19-0493; Rev 0; 12/95
KIT
ATION
EVALU
E
BL
AVAILA
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
2µA 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 fil-
tered 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 termi-
nated with a 400Ω thin-film resistor for matching to an
external IF filter. The baseband outputs are fully differ-
ential 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 2µA, 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
0°C to +70°C
PIN-PACKAGE
16 Narrow SO
________________Functional Diagram
14
I
I
__________________Pin Configuration
IF
1
13
DEMODULATOR
BIAS
12
400Ω
11
TOP VIEW
Q
Q
IF 1
GND 2
GND 3
N.C. 4
ENABLE 5
PRE_OUT 6
LO_V
CC
7
TANK 8
16 GND
15 V
CC
14 I
LO_V
CC
TANK
TANK
LO_GND
V
CC
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
Call toll free 1-800-998-8800, or visit our WWW site at http://www.maxim-ic.com
for free samples or the latest literature.
3V, Ultra-Low-Power
Quadrature Demodulator
MAX2451
ABSOLUTE MAXIMUM RATINGS
V
CC
, LO_V
CC
to GND............................................-0.3V to +4.5V
ENABLE, TANK, TANK, I, I,
Q, Q to GND.............................................-0.3V to (V
CC
+ 0.3V)
IF to GND...............................................................-0.3V to +1.5V
Continuous Power Dissipation (T
A
= +70°C)
Narrow SO (derate 8.70mW/°C above +70°C) .............696mW
Operating Temperature Range...............................0°C to +70°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
(V
CC
= LO_V
CC
= TANK = +2.7V to +3.3V, ENABLE = V
CC
- 0.4V, GND = LO_GND = 0V, I = I = Q = Q = IF = TANK = OPEN,
T
A
= 0°C to +70°C, 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
V
CC
,
LO_V
CC
I
CC(ON)
I
CC(OFF)
t
ON/OFF
I
EN
V
ENH
V
ENL
Z
IN
V
I/I
,
V
Q/Q
320
400
1.2
±11
±50
V
CC
- 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
µA
µs
µA
V
V
Ω
V
mV
AC ELECTRICAL CHARACTERISTICS
V
CC
= LO_V
CC
= ENABLE = 3.0V, f
LO
= 140MHz, f
IF
= 70.1MHz, V
IF
= 2.82mVp-p, T
A
= +25°C, 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
IM3
I/Q
IM5
I/Q
BW
3dB
f
LO
V
PRE_OUT
SR
PRE_OUT
(Notes 1, 3)
R
L
= 10kΩ, C
L
< 6pF
R
L
= 10kΩ, C
L
< 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/µs
dBc/Hz
Note 1:
Guaranteed by design, not tested.
Note 2:
f
IF
= 2 tones at 70.10MHz and 70.11MHz, V
IF
= 1.41mVp-p per tone.
Note 3:
Oscillator frequencies up to 1GHz (500MHz IF) by externally overdriving (see
Applications Information).
2
_______________________________________________________________________________________
3V, Ultra-Low-Power
Quadrature Demodulator
__________________________________________Typical Operating Characteristics
(V
CC
= LO_V
CC
= ENABLE = 3.0V, f
LO
= 140MHz, f
IF
= 70.1MHz, V
IF
= 2.82mVp-p, T
A
= +25°C, unless otherwise noted.)
MAX2451
SUPPLY CURRENT
vs. TEMPERATURE
MAX2451-01
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
V
CC
= 3.0V
6
SHUTDOWN I
CC
(µA)
5
4
3
2
1
0
MAX2451-02
VOLTAGE CONVERSION GAIN vs.
TEMPERATURE AND SUPPLY VOLTAGE
T
A
= 0°C
51.0
50.5
GAIN (dBV)
50.0
49.5
T
A
= +50°C
49.0
48.5
T
A
= +70°C
48.0
T
A
= +25°C
MAX2451-03
6.4
V
CC
= 3.0V
6.2
6.0
I
CC
(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
V
CC
(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
f
BASEBAND
= 100kHz
V
LO_INJECT
= 40mV
RMS
= 113mVp-p
into 5OΩ
V
IF_IN
= 2.82mV
P-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
f
LO
= 140MHz
f
IF1
= 70.10MHz
f
IF2
= 70.11MHz
V
IF_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
R
L
= 10kΩ
C
L
< 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_V
CC
TANK
TANK
LO_GND
Q
Q
I
I
V
CC
IF Input
Ground
No Connect. No internal connec-
tion to this pin.
Enable Control, active high
Local-Oscillator Divide-by-8
Prescaled Output
Local-Oscillator Supply. Bypass
separately from V
CC
.
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-cou-
pled 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
2.2µH) is required between TANK and TANK. Differential
input impedance at TANK/TANK is 10kΩ. For single-
ended 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 400Ω
resistor to GND. The IF input signal is AC coupled into
the input amplifier, which has 14dB of gain. This ampli-
fied 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_V
CC
R
L
5k
Q3
TANK
TANK
R
L
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
0.1µF
V
CTRL
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 gener-
ates two precise quadrature signals. Internal limiting
amplifiers shape the signals to approximate square
waves to drive the Gilbert-cell mixers. The inphase sig-
nal (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
π
L
EQ
C
EQ
1
1
1
2
+
+
C1 C2 C
VAR
+
C
STRAY
f
o
=
where
C
EQ
=
and
Prescaler
The prescaler output, PRE_OUT, is buffered and swings
typically 0.35Vp-p with a 10kΩ and 6pF load. It can be
AC coupled to the input of a frequency synthesizer.
Master Bias
During normal operation, ENABLE should be above
V
CC
- 0.4V. Pulling the ENABLE input low shuts off the
master bias and reduces the circuit current to typically
2µA. The master bias section includes a bandgap ref-
erence generator and a PTAT (Proportional To Absolute
Temperature) current generator.
L
EQ
=
L
+
L
STRAY
where C
STRAY
= parasitic capacitance and L
STRAY
=
parasitic inductance.
To alter the oscillation frequency range, change the
inductance, the capacitance, or both. For best phase-
noise performance, keep the Q of the resonant tank as
high as possible:
Q
=
R
EQ C EQ
LEQ
__________Applications Information
Figure 3 shows the implementation of a resonant tank
circuit. The inductor, two capacitors, and a dual varac-
tor 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 con-
nected 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 R
EQ
≈
10kΩ (Figure 2).
The oscillation frequency can be changed by altering
the control voltage, V
CTRL
.
5
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