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19-0455; Rev 1; 9/98
KIT ATION EVALU LE B AVAILA
3V, Ultra-Low-Power Quadrature Modulator/Demodulator
General Description ____________________________Features
o Combines Quadrature Modulator and Demodulator o Integrated Quadrature Phase Shifters o On-Chip Oscillator (Requires External Tuning Circuit) o On-Chip Divide-by-8 Prescaler o Modulator Input Bandwidth Up to 15MHz o Demodulator Output Bandwidth Up to 9MHz o 51dB Demodulator Voltage Conversion Gain o CMOS-Compatible Enable o 5.9mA Operating Supply Current 1A Shutdown Supply Current
MAX2450
The MAX2450 combines a quadrature modulator and quadrature demodulator with a supporting oscillator and divide-by-8 prescaler on a monolithic IC. It operates from a single +3V supply and draws only 5.9mA. 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 thinfilm resistor for matching to an external IF filter. The baseband outputs are fully differential and have 1.2Vp-p signal swings. The modulator accepts differential I and Q baseband signals with amplitudes up to 1.35Vp-p and bandwidths to 15MHz, and produces a differential IF signal in the 35MHz to 80MHz range. Pulling the CMOS-compatible ENABLE pin low shuts down the MAX2450 and reduces the supply current to less than 1A. To minimize spurious feedback, the MAX2450's internal oscillator is set at twice the IF via external tuning components. The oscillator and associated phase shifters produce differential signals exhibiting low amplitude and phase imbalance, yielding modulator sideband rejection of 38dB. The MAX2450 comes in a QSOP package.
Ordering Information
PART MAX2450CEP TEMP. RANGE 0C to +70C PIN-PACKAGE 20 QSOP
Applications
Digital Cordless Phones GSM and North American Cellular Phones Wireless LANs Digital Communications Two-Way Pagers
DEMODULATOR IF_IN 20 BIAS 15 400 14 Q_OUT Q_OUT 17 16 I _OUT I_OUT
Functional Diagram
Pin Configuration
TOP VIEW
IF_OUT 1 IF_OUT 2 GND 3 I_IN 4 I_IN 5 Q_IN 6 Q_IN 7 ENABLE 8 20 IF_IN 19 GND 18 VCC 17 I_OUT
LO_VCC TANK TANK LO_GND I_IN I_IN 10 11 12 13 4 5 MODULATOR 6 Q_IN 7 Q_IN 18 VCC LOCAL OSCILLATOR
/2
0 PRESCALER
/4
9
PRE_OUT
MAX2450
16 I_OUT 15 Q_OUT 14 Q_OUT 13 LO_GND 12 TANK 11 TANK
QUADRATURE PHASE GENERATOR / 2 90
MAX2450
1 IF_OUT 2 IF_OUT
PRE_OUT 9 LO_VCC 10
MASTER BIAS BANDGAP 3, 19 GND BIAS 8 ENABLE
QSOP
________________________________________________________________ Maxim Integrated Products
1
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3V, Ultra-Low-Power Quadrature Modulator/Demodulator MAX2450
ABSOLUTE MAXIMUM RATINGS
VCC, LO_VCC to GND............................................-0.3V to +4.5V ENABLE, TANK, TANK, I_IN, I_IN, Q_IN, Q_IN to GND ..................................................-0.3V to (VCC + 0.3V) IF_IN to GND .........................................................-0.3V to +1.5V Continuous Power Dissipation (TA = +70C) QSOP (derate 9.1mW/C above +70C) ......................727mW 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
PARAMETER Supply Voltage Range Supply Current Shutdown Supply Current Enable/Disable Time ENABLE Bias Current ENABLE High Voltage ENABLE Low Voltage I_IN, I_IN, Q_IN, Q_IN Self-Bias DC Voltage Level Modulator Differential Input Impedance IF_OUT, IF_OUT DC Bias Voltage Demodulator IF Input Impedance Demodulator I and Q Baseband DC Offset I_OUT, I_OUT, Q_OUT, Q_OUT DC Bias Voltage Level VI_OUT/I_OUT, VQ_OUT/Q_OUT SYMBOL VCC, LO_VCC ICC(ON) ICC(OFF) tON/OFF IEN VENH VENL VI_IN/I_IN, VQ_IN/Q_IN ZI_IN/I_IN, ZQ_IN/Q_IN VIF_OUT/IF_OUT ZIF_IN
(VCC = LO_VCC = TANK = 2.7V to 3.3V, ENABLE = VCC - 0.4, GND = LO_GND = 0V, I_IN = I_IN = Q_IN = Q_IN = IF_IN = TANK = OPEN, TA = 0C to +70C, unless otherwise noted.)
CONDITIONS
MIN 2.7
TYP 5.9 2 10 1
ENABLE = 0.4V ENABLE = VCC VCC - 0.4
MAX 3.3 8.2 20 3 0.4
UNITS V mA A s A V V V k V mV V
1.25 35
1.5 44 VCC - 1.5 400 11 1.2
1.75
320
480 50
AC ELECTRICAL CHARACTERISTICS
(MAX2450 EV kit, VCC = LO_VCC = ENABLE = 3.0V, fLO = 140MHz, fI_IN/I_IN = fQ_IN/Q_IN = 600kHz, VI_IN/I_IN = VQ_IN/Q_IN = 1.2Vp-p, fIF_IN = 70.1MHz, VIF_IN = 2.82mVp-p, TA = +25C, unless otherwise noted.) PARAMETER DEMODULATOR I and Q Amplitude Balance I and Q Phase Accuracy Voltage Conversion Gain Allowable I and Q Voltage Swing Noise Figure I and Q IM3 Level I and Q IM5 Level I and Q Signal 3dB Bandwidth Oscillator Frequency Range LO Phase Noise PRE_OUT Output Voltage PRE_OUT Slew Rate 2 VPRE_OUT SRPRE_OUT NF IM3I/Q IM5I/Q BWDEMOD fLO (Notes 1, 3) 10kHz offset RL = 10k, CL < 6pF RL = 10k, CL < 6pF, rising edge 70 -80 0.35 60 (Note 2) (Note 2) (Note 1) 18 -44 -60 9 160 < 0.45 < 1.3 51 1.35 dB degrees dB Vp-p dB dBc dBc MHz MHz dBc/Hz Vp-p V/s SYMBOL CONDITIONS MIN TYP MAX UNITS
_______________________________________________________________________________________
3V, Ultra-Low-Power Quadrature Modulator/Demodulator
AC ELECTRICAL CHARACTERISTICS (continued)
(MAX2450 EV kit, VCC = LO_VCC = ENABLE = 3.0V, fLO = 140MHz, fI_IN/I_IN = fQ_IN/Q_IN = 600kHz, VI_IN/I_IN = VQ_IN/Q_IN = 1.2Vp-p, fIF_IN = 70.1MHz, VIF_IN = 2.82mVp-p, TA = +25C, unless otherwise noted.) PARAMETER MODULATOR Allowable Differential Input Voltage Input Common-Mode Voltage Range I and Q Signal 3dB Bandwidth IF Differential Output Voltage VI_IN/I_IN, VQ_IN/Q_IN BWMOD VIF_OUT/IF_OUT IM3IF IM5IF VI_IN/I_IN, = VQ_IN/Q_IN = 1.2Vp-p, RL = 200k differential, CL < 5pF differential VI_IN/I_IN = 1.35Vp-p composite (Note 4) VI_IN/I_IN = 1.35Vp-p composite (Note 4) (Note 1) 1.25 15 65 1.35 1.75 Vp-p V MHz mVp-p dBc dBc dBc dBc SYMBOL CONDITIONS MIN TYP MAX UNITS
MAX2450
IF Output IM3 Level IF Output IM5 Level Sideband Rejection Carrier Suppression at Modulator Output Note 1: Note 2: Note 3:
-60 -60 38 -36
Guaranteed by design, not tested. fIF_IN = 2 tones at 70.10MHz and 70.11MHz. VIF_IN = 1.41mVp-p per tone. The frequency range can be extended in either direction, but has not been characterized. At higher frequencies, the modulator IF output amplitude may decrease and distortions may increase. Note 4: Q_IN/Q_IN ports are terminated. fI_IN/I_IN = 2 tones at 550kHz and 600kHz.
__________________________________________Typical Operating Characteristics
(MAX2450 EV kit, VCC = LO_VCC = ENABLE = 3.0V, fLO = 140MHz, fI_IN/I_IN = fQ_IN/Q_IN = 600kHz, VI_IN/I_IN = VQ_IN/Q_IN = 1.2Vp-p, fIF_IN = 70.1MHz, VIF_IN = 2.82mVp-p, TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
MAX2450-01
SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE
MAX2450-02
MODULATOR IF OUTPUT vs. BASEBAND INPUT
MAX2450-03
7.0 6.8 SUPPLY CURRENT (mA) 6.6 6.4 6.2 6.0 5.8 5.6 5.4 5.2 5.0 0 10 20 30 40 50 60 70 VCC = 2.7V VCC = 3.0V VCC = 3.3V
12 10 SUPPLY CURRENT (A) 8 6 4 2 0 VCC = 2.7V VCC = 3.0V VCC = 3.3V
-30 -34 OUTPUT (dBVRMS) -38 -42 -46 -50 -54
dBVRMS 20
Vp-p = 2 2 x 10
(V)
80
0
10
20
TEMPERATURE (C)
50 60 TEMPERATURE (C)
30
40
70
80
-26
-22
-18
-14
-10
-6
BASEBAND INPUT (dBVRMS)
_______________________________________________________________________________________
3
3V, Ultra-Low-Power Quadrature Modulator/Demodulator MAX2450
____________________________Typical Operating Characteristics (continued)
(MAX2450 EV kit, VCC = LO_VCC = ENABLE = 3.0V, fLO = 140MHz, fI_IN/I_IN = fQ_IN/Q_IN = 600kHz, VI_IN/I_IN = VQ_IN/Q_IN = 1.2Vp-p, fIF_IN = 70.1MHz, VIF_IN = 2.82mVp-p, TA = +25C, unless otherwise noted.)
MODULATOR IF OUTPUT vs. SUPPLY VOLTAGE
MAX2450-04
MODULATOR IF OUTPUT vs.TEMPERATURE
MAX2450-05
MODULATOR SIDEBAND REJECTION vs. IF FREQUENCY
VI_IN/I_IN = 1.2Vp-p VQ_IN/Q_IN = 1.2Vp-p
MAX2450-06
70
70 VCC = 3V 68 IF OUTPUT (mVp-p)
-30 SIDEBAND REJECTION (dBc) -32 -34 -36 -38 -40 -42
68 IF OUTPUT (mVp-p) TA = +70C 66 TA = +25C 64 TA = 0C 62
66
64
62
60 2.7 2.8 2.9 3.0 VCC (V) 3.1 3.2 3.3
60 0 20 40 60 80 TEMPERATURE (C)
-44 35 40 45 50 55 60 65 70 75 80 IF FREQUENCY (MHz)
MODULATOR SIDEBAND REJECTION vs. TEMPERATURE
MAX2450-07
CARRIER SUPPRESSION vs. IF FREQUENCY
MAX2450-08
PRE_OUT WAVEFORM
MAX2450-09
-36 SIDEBAND REJECTION (dBc) VI_IN/I_IN = 1.2Vp-p VQ_IN/Q_IN = 1.2Vp-p -38
-30 CARRIER SUPPRESSION (dBc) -32 -34 -36 -38 -40 -42 VI_IN/I_IN = 1.2Vp-p VQ_IN/Q_IN = 1.2Vp-p
-40
100mV/ div
-42
RL = 10k CL < 6pF 40 45 50 55 60 65 70
-44 0 20 40 60 80 TEMPERATURE (C)
-44 35 75 80 20ns/div IF FREQUENCY (MHz)
MODULATOR OUTPUT SPECTRUM
VI_IN/I_IN = 1.2Vp-p VQ_IN/Q_IN = 1.2Vp-p
MAX2450-10
0 -10 -20 (dBc) -30 -40 -50 -60 69.0 69.4 70.0 (MHz) 70.6
71.0
4
_______________________________________________________________________________________
3V, Ultra-Low-Power Quadrature Modulator/Demodulator
____________________________Typical Operating Characteristics (continued)
(MAX2450 EV kit, VCC = LO_VCC = ENABLE = 3.0V, fLO = 140MHz, fI_IN/I_IN = fQ_IN/Q_IN = 600kHz, VI_IN/I_IN = VQ_IN/Q_IN = 1.2Vp-p, fIF_IN = 70.1MHz, VIF_IN = 2.82mVp-p, TA = +25C, unless otherwise noted.)
DEMODULATOR VOLTAGE CONVERSION GAIN vs. TEMPERATURE AND SUPPLY
MAX2450-11
MAX2450
DEMODULATOR VOLTAGE CONVERSION GAIN vs. IF FREQUENCY
MAX2450-12
DEMODULATOR VOLTAGE CONVERSION GAIN vs. BASEBAND FREQUENCY
50 49 GAIN (dBV) 48 47 46 45
MAX2450-13
51.5 TA = 0C 51.0 50.5 GAIN (dBV) 50.0 49.5 TA = +50C 49.0 48.5 TA = +70C 48.0 2.6 2.7 2.8 2.9 3.0 3.1 VCC (V) 3.2 3.3 TA = +25C
51.4
51
51.2 GAIN (dBV)
51.0
50.8
44 43
50.6 3.4 35 40 45 50 55 60 65 70 75 80 IF FREQUENCY (MHz)
42 10k 100k 1M 10M 100M BASEBAND FREQUENCY (Hz)
DEMODULATOR I/Q PHASE AND AMPLITUDE MISMATCH vs. TEMPERATURE
MAX2450-15
DEMODULATOR INTERMOD POWER vs. TEMPERATURE
MAX2450-16
1.6 MATCHING (DEGREES OR dBV) 1.4 1.2 1.0 0.8 0.6 0.4 0 10 20 30 40 50 60 PHASE MATCH
-40 IM3 INTERMODULATION (dBc) -45
-50 fOSC = 140MHz fIF1 = 70.1MHz fIF2 = 70.11MHz VIF_IN = 2.82mVp-p IM5 -65
-55
-60 AMPLITUDE MATCH 70 0 10 20 30
40
50
60
70
TEMPERATURE (C)
TEMPERATURE (C)
_______________________________________________________________________________________
5
3V, Ultra-Low-Power Quadrature Modulator/Demodulator MAX2450
______________________________________________________________Pin Description
PIN 1 2 3, 19 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 20 NAME IF_OUT IF_OUT GND I_IN I_IN Q_IN Q_IN ENABLE PRE_OUT LO_VCC TANK TANK LO_GND Q_OUT Q_OUT I_OUT I_OUT VCC IF_IN Modulator IF Output Modulator IF Inverting Output Ground Baseband Inphase Input Baseband Inphase Inverting Input Baseband Quadrature Input Baseband Quadrature Inverting Input Enable Control, active high Local-Oscillator, Divide-by-8, Prescaled Output Local-Oscillator Supply. Bypass separately from VCC. Local-Oscillator Resonant Tank Input (Figure 4) Local-Oscillator Resonant Tank Inverting Input (Figure 4) Local-Oscillator Ground Demodulator Quadrature Inverting Output Demodulator Quadrature Output Demodulator Inphase Inverting Output Demodulator Inphase Output Modulator and Demodulator Supply Demodulator IF Input FUNCTION
2
A/D CONVERSION
2
A/D CONVERSION DSP
R T UP/DOWNCONVERTER
0 90
/8
2
2
D/A CONVERSION
MAX2450
D/A CONVERSION
Figure 1. Typical Application Block Diagram
6 _______________________________________________________________________________________
3V, Ultra-Low-Power Quadrature Modulator/Demodulator MAX2450
LO_VCC
MAX2450-fig03
75 RL 5k Q3 TANK TANK RL 5k OUTPUT LEVEL (mVp-p) Q4 70 65 60 55 50 45 40 35 200 1k 10k
Q1
Q2
TO QUADRATURE GENERATOR AND PRESCALER
100k
LOAD RESISTANCE ()
Figure 2. Local-Oscillator Equivalent Circuit
Figure 3. Modulator Output Level vs. Load Resistance
_______________Detailed Description
The following sections describe each of the functional blocks shown in the Functional Diagram. They also refer to the Typical Application Block Diagram (Figure 1).
Demodulator
The demodulator contains a single-ended-to-differential converter, two Gilbert-cell multipliers, and two fixed gain stages. The IF signal should be AC coupled into IF_IN. Internally, IF_IN is terminated with a 400 resistor to GND and provides a gain of 14dB. This amplified IF signal is fed into the I and Q 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 I and Q amplifier chains are DC coupled.
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 single-ended drive, connect an AC bypass capacitor (1000pF) from TANK to GND, and AC couple TANK to the source.
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.
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.
Local Oscillator
The local-oscillator section is formed by an emitter-coupled differential pair. Figure 2 shows the equivalent local-oscillator 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, so that the quadrature phase generator can use two latches to generate precise quadrature signals. The oscillator may be overdriven by an external source. The source should be AC coupled into TANK/TANK,
Modulator
The modulator accepts I and Q differential baseband signals up to 1.35Vp-p with frequencies up to 15MHz, and upconverts them to the IF frequency. Since these inputs are biased internally at around 1.5V, I and Q signals should be capacitively coupled into these highimpedance ports (the differential input impedance is approximately 44k). The self-bias design yields very low on-chip offset, resulting in excellent carrier sup7
_______________________________________________________________________________________
3V, Ultra-Low-Power Quadrature Modulator/Demodulator
pression. Alternatively, a differential DAC may be connected without AC coupling, as long as a commonmode voltage range of 1.25V to 1.75V is maintained. For single-ended drive, connect I_IN and Q_IN via ACcoupling capacitors (0.1F) to GND. The IF output is designed to drive a high impedance (> 20k), such as an IF buffer or an upconverter mixer. IF_OUT/IF_OUT must be AC coupled to the load. Impedances as low as 200 can be driven with a decrease in output amplitude (Figure 3). To drive a single-ended load, AC couple and terminate IF_OUT with a resistive load equal to the load at IF_OUT.
MAX2450
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.
Master Bias
During normal operation, ENABLE should remain above VCC - 0.4V. Pulling the ENABLE input low shuts off the master bias and reduces the circuit current to less than 2A. The master bias section includes a bandgap reference generator and a PTAT (Proportional To Absolute Temperature) current generator.
TANK C1 = 33pF 47k
1/2 KV1410 L = 100nH 10k
0.1F VCTRL
__________Applications Information
Figure 4 shows the implementation of a resonant tank circuit. The inductor, two capacitors, and a dual varactor form the oscillator's resonant circuit. In Figure 4, 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 application requirements. Use the following formula to determine the oscillation frequency: fo = where CEQ = and LEQ = L + LSTRAY where CSTRAY = parasitic capacitance and LSTRAY = parasitic inductance. 1 + CSTRAY 1 1 2 + + C1 C2 C VAR 1 2 LEQCEQ
1/2 KV1410 47k TANK C2 = 33pF
Figure 4. Typical Resonant Tank Circuit
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.
8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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