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_______________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 400
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.
________________________Applications
Digital Cordless Phones
GSM and North American Cellular Phones
Wireless LANs
Digital Communications
Pagers
____________________________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
MAX2451
3V, Ultra-Low-Power
Quadrature Demodulator
________________________________________________________________
Maxim Integrated Products
1
ENABLE
GND
400
5
2, 3, 16
6
PRE_OUT
11
Q
12
Q
13
I
14
I
1
IF
7
LO_V
CC
V
CC
8
TANK
9
TANK
15
10
LO_GND
BIAS
PRESCALER
DEMODULATOR
QUADRATURE
PHASE
GENERATOR
LOCAL
OSCILLATOR
÷
2
÷
4
BANDGAP
BIAS
MASTER BIAS
÷
2
0°
90°
MAX2451
________________Functional Diagram
16
15
14
13
12
11
10
9
1
2
3
4
5
6
7
8
GND
V
CC
I
I
Q
Q
LO_GND
TANK
IF
GND
GND
N.C.
ENABLE
PRE_OUT
LO_V
CC
TANK
TOP VIEW
MAX2451
SO
__________________Pin Configuration
19-0493; Rev 0; 12/95
PART
MAX2451CSE
0°C to +70°C
TEMP. RANGE
PIN-PACKAGE
16 Narrow SO
______________Ordering Information
EVALUATION KIT
AVAILABLE
MAX2451
3V, Ultra-Low-Power
Quadrature Demodulator
2
_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
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.)
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.)
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.
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).
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
Enable = 0.4V
CONDITIONS
µA
2
20
I
CC(OFF)
Shutdown Supply Current
mA
5.5
7.4
I
CC(ON)
V
2.7
3.3
V
CC
,
LO_V
CC
Supply Voltage Range
Supply Current
V
1.2
V
I/I
,
V
Q/Q
I, I, Q, Q Voltage Level
320
400
480
Z
IN
IF Input Impedance
µs
10
t
ON/OFF
Enable/Disable Time
µA
1
3
I
EN
ENABLE Bias Current
V
V
CC
- 0.4
V
ENH
ENABLE High Voltage
V
0.4
V
ENL
ENABLE Low Voltage
UNITS
MIN
TYP
MAX
SYMBOL
PARAMETER
(Notes 1, 3)
(Note 1)
(Note 2)
(Note 2)
CONDITIONS
degrees
< ±1.3
dB
< ±0.45
Baseband I and Q Amplitude
Balance
Baseband I and Q Phase Accuracy
MHz
70
160
f
LO
Oscillator Frequency Range
MHz
9
BW
3dB
I and Q Signal 3dB Bandwidth
dB
51
Voltage Conversion Gain
Vp-p
1.35
Allowable I and Q Voltage Swing
dBc
-44
IM3
I/Q
I and Q IM3 Level
dBc
-60
IM5
I/Q
I and Q IM5 Level
UNITS
MIN
TYP
MAX
SYMBOL
PARAMETER
R
L
= 10k
, C
L
< 6pF
Vp-p
0.35
V
PRE_OUT
PRE_OUT Output Voltage
Offset = 10kHz
dBc/Hz
-80
Oscillator Phase Noise
R
L
= 10k
, C
L
< 6pF, rising edge
V/µs
60
SR
PRE_OUT
PRE_OUT Slew Rate
mV
±11
±50
Baseband I and Q DC Offset
dB
18
NF
Noise Figure
MAX2451
3V, Ultra-Low-Power
Quadrature Demodulator
_______________________________________________________________________________________
3
5.2
5.4
5.6
5.8
6.0
6.2
6.4
SUPPLY CURRENT
vs. TEMPERATURE
MAX2451-01
TEMPERATURE (°C)
I
CC
(mA)
10
20
30
40
50
60
70
0
V
CC
= 3.0V
0
1
2
3
4
5
6
7
SHUTDOWN SUPPLY CURRENT
vs. TEMPERATURE
MAX2451-02
TEMPERATURE (°C)
SHUTDOWN I
CC
(
µ
A)
10
20
30
40
50
60
70
0
V
CC
= 3.0V
48.0
48.5
49.0
49.5
50.0
50.5
51.0
51.5
VOLTAGE CONVERSION GAIN vs.
TEMPERATURE AND SUPPLY VOLTAGE
MAX2451-03
GAIN (dBV)
2.6
2.7
2.8
2.9 3.0
3.1
3.2
3.3
3.4
V
CC
(V)
T
A
= +50°C
T
A
= +25°C
T
A
= 0°C
T
A
= +70°C
42
52
51
50
49
48
47
46
45
44
43
VOLTAGE CONVERSION
GAIN vs. IF FREQUENCY
MAX2451-04
IF FREQUENCY (MHz)
GAIN (dBV)
500
400
300
200
100
0
f
BASEBAND
= 100kHz
V
LO_INJECT
= 40mV
RMS
= 113mVp-p
into 5O
V
IF_IN
= 2.82mV
P-P
0.4
0.8
0.6
1.0
1.2
1.4
1.6
PHASE AND AMPLITUDE
MATCHING vs. TEMPERATURE
MAX2451-05
TEMPERATURE (°C)
MATCHING (DEGREES OR dBV)
0
10
70
60
50
40
30
20
PHASE MATCH
AMPLITUDE MATCH
-65
-60
-55
-50
-45
-40
INTERMODULATION POWER
vs. TEMPERATURE
MAX2451-06
TEMPERATURE (°C)
INTERMODULATION (dBc)
0
10
70
60
50
40
30
20
IM3
IM5
f
LO
= 140MHz
f
IF1
= 70.10MHz
f
IF2
= 70.11MHz
V
IF_IN
= 1.41mVp-p per tone
PRE_OUT WAVEFORM
MAX2451-07
20ns/div
R
L
= 10k
C
L
< 6pF
100mV/div
__________________________________________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.)
_______________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).
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 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.
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 10k
. 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.
MAX2451
3V, Ultra-Low-Power
Quadrature Demodulator
4
_______________________________________________________________________________________
_____________________Pin Description
NAME
FUNCTION
1
IF
IF Input
2, 3, 16
GND
Ground
PIN
4
N.C.
No Connect. No internal connec-
tion to this pin.
5
ENABLE
Enable Control, active high
6
PRE_OUT
Local-Oscillator Divide-by-8
Prescaled Output
7
LO_V
CC
Local-Oscillator Supply. Bypass
separately from V
CC
.
8
TANK
Local-Oscillator Resonant Tank
Input
9
TANK
Local-Oscillator Resonant Tank
Inverting Input
10
LO_GND
Local-Oscillator Ground
11
Q
Baseband Quadrature Inverting
Output
12
Q
Baseband Quadrature Output
13
I
Baseband Inphase Inverting
Output
14
I
Baseband Inphase Output
15
V
CC
Demodulator Supply
2
A/D
A/D
÷8
POST
PROCESSING
DOWNCONVERTER
MAX2451
2
90°
0°
Figure 1. Typical Application Block Diagram
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.
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.
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.
__________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-
cation requirements. The oscillation frequency can be
determined using the following formula:
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:
where R
EQ
10k
(Figure 2).
The oscillation frequency can be changed by altering
the control voltage, V
CTRL
.
MAX2451
3V, Ultra-Low-Power
Quadrature Demodulator
_______________________________________________________________________________________
5
Figure 2. Local-Oscillator Equivalent Circuit
R
L
5k
R
L
5k
Q1
Q3
Q4
TO QUADRATURE
GENERATOR AND
PRESCALER
Q2
TANK
TANK
LO_V
CC
Figure 3. Typical Resonant Tank Circuit
L = 100nH
C2 = 33pF
C1 = 33pF
47k
10k
47k
1/2 KV1410
1/2 KV1410
TANK
TANK
V
CTRL
0.1
µ
F
f
1
2
L
C
where
C
1
1
C1
1
C2
2
C
C
and
L
L L
o
EQ EQ
EQ
VAR
STRAY
EQ
STRAY
=
=
+
+
+
= +
Q
R
EQ
CEQ
LEQ
=
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