Maxim MAX2451CSE Datasheet

19-0493; Rev 0; 12/95

EVALUATION KIT

AVAILABLE

3V, Ultra-Low-Power

Quadrature Demodulator

_______________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 400Ω 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 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

__________________Pin Configuration

TOP VIEW

IF
GND
GND

N.C.

ENABLE

PRE_OUT

LO_V

TANK

1
2
3

MAX2451

4
5
6



7

CC

8

SO

16
15
14
13
12

11
10

9

GND
V



CC

I



I
Q
Q
LO_GND
TANK

____________________________Features

♦ Integrated Quadrature Phase Shifters
♦ On-Chip Oscillator (Requires External Tuning

Circuit)

♦ 51dB Voltage Conversion Gain
♦ On-Chip Divide-by-8 Prescaler
♦ Baseband Output Bandwidth Up to 9MHz
♦ CMOS-Compatible Enable
♦ 5.5mA Operating Supply Current

2µA Shutdown Supply Current

______________Ordering Information

PART

MAX2451CSE 0°C to +70°C

TEMP. RANGE PIN-PACKAGE

16 Narrow SO

________________Functional Diagram

14

I

13

12

11

6

I

Q

Q

PRE_OUT

LO_V

TANK
TANK

LO_GND

V

1

IF

400Ω

7

CC

8
9

10

LOCAL

OSCILLATOR

15

CC

BANDGAP BIAS

DEMODULATOR

0°

÷ 2 ÷ 4

QUADRATURE

PHASE

GENERATOR

÷ 2

MASTER BIAS

PRESCALER

90°

52, 3, 16

ENABLEGND

BIAS

MAX2451

MAX2451

________________________________________________________________

Maxim Integrated Products

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.

1

3V, Ultra-Low-Power
Quadrature Demodulator

ABSOLUTE MAXIMUM RATINGS

VCC, LO_VCCto GND............................................-0.3V to +4.5V

ENABLE, TANK, TANK

to GND.............................................-0.3V to (VCC+ 0.3V)

Q, Q

IF to GND...............................................................-0.3V to +1.5V

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.

MAX2451

, I, I,

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,

= 0°C to +70°C, unless otherwise noted.)

T

A

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

VCC,

LO_V

CC(ON)

CC(OFF)

ON/OFF

EN
ENH
ENL

IN

V

I/

I

V

Q/Q

CC

Enable = 0.4V

,

Continuous Power Dissipation (T

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

CONDITIONS

= +70°C)

A

UNITSMIN TYP MAXSYMBOLPARAMETER

V2.7 3.3

mA5.5 7.4I

µA220I
µs10t
µA13I

VVCC- 0.4V
V0.4V
Ω320 400 480Z

V1.2

mV±11 ±50Baseband I and Q DC Offset

AC ELECTRICAL CHARACTERISTICS

VCC= LO_VCC= ENABLE = 3.0V, fLO= 140MHz, fIF= 70.1MHz, VIF= 2.82mVp-p, TA= +25°C, unless otherwise noted.)

CONDITIONS

Baseband I and Q Amplitude
Balance

Baseband I and Q Phase Accuracy

(Note 1)
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

Note 1: Guaranteed by design, not tested.
Note 2: f
Note 3: Oscillator frequencies up to 1GHz (500MHz IF) by externally overdriving (see

2 _______________________________________________________________________________________

= 2 tones at 70.10MHz and 70.11MHz, VIF= 1.41mVp-p per tone.

IF

LO

PRE_OUT

PRE_OUT

I/Q
I/Q

3dB

(Note 2)

(Note 2)

(Notes 1, 3)

RL= 10kΩ, CL< 6pF Vp-p0.35V

RL= 10kΩ, CL< 6pF, rising edge V/µs60SR

Offset = 10kHz dBc/Hz-80Oscillator Phase Noise

Applications Information

).

UNITSMIN TYP MAXSYMBOLPARAMETER

dB< ±0.45

degrees< ±1.3

dB51Voltage Conversion Gain
dB18NFNoise Figure

Vp-p1.35Allowable I and Q Voltage Swing

dBc-44IM3

dBc-60IM5
MHz9BW
MHz70 160f

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= +25°C, unless otherwise noted.)

6.4

6.2

6.0

(mA)

5.8

CC

I

5.6

5.4

5.2

52
51
50
49
48
47

GAIN (dBV)

46
45
44
43
42

SUPPLY CURRENT

vs. TEMPERATURE

V

= 3.0V

CC

10 20 30 40 50 60 700

TEMPERATURE (°C)

VOLTAGE CONVERSION

GAIN vs. IF FREQUENCY

f

= 100kHz

BASEBAND

= 40mV

V

LO_INJECT

into 5OΩ

= 2.82mV

V



IF_IN

P-P

IF FREQUENCY (MHz)

= 113mVp-p 

RMS

7

MAX2451-01

6

5

(µA)

CC

4

3

SHUTDOWN I

2

1

0

1.6

MAX2451-04

1.4

1.2

1.0

0.8

MATCHING (DEGREES OR dBV)

0.6

5004003002001000

0.4

SHUTDOWN SUPPLY CURRENT

vs. TEMPERATURE

V

= 3.0V

CC

10 20 30 40 50 60 700

TEMPERATURE (°C)

PHASE AND AMPLITUDE

MATCHING vs. TEMPERATURE

PHASE MATCH

AMPLITUDE MATCH

010

TEMPERATURE (°C)

MAX2451-02

MAX2451-05

706050403020

VOLTAGE CONVERSION GAIN vs.

TEMPERATURE AND SUPPLY VOLTAGE

51.5

51.0
TA = +25°C

50.5

50.0

49.5

GAIN (dBV)

49.0

48.5

48.0

2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4

-40

-45

-50
f

LO

f

IF1

-55

f

IF2

V

IF_IN

INTERMODULATION (dBc)

-60

-65

010

TA = 0°C

TA = +50°C

TA = +70°C

VCC (V)

INTERMODULATION POWER

vs. TEMPERATURE



IM3

= 140MHz

= 70.10MHz
= 70.11MHz

= 1.41mVp-p per tone

IM5

TEMPERATURE (°C)

706050403020

MAX2451

MAX2451-03

MAX2451-06

PRE_OUT WAVEFORM

MAX2451-07

100mV/div

RL = 10kΩ

< 6pF

C

L

20ns/div

_______________________________________________________________________________________

3

3V, Ultra-Low-Power
Quadrature Demodulator

_____________________Pin Description

PIN

1 IF IF Input

2, 3, 16 GND Ground

4 N.C.

MAX2451

5 ENABLE Enable Control, active high
6 PRE_OUT

7 LO_V

8 TANK

9 TANK
10 LO_GND Local-Oscillator Ground
11 Q
12 Q Baseband Quadrature Output
13 I
14 I Baseband Inphase Output

15 V

NAME FUNCTION

No Connect. No internal connec­tion to this pin.

Local-Oscillator Divide-by-8
Prescaled Output

Local-Oscillator Supply. Bypass

CC

separately from VCC.
Local-Oscillator Resonant Tank

Input
Local-Oscillator Resonant Tank

Inverting Input

Baseband Quadrature Inverting
Output

Baseband Inphase Inverting
Output

CC

Demodulator Supply

_______________Detailed Description

The following sections describe each of the functional
blocks shown in the
the Typical Application Block Diagram (Figure 1).

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 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.

Functional Diagram

Demodulator

. Also refer to

DOWNCONVERTER

2

0˚

90˚

MAX2451

÷8

Figure 1. Typical Application Block Diagram

A/D

2

A/D

POST

PROCESSING

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

2.2µH) is required between TANK and TANK. Differential
input impedance at TANK/TANK is 10kΩ. 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.

4 _______________________________________________________________________________________

LO_V

3V, Ultra-Low-Power

Quadrature Demodulator

MAX2451

CC

R

L

5k

Q3 Q4

Q1

Figure 2. Local-Oscillator Equivalent Circuit

R

L

5k

TANKTANK

Q2

TO QUADRATURE
GENERATOR AND

PRESCALER

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 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
VCC- 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 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-

C1 = 33pF 47k

TANK

1

/2 KV1410

L = 100nH

1

/2 KV1410

TANK

C2 = 33pF

Figure 3. Typical Resonant Tank Circuit

10k

47k

0.1µF
V

CTRL

cation requirements. The oscillation frequency can be
determined using the following formula:

f

o

=

2LC

π

EQ EQ

1

where
C

EQ

=

1C11

1

++

C22C

VAR

C

+

STRAY

and

L L L

where C

STRAY

=+

EQ STRAY

= parasitic capacitance and L

STRAY

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:

C

EQ

EQ

L

EQ

where R

QR

=

≈ 10kΩ (Figure 2).

EQ

The oscillation frequency can be changed by altering
the control voltage, V

CTRL

.

=

_______________________________________________________________________________________ 5

3V, Ultra-Low-Power
Quadrature Demodulator

________________________________________________________Package Information

INCHES MILLIMETERS

DIM

MAX2451

e



D

A

0.101mm

A1

B

0.004in.

C

0°-8°

L

Narrow SO

HE

SMALL-OUTLINE

PACKAGE

(0.150 in.)

A1

DIM

D
D
D

A

B
C
E

e

H

L

PINS



MAX

MIN

0.069

0.053

0.010

0.004

0.019

0.014

0.010

0.007

0.157

0.150

0.228

0.016

8
14
16





0.244

0.050

INCHES MILLIMETERS

MIN

MAX

0.189

0.197

0.337

0.344

0.386

0.394

MIN

1.35

0.10

0.35

0.19

3.80

5.80

0.40



MIN

4.80

8.55

9.80

1.270.050

MAX

1.75

0.25

0.49

0.25

4.00


6.20

1.27

MAX

5.00

8.75

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

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