the Peak Detectors MINIMUM PEAK DETECTOR PDMINA PDMINF BASEBAND FILTER TRK_EN = 1 TO SLICER INPUT MAXIMUM PEAK DETECTOR PDMAXA PDMAXF MAX1471 TRK_EN = 1 Figure 6. Peak-Detector Track Enable nect AVDD and DVDD together. In both cases, bypass DVDD and HVIN with a 0.01µF capacitor and AVDD with a 0.1µF capacitor. Place all bypass capacitors as close as possible to the respective supply pin. ______________________________________________________________________________________ 15 MAX1471 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver Serial Control Interface Communication Protocol The MAX1471 can use a 4-wire interface or a 3-wire interface (default). In both cases, the data input must follow the timing diagrams shown in Figures 8 and 9. Note that the DIO line must be held LOW while CS is high. This is to prevent the MAX1471 from entering discontinuous receive mode if the DRX bit is high. The data is latched on the rising edge of SCLK, and therefore must be stable before that edge. The data sequencing is MSB first, the command (C[3:0]; see Table 3), the register address (A[3:0]; see Table 4) and the data (D[7:0]; see Table 5). The mode of operation (3-wire or 4-wire interface) is selected by DOUT_FSK and/or DOUT_ASK bits in the configuration register. Either of those bits selects the ASKOUT and/or FSKOUT line as a SERIAL data output. Upon receiving a read register command (0x2), the serial interface outputs the data on either pin, according to Figure 10. RECEIVER ENABLED, TRK_EN SET TRK_EN CLEARED MAX PEAK DETECTOR 200mV/div FILTER OUTPUT MIN PEAK DETECTOR DATA OUTPUT DATA OUTPUT 2V/div 100µs/div Figure 7. Fast Receiver Recovery in FSK Mode Utilizing Peak Detectors would do. The reset signal remains active for as long as CS is high after the command is sent. Continuous Receive Mode (DRX = 0) In continuous receive mode, individual analog modules can be powered on directly through the power configuration register (register 0x0). The SLEEP bit (bit 0) overrides the power settings of the remaining bits and puts the part into deep-sleep mode when set. It is also necessary to write the frequency divisor of the external crystal in the oscillator frequency register (register 0x3) to optimize image rejection and to enable accurate calibration sequences for the polling timer and the FSK demodulator. This number is the integer result of fXTAL/100kHz. If the FSK receive function is selected, it is necessary to perform an FSK calibration to improve receive sensitivity. Polling timer calibration is not necessary. See the Calibration section for more information. If neither of these bits are 1, the 3-wire interface is selected (default on power-up) and the DIO line is effectively a bidirectional input/output line. DIO is selected as an output of the MAX1471 for the following CS cycle whenever a READ command is received. The CPU must tri-state the DIO line on the cycle of CS that follows a read command, so the MAX1471 can drive the data output line. Figure 11 shows the diagram of the 3-wire interface. Note that the user can choose to send either 16 cycles of SCLK, as in the case of the 4wire interface, or just eight cycles, as all the registers are 8-bits wide. The user must drive DIO low at the end of the read sequence. The MASTER RESET command (0x3) (see Table 3) sends a reset signal to all the internal registers of the MAX1471 just like a power-off and power-on sequence tCS tCSI CS tCSS tCH tSC tCSH tCL SCLK tDO tDH tDI DIO tTR tDV HIGH-IMPEDANCE HIGH-IMPEDANCE DATA IN D7 D0 DATA OUT Figure 8. Digital Communications Timing Diagram 16 ______________________________________________________________________________________ HI-Z 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 CS SCLK DIO C3 C2 C1 C0 A3 A2 A1 A0 D7 D6 D5 D4 D2 D1 D0 DATA ADDRESS COMMAND D3 Figure 9. Data Input Diagram CS SCLK DIO 0 0 1 READ COMMAND 0 A3 A2 A1 A0 0 0 0 ADDRESS 0 0 0 0 0 C3 C1 C0 A3 R7 R6 R5 A2 A1 A0 D7 ADDRESS COMMAND DATA ADATA (IF DOUT_ASK = 1) C2 R4 R3 R2 R1 DATA R0 R7 R7 R6 R5 R4 R3 REGISTER DATA R0 REGISTER DATA REGISTER DATA FDATA (IF DOUT_FSK = 1) D0 R2 R1 R0 R7 R0 REGISTER DATA Figure 10. Read Command on a 4-Wire SERIAL Interface Discontinuous Receive Mode (DRX = 1) In the discontinuous receive mode (DRX = 1), the power signals of the different modules of the MAX1471 toggle between OFF and ON, according to internal timers tOFF, tCPU, and tRF. It is also necessary to write the frequency divisor of the external crystal in the oscillator frequency register (register 0x3). This number is the integer result of fXTAL/100kHz. Before entering the discontinuous receive mode for the first time, it is also necessary to calibrate the timers (see the Calibration section). The MAX1471 uses a series of internal timers (tOFF, t CPU , and t RF ) to control its power-up. The timer sequence begins when both CS and DIO are one. The MAX1471 has an internal pullup on the DIO pin, so the user must tri-state the DIO line when CS goes high. The external CPU can then go to a sleep mode during tOFF. A high-to-low transition on DIO, or a low level on DIO serves as the wake-up signal for the CPU, which must then start its wake-up procedure, and drive DIO low before tLOW expires (tCPU + tRF). Once tRF expires, the MAX1471 enables the FSKOUT and/or ASKOUT data outputs. The CPU must then keep DIO low for as long as it may need to analyze any received data. Releasing DIO causes the MAX1471 to pull up DIO, reinitiating the tOFF timer. Oscillator Frequency Register (Address: 0x3) The MAX1471 has an internal frequency divider that divides down the crystal frequency to 100kHz. The MAX1471 uses the 100kHz clock signal when calibrating itself and also to set the image-rejection frequency. The hexadecimal value written to the oscillator frequency register is the nearest integer result of fXTAL/100kHz. ______________________________________________________________________________________ 17 MAX1471 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver CS SCLK DIO 0 0 1 0 A3 READ COMMAND A2 A1 A0 0 0 0 0 ADDRESS 0 0 0 0 R7 R6 R5 DATA R4 R3 R2 R1 R0 R7 R0 REGISTER DATA REGISTER DATA 16 BITS OF DATA CS SCLK DIO 0 0 1 READ COMMAND 0 A3 A2 A1 A0 0 0 0 ADDRESS 0 0 DATA 0 0 0 R7 R6 R5 R4 R3 R2 R1 A3 REGISTER DATA 8 BITS OF DATA Figure 11. Read Command in 3-Wire Interface ister. To calculate the dwell time, use the following equation: Table 3. Command Bits C[3:0] DESCRIPTION 0x0 No operation 0x1 Write data 0x2 Read data 0x3 Master reset 0x4–0xF Not used For example, if data is being received at 315MHz, the crystal frequency is 9.509375MHz. Dividing the crystal frequency by 100kHz and rounding to the nearest integer gives 95, or 0x5F hex. So for 315MHz, 0x5F would be written to the oscillator frequency register. AGC Dwell Timer Register (Address: 0xA) The AGC dwell timer holds the AGC in low-gain state for a set amount of time after the power level drops below the AGC switching threshold. After that set amount of time, if the power level is still below the AGC threshold, the LNA goes into high-gain state. This is important for ASK since the modulated data may have a high level above the threshold and a low level below the threshold, which without the dwell timer would cause the AGC to switch on every bit. The AGC dwell time is dependent on the crystal frequency and the bit settings of the AGC dwell timer reg- 18 Dwell Time = 2Reg0xA fXTAL where Reg 0xA is the value of register 0xA in decimal. To calculate the value to write to register 0xA, use the following equation and use the next integer higher than the calculated result: Reg 0xA ≥ 3.3 x log10 (Dwell Time x fXTAL) For Manchester Code (50% duty cycle), set the dwell time to at least twice the bit period. For nonreturn-tozero (NRZ) data, set the dwell to greater than the period of the longest string of zeros or ones. For example, using Manchester code at 315MHz (f XTAL = 9.509375MHz) with a data rate of 4kbps (bit period = 125µs), the dwell time needs to be greater than 250µs: Reg 0xA ≥ 3.3 x log10 (250µs x 9.509375MHz) ≈11.14 Choose the register value to be the next integer value higher than 11.14, which is 12 or 0x0C hex. The default value of the AGC dwell timer on power-up or reset is 0x0D. ______________________________________________________________________________________ 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver REGISTER A[3:0] REGISTER NAME 0x0 Power configuration 0x1 Configuration Sets options for the device such as output enables, off-timer prescale, and discontinuous receive mode (see Table 7). 0x2 Control Controls AGC lock, peak-detector tracking, as well as polling timer and FSK calibration (see Table 8). 0x3 Oscillator frequency 0x4 Off timer—tOFF (upper byte) 0x5 Off timer—tOFF (lower byte) 0x6 CPU recovery timer—tCPU 0x7 RF settle timer—tRF (upper byte) 0x8 RF settle timer—tRF (lower byte) 0x9 Status register (read only) 0xA AGC dwell timer DESCRIPTION Enables/disables the LNA, AGC, mixer, baseband, peak detectors, and sleep mode (see Table 6). Sets the internal clock frequency divisor. This register must be set to the integer result of fXTAL/100kHz (see the Oscillator Frequency Register section). Sets the duration that the MAX1471 remains in low-power mode when DRX is active (see Table 10). Increases maximum time the MAX1471 stays in lower power mode while CPU wakes up when DRX is active (see Table 11). During the time set by the settle timer, the MAX1471 is powered on with the peak detectors and the data outputs disabled to allow time for the RF section to settle. DIO must be driven low at any time during tLOW = tCPU + tRF or the timer sequence restarts (see Table 12). Provides status for PLL lock, AGC state, crystal operation, polling timer, and FSK calibration (see Table 9). Controls the dwell (release) time of the AGC. Calibration The MAX1471 must be calibrated to ensure accurate timing of the off timer in discontinuous receive mode or when receiving FSK signals. The first step in calibration is ensuring that the oscillator frequency register (address: 0x3) has been programmed with the correct divisor value (see the Oscillator Frequency Register section). Next, enable the mixer to turn the crystal driver on. Calibrate the polling timer by setting POL_CAL_EN = 1 in the configuration register (register 0x1). Upon completion, the POL_CAL_DONE bit in the status register (register 0x8) is 1, and the POL_CAL_EN bit is reset to zero. If using the MAX1471 in continuous receive mode, polling timer calibration is not needed. FSK receiver calibration is a two-step process. Set FSKCALLSB = 1 (register 0x1) or to reduce the calibration time, accuracy can be sacrificed by setting the FSKCALLSB = 0. Next, initiate FSK receiver calibration, set FSK_CAL_EN = 1. Upon completion, the FSK_CAL_DONE bit in the status register (register 0x8) is one, and the FSK_CAL_EN bit is reset to zero. When in continuous receive mode and receiving FSK data, recalibrate the FSK receiver after a significant change in temperature or supply voltage. When in discontinuous receive mode, the polling timer and FSK receiver (if enabled) are automatically calibrated during every wake-up cycle. Off Timer (tOFF) The first timer, tOFF (see Figure 12), is a 16-bit timer that is configured using: register 0x4 for the upper byte, register 0x5 for the lower byte, and bits PRESCALE1 and PRESCALE0 in the configuration register (register 0x1). Table 10 summarizes the configuration of the tOFF timer. The PRESCALE1 and PRESCALE2 bits set the size of the shortest time possible (tOFF time base). The data written to the tOFF registers (0x4 and 0x5) is multiplied by the time base to give the total tOFF time. On power-up, the off timer registers are set to zero and must be written before using DRX mode. ______________________________________________________________________________________ 19 MAX1471 Table 4. Register Summary MAX1471 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver Table 5. Register Configuration ADDRESS A3 A2 A1 A0 DATA D7 D6 D5 D4 D3 LNA_EN AGC_EN MIXER_ EN FSKBB_ EN FSKPD_ EN X GAIN SET* FSKCALL SB FSK_ DOUT ASK_ DOUT X AGC LOCK X X d7 d6 d5 d4 d3 t15 t14 t13 t12 t7 t6 t5 t7 t6 t15 D2 D1 D0 POWER CONFIGURATION (0x0) 0000 ASKBB_ EN ASKPD_ EN SLEEP TOFF_ PS1 TOFF_ PS0 DRX_ MODE POL_ CAL_EN FSK_CAL _EN d2 d1 d0 t11 t10 t9 t8 t4 t3 t2 t1 t0 t5 t4 t3 t2 t1 t0 t14 t13 t12 t11 t10 t9 t8 t7 t6 t5 t4 t3 t2 t1 t0 LOCK DET AGCST CLK ALIVE X X X X X X dt4 dt3* dt2* CONFIGURATION (0x1) 0001 CONTROL (0x2) 0010 FSKTRK_ ASKTRK_ EN EN OSCILLATOR FREQUENCY (0x3) 0011 OFF TIMER (upper byte) (0x4) 0100 OFF TIMER (lower byte) (0x5) 0101 CPU RECOVERY TIMER (0x6) 0110 RF SETTLE TIMER (upper byte) (0x7) 0111 RF SETTLE TIMER (lower byte) (0x8) 1000 STATUS REGISTER (read only) (0x9) 1001 POL_CAL FSK_CAL _DONE _DONE AGC DWELL TIMER (0xA) 1010 dt1 dt0* *Power-up state = 1. All other bits, power-up state = 0. During tOFF, the MAX1471 is operating with very low supply current (5.0µA typ), where all of its modules are turned off, except for the tOFF timer itself. Upon completion of the tOFF time, the MAX1471 signals the user by asserting DIO low. CPU Recovery Timer (tCPU) The second timer, tCPU (see Figure 12), is used to delay the power-up of the MAX1471, thereby providing extra power savings and giving a CPU the time required to complete its own power-on sequence. The CPU is signaled to begin powering up when the DIO line is pulled low by the MAX1471 at the end of tOFF. tCPU then begins 20 counting down, while DIO is held low by the MAX1471. At the end of tCPU, the tRF counter begins. tCPU is an 8-bit timer, configured through register 0x6. The possible tCPU settings are summarized in Table 11. The data written to the tCPU register (0x6) is multiplied by 120µs to give the total tCPU time. On power-up, the CPU timer register is set to zero and must be written before using DRX mode. RF Settle Timer (tRF) The third timer, tRF (see Figure 12), is used to allow the RF sections of the MAX1471 to power up and stabilize before ASK or FSK data is received. tRF begins count- ______________________________________________________________________________________ 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver MAX1471 Table 6. Power Configuration Register (Address: 0x0) BIT ID BIT NAME BIT LOCATION (0 = LSB) POWER-UP STATE LNA_EN LNA enable 7 0 1 = Enable LNA 0 = Disable LNA AGC_EN AGC enable 6 0 1 = Enable AGC 0 = Disable AGC MIXER_EN Mixer enable 5 0 1 = Enable mixer 0 = Disable mixer FSKBB_EN FSK baseband enable 4 0 1 = Enable FSK baseband 0 = Disable FSK baseband FSKPD_EN FSK peak detector enable 3 0 1 = Enable FSK peak detectors 0 = Disable FSK peak detectors ASKBB_EN ASK baseband enable 2 0 1 = Enable ASK baseband 0 = Disable ASK baseband ASKPD_EN ASK peak detector enable 1 0 1 = Enable ASK peak detectors 0 = Disable ASK peak detectors SLEEP Sleep mode 0 0 1 = Deep-sleep mode 0 = Normal operation ing once tCPU has expired. At the beginning of tRF, the modules selected in the power control register (register 0x0) are powered up with the exception of the peak detectors and have the tRF period to settle. At the end of tRF, the MAX1471 stops driving DIO low and enables ADATA, FDATA, and peak detectors if chosen to be active in the power configuration register (0x0). The CPU must be awake at this point, and must hold DIO low for the MAX1471 to remain in operation. The CPU must begin driving DIO low any time during tLOW = tCPU + tRF. If the CPU fails to drive DIO low, DIO is pulled high through the internal pullup resistor, and the timer sequence is restarted, leaving the MAX1471 powered down. Any time the DIO line is driven high while the DRX = 1, the DRX sequence is initiated, as defined in Figure 12. tRF is a 16-bit timer, configured through registers 0x7 (upper byte) and 0x8 (lower byte). The possible tRF settings are in Table 12. The data written to the tRF register (0x7 and 0x8) is multiplied by 120µs to give the total tRF time. On power-up, the RF timer registers are set to zero and must be written before using DRX mode. FUNCTION Typical Power-Up Procedure Here is a typical power-up procedure for receiving either ASK or FSK signals at 315MHz in continuous mode: 1) Write 0x3000 to reset the part. 2) Write 0x10FE to enable all RF and baseband sections. 3) Write 0x135F to set the oscillator frequency register to work with a 315MHz crystal. 4) Write 0x1120 to set FSKCALLSB for an accurate FSK calibration. 5) Write 0x1201 to begin FSK calibration. 6) Read 0x2900 and verify that bit 0 is 1 to indicate FSK calibration is done. The MAX1471 is now ready to receive ASK or FSK data. Due to the high sensitivity of the receiver, it is recommended that the configuration registers be changed only when not receiving data. Receiver desensitization may occur, especially if odd-order harmonics of the SCLK line fall within the IF bandwidth. ______________________________________________________________________________________ 21 MAX1471 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver Table 7. Configuration Register (Address: 0x1) BIT ID BIT NAME BIT LOCATION (0 = LSB) POWER-UP STATE X Don’t care 7 0 Don’t care. 1 0 = LNA low-gain state. 1 = LNA high-gain state. For manual gain control, enable the AGC (AGC_EN = 1), set LNA gain state to desired setting, then disable the AGC (AGC_EN = 0). GAINSET Gain set FSKCALLSB FSK accurate calibration 5 0 FSKCALLSB = 1 enables a longer, more accurate FSK calibration. FSKCALLSB = 0 provides for a quick, less accurate FSK calibration. DOUT_FSK FSKOUT enable 4 0 This bit enables the FDATA pin to act as the serial data output in 4-wire mode. (See the Communication Protocol section.) DOUT_ASK ASKOUT enable 3 0 This bit enables the ADATA pin to act as the serial data output in 4-wire mode. (See the Communication Protocol section.) TOFF_PS1 Off-timer prescale 2 0 TOFF_PS0 Off-timer prescale 1 0 DRX_MODE Receive mode 6 0 Layout Considerations A properly designed PCB is an essential part of any RF/microwave circuit. On high-frequency inputs and outputs, use controlled-impedance lines and keep them as short as possible to minimize losses and radiation. At high frequencies, trace lengths that are on the order of λ/10 or longer act as antennas. Keeping the traces short also reduces parasitic inductance. Generally, 1in of a PCB trace adds about 20nH of parasitic inductance. The parasitic inductance can 22 FUNCTION 0 Sets LSB size for the off timer. (See the Off Timer section.) 1 = Discontinuous receive mode. (See the Discontinuous Receive Mode section.) 0 = Continuous receive mode. (See the Continuous Receive Mode section.) have a dramatic effect on the effective inductance of a passive component. For example, a 0.5in trace connecting a 100nH inductor adds an extra 10nH of inductance or 10%. To reduce the parasitic inductance, use wider traces and a solid ground or power lane below the signal traces. Also, use low-inductance connections to ground on all GND pins, and place decoupling capacitors close to all VDD or HVIN connections. ______________________________________________________________________________________ 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver BIT ID BIT NAME BIT LOCATION (0 = LSB) POWER-UP STATE FUNCTION X None 7 Don’t care AGCLOCK AGC lock 6 0 Don’t care. X None 5, 4 FSKTRK_EN FSK peak detector track enable 3 0 Enables the tracking mode of the FSK peak detectors when FSKTRK_EN = 1. (See the Peak Detectors section.) ASKTRK_EN ASK peak detector track enable 2 0 Enables the tracking mode of the ASK peak detectors when ASKTRK_EN = 1. (See the Peak Detectors section.) Locks the LNA gain in its present state. Don’t care. POL_CAL_EN Polling timer calibration enable 1 0 POL_CAL_EN = 1 starts the polling timer calibration. Calibration of the polling timer is needed when using the MAX1471 in discontinous receive mode. POL_CAL_EN resets when calibration completes properly. (See the Calibration section.) FSK_CAL_EN FSK calibration enable 0 0 FSK_CAL_EN starts the FSK receiver calibration. FSK_CAL_EN resets when calibration completes properly. (See the Calibration section.) Table 9. Status Register (Read Only) (Address: 0x9) BIT ID BIT NAME BIT LOCATION (0 = LSB) LOCKDET Lock detect 7 0 = Internal PLL is not locked so the MAX1471 will not receive data. 1 = Internal PLL is locked. AGCST AGC state 6 0 = LNA in low-gain state. 1 = LNA in high-gain state. CLKALIVE Clock/crystal alive 5 0 = No valid clock signal seen at the crystal inputs. 1 = Valid clock at crystal inputs. X None 4, 3, 2 POL_CAL_DONE Polling timer calibration done 1 0 = Polling timer calibraton in progress or not completed. 1 = Polling timer calibration is complete. FSK_CAL_DONE FSK calibration done 0 0 = FSK calibration in progress or not completed. 1 = FSK calibration is compete. FUNCTION Don’t care. ______________________________________________________________________________________ 23 MAX1471 Table 8. Control Register (Address: 0x2) MAX1471 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver CS DIO tOFF tOFF tCPU tCPU tLOW tRF tRF ADATA OR FDATA Figure 12. DRX Mode Sequence of the MAX1471 Table 10. Off-Timer (tOFF) Configuration PRESCALE1 PRESCALE0 tOFF TIME BASE (1 LSB) MIN tOFF REG 0x4 = 0x00 REG 0x5 = 0x01 0 0 120µs 120µs 7.86s 0 1 480µs 480µs 31.46s 1 0 1920µs 1.92ms 2 min 6s 1 1 7680µs 7.68ms 8 min 23s Table 11. CPU Recovery Timer (tCPU) Configuration 24 TIME BASE (1 LSB) MIN tCPU REG 0x6 = 0x01 MAX tCPU REG 0x6 = 0xFF 120µs 120µs 30.72ms MAX tOFF REG 0x4 = 0xFF REG 0x5 = 0xFF Table 12. RF Settle Timer (tRF) Configuration TIME BASE (1 LSB) MIN tRF REG 0x7 = 0x00 REG 0x8 = 0x01 MAX tRF REG 0x7 = 0xFF REG 0x8 = 0xFF 120µs 120µs 7.86s ______________________________________________________________________________________ 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver PROCESS: CMOS Package Information For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO. 32 TQFN-EP T3255+3 21-0140 90-0001 ______________________________________________________________________________________ 25 MAX1471 Chip Information MAX1471 315MHz/434MHz Low-Power, 3V/5V ASK/FSK Superheterodyne Receiver Revision History REVISION NUMBER REVISION DATE 2 11/10 Updated Ordering Information, Absolute Maximum Ratings, AC Electrical Characteristics, and Package Information 3 12/10 Updated Ordering Information and AC Electrical Characteristics DESCRIPTION PAGES CHANGED 1, 2, 4, 25 1, 3 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. 26 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2010 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.