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Unformatted text preview: +85°C 28 TSSOP Typical Application Circuit appears at end of data sheet. Pin Configuration appears at end of data sheet. Medical Systems Functional Diagram LNAOUT MIXIN1 6 LNAIN 3 MIXOUT 8 9 IFIN1 IFIN2 12 MIXIN2 17 18 IF LIMITING AMPS LNA 0° Q MAX1470 LNASRC 4 90° RSSI I DVDD AVDD DGND AGND DIVIDE BY 64 VCO PHASE DETECTOR 14 LOOP FILTER CRYSTAL DRIVER SHUTDOWN DATA FILTER 2,7 RDF2 100kΩ RDF1 100kΩ 13 5,10 1 28 XTAL1 XTAL2 27 PWRDN DATA SLICER 25 DATAOUT PEAK DETECTOR 20 19 DSN DSP 26 PDOUT 21 22 OPP DF ________________________________________________________________ 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 1 315MHz Low-Power, +3V Superheterodyne Receiver MAX1470 Typical Application Circuit +3.3V Y1 4.7547MHz C12 0.01µF ANTENNA (RFIN) XTAL1 XTAL2 28 2 AVDD PWRDN 27 3 LNAIN PDOUT 26 4 LNASRC 5 AGND I.C. 24 6 LNAOUT I.C. 23 7 AVDD 8 C7 100pF 1 MIXIN1 SHUTDOWN L2 100nH L3 15nH +3.3V L1 27nH DATAOUT 25 DATAOUT C2 0.01µF C9 2.2pF C11 100pF MAX1470 DF 22 OPP 21 C5 470pF 9 C10 220pF C8 100pF MIXIN2 DSN 20 10 AGND DSP 19 11 I.C. IFIN2 18 12 MIXOUT IFIN1 17 13 DGND 14 DVDD C1 0.01µF I.C. 16 I.C. 15 U1 10.7MHz C3 1500pF C6 220pF R1 5kΩ C4 0.47µF CTOTAL = C9 + CPARASITICS -118 -116 -114 60 Mixer SYSTEM GAINCrystal Oscillator vs. IF FREQUENCY -40 -20 0 20 Phase-Lock Loop 40 60 80 T he PLL block contains a phase detector, charge TEMPERATURE (°C) pump/integrated loop filter, VCO, asynchronous 64x clock divider, and crystal oscillator. This PLL does not require any external SUPPLY CURRENT components. The quadrature VCO is centered at the nominal LO frequency of 304.3MHz. vs. LO FREQUENCY For an input RF frequency of 315MHz, a reference frequency of 4.7547MHz is needed for a 10.7MHz IF fre7.2 quency (low-side injection is required). The relationship between the RF, IF, and reference frequencies is given by: IF FREQUENCY (MHz) ƒp = Cm 1 1 6 − × 10 2 Ccase + Cload Ccase + Cspec INPUT IMPEDANCE vs. INDUCTIVE DEGENERATION MAX1470 toc09 AX1470 toc08 45 The XTAL oscillator in the MAX1470 is designed to pre60 sent a capacitanceRFINapproximately 3pF between FROM of TO MIXOUT XTAL1 and XTAL2. If a crystal designed to oscillate f load capacitance is used, the crystal is with a differentLO = 304.3MHz 50 pulled away from its stated operating frequency, introUPPER SIDEBAND ducing an error in the reference frequency. Crystals 40 to operate with higher differential load capacdesigned itance always pull the reference frequency higher. For example, a 4.7547MHz crystal designed to operate 30 with a 10pF load capacitance oscillates at 4.7563MHz with the MAX1470, causing the receiver to be tuned to 53dB IMAGE 315.1MHz rather than 315.0MHz, an error of about 20 REJECTION 100kHz, or 320ppm. In actuality, the oscillator pulls every crystal. The crys10 tal’s natural frequency is really below its specified frequency, but when loaded with the specified load LOWER SIDEBAND capacitance, the crystal is pulled and oscillates at its 0 specified frequency. This pulling is already accounted for in the specification of the load capacitance. Additional pulling can be calculated if the electrical -10 parameters0of the crystal are known. The frequency 40 10 20 30 pulling is given by: SYSTEM GAIN (dB) IMAGE REJECTION (dB) A unique feature of the MAX1470 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 55 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 315MHz RF input to the 10.7MHz IF with low-side injection (i.e., fLO = fRF - fIF). The image rejection circuit then combines these signals to achieve ~50dB of image rejection over the 50 full temperature range. Low-side injection is required due to the on-chip image-rejection architecture. 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 13dB. Applications Information MAX1470 toc06 -120 LPARASITICS and CPARASITICS include inductance and AVERAGE board traces, package capacitance of the PC RF INPUT POWER (dBm) 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 IMAGE REJECTION should be done to optifrequency. Lab experimentationvs. TEMPERATURE mize the center frequency of the tank. MAX1470 toc05 0.1 overall gain of approximately 65dB, with a bandpass-filter-type response centered near the 10.7MHz IF frequency with a 3dB bandwidth of approximately 1.0 11.5MHz. The RSSI circuit demodulates the IF to base-140 -120 -100...
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