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19-0493; Rev 0; 12/95
K ATION EVALU BLE AVAILA
IT
3V, Ultra-Low-Power Quadrature Demodulator
____________________________Features
o Integrated Quadrature Phase Shifters o On-Chip Oscillator (Requires External Tuning Circuit) o 51dB Voltage Conversion Gain o On-Chip Divide-by-8 Prescaler o Baseband Output Bandwidth Up to 9MHz o CMOS-Compatible Enable o 5.5mA Operating Supply Current 2A Shutdown Supply Current
_______________General Description
The monolithic MAX2451 is a quadrature demodulator with a supporting oscillator and divide-by-8 prescaler. It operates from a single +3V supply and draws only 5.5mA. The demodulator accepts an amplified and filtered IF signal in the 35MHz to 80MHz range, and demodulates it into I and Q baseband signals with 51dB of voltage conversion gain. The IF input is terminated with a 400 thin-film resistor for matching to an external IF filter. The baseband outputs are fully differential and have 1.2Vp-p signal swings. Pulling the CMOS-compatible ENABLE pin low shuts down the MAX2451 and reduces the supply current to less than 2A, typical. To minimize spurious feedback, the MAX2451's internal oscillator is set at twice the IF frequency via external tuning components. The MAX2451 comes in a 16-pin narrow SO package.
MAX2451
________________________Applications
Digital Cordless Phones GSM and North American Cellular Phones Wireless LANs Digital Communications Pagers
______________Ordering Information
PART MAX2451CSE TEMP. RANGE 0C to +70C PIN-PACKAGE 16 Narrow SO
________________Functional Diagram
14 I I
__________________Pin Configuration
IF 1
13 DEMODULATOR BIAS 12 400 11
TOP VIEW
Q Q
IF 1 GND 2 GND 3 N.C. 4 ENABLE 5 PRE_OUT 6 LO_VCC 7 TANK 8
16 GND 15 VCC 14 I
LO_VCC TANK TANK LO_GND VCC 7 8 9 10 15 MASTER BIAS BANDGAP BIAS LOCAL OSCILLATOR
/2
0 PRESCALER
/4
6
PRE_OUT
MAX2451
13 I 12 Q 11 Q 10 LO_GND 9 TANK
QUADRATURE PHASE GENERATOR / 2 90
MAX2451
SO
2, 3, 16 GND
5 ENABLE
________________________________________________________________ Maxim Integrated Products
1
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3V, Ultra-Low-Power Quadrature Demodulator MAX2451
ABSOLUTE MAXIMUM RATINGS
VCC, LO_VCC to GND............................................-0.3V to +4.5V ENABLE, TANK, TANK, I, I, Q, Q to GND.............................................-0.3V to (VCC + 0.3V) IF to GND...............................................................-0.3V to +1.5V Continuous Power Dissipation (TA = +70C) Narrow SO (derate 8.70mW/C above +70C) .............696mW Operating Temperature Range...............................0C to +70C Storage Temperature Range .............................-65C to +165C Lead Temperature (soldering, 10sec) .............................+300C
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 = LO_VCC = TANK = +2.7V to +3.3V, ENABLE = VCC - 0.4V, GND = LO_GND = 0V, I = I = Q = Q = IF = TANK = OPEN, TA = 0C to +70C, unless otherwise noted.) PARAMETER Supply Voltage Range Supply Current Shutdown Supply Current Enable/Disable Time ENABLE Bias Current ENABLE High Voltage ENABLE Low Voltage IF Input Impedance I, I, Q, Q Voltage Level Baseband I and Q DC Offset SYMBOL VCC, LO_VCC ICC(ON) ICC(OFF) tON/OFF IEN VENH VENL ZIN VI/I, VQ/Q 320 400 1.2 11 50 VCC - 0.4 0.4 480 Enable = 0.4V CONDITIONS MIN 2.7 5.5 2 10 1 3 TYP MAX 3.3 7.4 20 UNITS V mA A s A V V V mV
AC ELECTRICAL CHARACTERISTICS
VCC = LO_VCC = ENABLE = 3.0V, fLO = 140MHz, fIF = 70.1MHz, VIF = 2.82mVp-p, TA = +25C, unless otherwise noted.) PARAMETER Baseband I and Q Amplitude Balance Baseband I and Q Phase Accuracy Voltage Conversion Gain Noise Figure Allowable I and Q Voltage Swing I and Q IM3 Level I and Q IM5 Level I and Q Signal 3dB Bandwidth Oscillator Frequency Range PRE_OUT Output Voltage PRE_OUT Slew Rate Oscillator Phase Noise Note 1: Note 2: Note 3: 2 IM3I/Q IM5I/Q BW3dB fLO VPRE_OUT SRPRE_OUT (Notes 1, 3) RL = 10k, CL < 6pF RL = 10k, CL < 6pF, rising edge Offset = 10kHz 70 0.35 60 -80 NF (Note 1) (Note 2) (Note 2) -44 -60 9 160 SYMBOL CONDITIONS MIN TYP < 0.45 < 1.3 51 18 1.35 MAX UNITS dB degrees dB dB Vp-p dBc dBc MHz MHz Vp-p V/s dBc/Hz
Guaranteed by design, not tested. fIF = 2 tones at 70.10MHz and 70.11MHz, VIF = 1.41mVp-p per tone. Oscillator frequencies up to 1GHz (500MHz IF) by externally overdriving (see Applications Information).
_______________________________________________________________________________________
3V, Ultra-Low-Power Quadrature Demodulator
__________________________________________Typical Operating Characteristics
(VCC = LO_VCC = ENABLE = 3.0V, fLO = 140MHz, fIF = 70.1MHz, VIF = 2.82mVp-p, TA = +25C, unless otherwise noted.)
MAX2451
SUPPLY CURRENT vs. TEMPERATURE
MAX2451-01
SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE
VCC = 3.0V 6 SHUTDOWN ICC (A) 5 4 3 2 1 0
MAX2451-02
VOLTAGE CONVERSION GAIN vs. TEMPERATURE AND SUPPLY VOLTAGE
TA = 0C 51.0 50.5 GAIN (dBV) 50.0 49.5 TA = +50C 49.0 48.5 TA = +70C 48.0 TA = +25C
MAX2451-03
6.4 VCC = 3.0V 6.2 6.0 ICC (mA) 5.8 5.6 5.4 5.2 0 10 20 30 40 50 60
7
51.5
70
0
10
20
30
40
50
60
70
2.6
2.7
2.8
2.9 3.0 3.1 VCC (V)
3.2
3.3
3.4
TEMPERATURE (C)
TEMPERATURE (C)
VOLTAGE CONVERSION GAIN vs. IF FREQUENCY
MAX2451-04
PHASE AND AMPLITUDE MATCHING vs. TEMPERATURE
MAX2451-05
INTERMODULATION POWER vs. TEMPERATURE
MAX2451-06
52 51 50 49 GAIN (dBV) 48 47 46 45 44 43 42 0 100 200 300 400 fBASEBAND = 100kHz VLO_INJECT = 40mVRMS = 113mVp-p into 5O VIF_IN = 2.82mVP-P
1.6 MATCHING (DEGREES OR dBV) 1.4 1.2 1.0 0.8 0.6 0.4 PHASE MATCH
-40 IM3 INTERMODULATION (dBc) -45
-50 fLO = 140MHz fIF1 = 70.10MHz fIF2 = 70.11MHz VIF_IN = 1.41mVp-p per tone IM5 -65
-55
-60
AMPLITUDE MATCH 0 10 20 30 40 50 60 70
0 10 20 30
500
40
50
60
70
IF FREQUENCY (MHz)
TEMPERATURE (C)
TEMPERATURE (C)
PRE_OUT WAVEFORM
MAX2451-07
100mV/div
RL = 10k CL < 6pF 20ns/div
_______________________________________________________________________________________
3
3V, Ultra-Low-Power Quadrature Demodulator MAX2451
_____________________Pin Description
PIN 1 2, 3, 16 4 5 6 7 8 9 10 11 12 13 14 15 NAME IF GND N.C. ENABLE PRE_OUT LO_VCC TANK TANK LO_GND Q Q I I VCC IF Input Ground No Connect. No internal connection to this pin. Enable Control, active high Local-Oscillator Divide-by-8 Prescaled Output Local-Oscillator Supply. Bypass separately from VCC. Local-Oscillator Resonant Tank Input Local-Oscillator Resonant Tank Inverting Input Local-Oscillator Ground Baseband Quadrature Inverting Output Baseband Quadrature Output Baseband Inphase Inverting Output Baseband Inphase Output Demodulator Supply
0 90 2 2 DOWNCONVERTER
FUNCTION
A/D
POST PROCESSING
A/D
MAX2451
/8
Figure 1. Typical Application Block Diagram
_______________Detailed Description
The following sections describe each of the functional blocks shown in the Functional Diagram. Also refer to the Typical Application Block Diagram (Figure 1).
Local Oscillator
The local-oscillator section is formed by an emitter-coupled differential pair. Figure 2 shows the local-oscillator equivalent circuit schematic. An external LC resonant tank determines the oscillation frequency, and the Q of this resonant tank affects the oscillator phase noise. The oscillation frequency is twice the IF frequency, for easy generation of quadrature signals. The oscillator may be overdriven by an external source. The source should be AC coupled into TANK/TANK, and should provide 200mVp-p levels. A choke (typically 2.2H) is required between TANK and TANK. Differential input impedance at TANK/TANK is 10k. For singleended drive, connect an AC bypass capacitor (1000pF) from TANK to GND, and AC couple TANK to the source. The oscillator can be overdriven at frequencies up to 1GHz (500MHz IF), but conversion gain and prescaler output levels will be somewhat reduced.
Demodulator
The demodulator contains a single-ended-to-differential converter, two Gilbert-cell multipliers, and two fixed gain stages. Internally, IF is terminated with a 400 resistor to GND. The IF input signal is AC coupled into the input amplifier, which has 14dB of gain. This amplified IF signal is fed into the I and Q channel mixers for demodulation. The multipliers mix the IF signal with the quadrature LO signals, resulting in baseband I and Q signals. The conversion gain of the multipliers is 15dB. These signals are further amplified by 21dB by the baseband amplifiers. The baseband amplifier chains are DC coupled.
4
_______________________________________________________________________________________
3V, Ultra-Low-Power Quadrature Demodulator MAX2451
LO_VCC
RL 5k Q3 TANK TANK
RL 5k Q4
TANK
C1 = 33pF
47k
1/2 KV1410 L = 100nH Q1 Q2 TO QUADRATURE GENERATOR AND PRESCALER TANK C2 = 33pF 1/2 KV1410 47k 10k
0.1F VCTRL
Figure 2. Local-Oscillator Equivalent Circuit
Figure 3. Typical Resonant Tank Circuit
Quadrature Phase Generator
The quadrature phase generator uses two latches to divide the local-oscillator frequency by two, and generates two precise quadrature signals. Internal limiting amplifiers shape the signals to approximate square waves to drive the Gilbert-cell mixers. The inphase signal (at half the local oscillator frequency) is further divided by four for the prescaler output.
cation requirements. The oscillation frequency can be determined using the following formula: 1 2 LEQCEQ
fo = where CEQ = and
Prescaler
The prescaler output, PRE_OUT, is buffered and swings typically 0.35Vp-p with a 10k and 6pF load. It can be AC coupled to the input of a frequency synthesizer.
1 + C STRAY 1 1 2 + + C1 C2 C VAR LEQ = L + LSTRAY
Master Bias
During normal operation, ENABLE should be above VCC - 0.4V. Pulling the ENABLE input low shuts off the master bias and reduces the circuit current to typically 2A. The master bias section includes a bandgap reference generator and a PTAT (Proportional To Absolute Temperature) current generator.
__________Applications Information
Figure 3 shows the implementation of a resonant tank circuit. The inductor, two capacitors, and a dual varactor form the oscillator's resonant circuit. In Figure 3, the oscillator frequency ranges from 130MHz to 160MHz. To ensure reliable start-up, the inductor is directly connected across the local oscillator's tank ports. The two 33pF capacitors affect the Q of the resonant circuit. Other values may be chosen to meet individual appli-
where CSTRAY = parasitic capacitance and LSTRAY = parasitic inductance. To alter the oscillation frequency range, change the inductance, the capacitance, or both. For best phasenoise performance, keep the Q of the resonant tank as high as possible: Q = REQ C EQ
LEQ
where REQ 10k (Figure 2). The oscillation frequency can be changed by altering the control voltage, VCTRL.
5
_______________________________________________________________________________________
3V, Ultra-Low-Power Quadrature Demodulator MAX2451
________________________________________________________Package Information
DIM INCHES MAX MIN 0.069 0.053 0.010 0.004 0.019 0.014 0.010 0.007 0.157 0.150 0.050 0.244 0.228 0.050 0.016 MILLIMETERS MIN MAX 1.35 1.75 0.10 0.25 0.35 0.49 0.19 0.25 3.80 4.00 1.27 5.80 6.20 0.40 1.27
D A e B
0.101mm 0.004in.
0-8
A1
C
L
A A1 B C E e H L
E
H
Narrow SO SMALL-OUTLINE PACKAGE (0.150 in.)
DIM PINS D D D 8 14 16
INCHES MILLIMETERS MIN MAX MIN MAX 0.189 0.197 4.80 5.00 0.337 0.344 8.55 8.75 0.386 0.394 9.80 10.00
21-0041A
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.
6 ___________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 (c) 1995 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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