Datasheet MAX2450CEP Datasheet (Maxim)

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General Description

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 400Ω 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 1µA. 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.

Applications

Digital Cordless Phones
GSM and North American Cellular Phones
Wireless LANs
Digital Communications
Two-Way Pagers

____________________________Features

♦ Combines Quadrature Modulator and

Demodulator

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

Circuit)

♦ On-Chip Divide-by-8 Prescaler
♦ Modulator Input Bandwidth Up to 15MHz
♦ Demodulator Output Bandwidth Up to 9MHz
♦ 51dB Demodulator Voltage Conversion Gain
♦ CMOS-Compatible Enable
♦ 5.9mA Operating Supply Current

1µA Shutdown Supply Current

MAX2450

3V, Ultra-Low-Power Quadrature

Modulator/Demodulator

________________________________________________________________

Maxim Integrated Products

1

ENABLEGND

400Ω

2

IF_OUT

1

83, 19

IF_OUT

9

PRE_OUT

14

Q_OUT

15

Q_OUT

16

I_OUT

17

I _OUT

20

IF_IN

10

LO_V

CC

11

TANK

12

TANK

4

I_IN

5

I_IN

6

Q_IN

7

Q_IN

18

V

CC

13

LO_GND

BIAS

PRESCALER

MODULATOR

DEMODULATOR

QUADRATURE

PHASE

GENERATOR

LOCAL

OSCILLATOR

÷ 2 ÷ 4

BANDGAP BIAS

MASTER BIAS

÷ 2

Σ

0°

90°

MAX2450

Functional Diagram

20
19
18
17
16
15
14
13

1
2
3
4
5
6
7
8

IF_IN
GND
V

CC

I_OUT
I_OUT
Q_OUT
Q_OUT
LO_GND
TANK
TANK

IF_OUT
IF_OUT

GND

I_IN

I_IN
Q_IN
Q_IN

ENABLE

PRE_OUT

LO_V

CC

TOP VIEW

12
11

9

10

QSOP

MAX2450

Pin Configuration

19-0455; Rev 1; 9/98

PART

MAX2450CEP 0°C to +70°C

TEMP. RANGE PIN-PACKAGE

EVALUATION KIT

AVAILABLE

Ordering Information

20 QSOP

MAX2450

3V, Ultra-Low-Power Quadrature
Modulator/Demodulator

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

DC ELECTRICAL CHARACTERISTICS

(VCC= LO_VCC= TANK = 2.7V to 3.3V, ENABLE = V

CC

- 0.4, GND = LO_GND = 0V, I_IN = I_IN = Q_IN = Q_IN = IF_IN = TANK =

OPEN, T

A

= 0°C to +70°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.

VCC, LO_VCCto 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 (T

A

= +70°C)

QSOP (derate 9.1mW/°C above +70°C)......................727mW

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

ENABLE = V

CC

CONDITIONS

V1.2

V

I_OUT/I_OUT

,

V

Q_OUT/Q_OUT

I_OUT, I_OUT, Q_OUT, Q_OUT
DC Bias Voltage Level

µA220I

CC(OFF)

Shutdown Supply Current

mA5.9 8.2I

CC(ON)

V2.7 3.3VCC, LO_V

CC

Supply Voltage Range
Supply Current

Ω320 400 480Z

IF_IN

Demodulator IF Input Impedance

VVCC- 1.5V

IF_OUT/IF_OUT

IF_OUT, IF_OUT DC Bias Voltage

kΩ35 44

Z

I_IN/I_IN

,

Z

Q_IN/Q_IN

Modulator Differential Input
Impedance

V1.25 1.5 1.75

V

I_IN/I_IN

,

V

Q_IN/Q_IN

I_IN, I_IN, Q_IN, Q_IN
Self-Bias DC Voltage Level

µs10t

ON/OFF

Enable/Disable Time

µA13I

EN

ENABLE Bias Current

VVCC- 0.4V

ENH

ENABLE High Voltage

V0.4V

ENL

ENABLE Low Voltage

UNITSMIN TYP MAXSYMBOLPARAMETER

AC ELECTRICAL CHARACTERISTICS

(MAX2450 EV kit, VCC= LO_VCC= ENABLE = 3.0V, fLO= 140MHz, f

I_IN/I_IN

= f

Q_IN/Q_IN

= 600kHz, V

I_IN/I_IN

= V

Q_IN/Q_IN

= 1.2V

p-p

,

f

IF_IN

= 70.1MHz, V

IF_IN

= 2.82mV

p-p

, TA= +25°C, unless otherwise noted.)

(Note 2)

(Note 2)

CONDITIONS

dB< ±0.45I and Q Amplitude Balance

dBc-60IM5

I/Q

I and Q IM5 Level

dBc-44IM3

I/Q

I and Q IM3 Level

degrees< ±1.3I and Q Phase Accuracy

dB51Voltage Conversion Gain

UNITSMIN TYP MAXSYMBOLPARAMETER

RL= 10kΩ, CL< 6pF, rising edge

(Notes 1, 3)
10kHz offset
RL= 10kΩ, CL< 6pF

MHz9BW

DEMOD

I and Q Signal 3dB Bandwidth

V/µs60SR

PRE_OUT

PRE_OUT Slew Rate

MHz70 160f

LO

Oscillator Frequency Range

dBc/Hz-80LO Phase Noise

V

p-p

0.35V

PRE_OUT

PRE_OUT Output Voltage

(Note 1) V

p-p

1.35Allowable I and Q Voltage Swing

mV±11 ±50

Demodulator I and Q Baseband
DC Offset

dB18NFNoise Figure

DEMODULATOR

MAX2450

3V, Ultra-Low-Power Quadrature

Modulator/Demodulator

_______________________________________________________________________________________

3

7.0

6.8

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 80

MAX2450-01

TEMPERATURE (°C)

SUPPLY CURRENT (mA)

SUPPLY CURRENT

vs. TEMPERATURE

V

CC

= 2.7V

V

CC

= 3.3V

V

CC

= 3.0V

0

2

4

6

8

10

12

0

10

20 30 40

50

60 70 80

MAX2450-02

TEMPERATURE (°C)

V

CC

= 2.7V

V

CC

= 3.3V

V

CC

= 3.0V

SHUTDOWN SUPPLY CURRENT

vs. TEMPERATURE

SUPPLY CURRENT (µA)

-30

-34

-38

-42

-46

-50

-54

-26 -22 -18 -14 -10 -6

MAX2450-03

BASEBAND INPUT (dBV

RMS

)

OUTPUT (dBV

RMS

)

MODULATOR IF OUTPUT

vs. BASEBAND INPUT

Vp-p = 2 2 x 10 (V)

dBV

RMS

20

(Note 1)

V

I_IN/I_IN

, = V

Q_IN/Q_IN = 1.2Vp-p,

RL= 200kΩ differential,
CL< 5pF differential

V

I_IN/I_IN

= 1.35Vp-p composite

(Note 4)
V

I_IN/I_IN

= 1.35Vp-p composite

(Note 4)

CONDITIONS

V1.25 1.75Input Common-Mode Voltage Range

V

p-p

1.35

V

I_IN/I_IN

,

V

Q_IN/Q_IN

Allowable Differential Input Voltage

dBc-36

Carrier Suppression at Modulator
Output

dBc38Sideband Rejection

MHz15BW

MOD

I and Q Signal 3dB Bandwidth

mV

p-p

65V

IF_OUT/IF_OUT

IF Differential Output Voltage

dBc-60IM3

IF

IF Output IM3 Level

dBc-60IM5

IF

IF Output IM5 Level

UNITSMIN TYP MAXSYMBOLPARAMETER

AC ELECTRICAL CHARACTERISTICS (continued)

(MAX2450 EV kit, VCC= LO_VCC= ENABLE = 3.0V, fLO= 140MHz, f

I_IN/I_IN

= f

Q_IN/Q_IN

= 600kHz, V

I_IN/I_IN

= V

Q_IN/Q_IN

= 1.2V

p-p

,

f

IF_IN

= 70.1MHz, V

IF_IN

= 2.82mV

p-p

, TA= +25°C, unless otherwise noted.)

MODULATOR

Note 1: Guaranteed by design, not tested.
Note 2: f

IF_IN

= 2 tones at 70.10MHz and 70.11MHz. V

IF_IN

= 1.41mVp-p per tone.

Note 3: 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. f

I_IN/I_IN

= 2 tones at 550kHz and 600kHz.

__________________________________________Typical Operating Characteristics

(MAX2450 EV kit, VCC= LO_VCC= ENABLE = 3.0V, fLO= 140MHz, f

I_IN/I_IN

= f

Q_IN/Q_IN

= 600kHz, V

I_IN/I_IN

= V

Q_IN/Q_IN

= 1.2V

p-p

,

f

IF_IN

= 70.1MHz, V

IF_IN

= 2.82mV

p-p

, TA= +25°C, unless otherwise noted.)

MAX2450

3V, Ultra-Low-Power Quadrature
Modulator/Demodulator

4 _______________________________________________________________________________________

____________________________Typical Operating Characteristics (continued)

(MAX2450 EV kit, VCC= LO_VCC= ENABLE = 3.0V, fLO= 140MHz, f

I_IN/I_IN

= f

Q_IN/Q_IN

= 600kHz, V

I_IN/I_IN

= V

Q_IN/Q_IN

= 1.2V

p-p

,

f

IF_IN

= 70.1MHz, V

IF_IN

= 2.82mV

p-p

, TA= +25°C, unless otherwise noted.)

60

62

64

66

68

70

MODULATOR IF OUTPUT

vs. SUPPLY VOLTAGE

MAX2450-04

VCC (V)

IF OUTPUT (mVp-p)

3.33.23.13.02.92.82.7

TA = +70°C

TA = +25°C

TA = 0°C

60

62

64

66

68

70

MODULATOR IF OUTPUT

vs.TEMPERATURE

MAX2450-05

TEMPERATURE (°C)

IF OUTPUT (mVp-p)

020406080

V

CC

= 3V

-44

-42

-40

-38

-36

-34

-32

-30

MODULATOR SIDEBAND REJECTION

vs. IF FREQUENCY

MAX2450-06

IF FREQUENCY (MHz)

SIDEBAND REJECTION (dBc)

35 40

706560555045

75 80

V

I_IN/I_IN

= 1.2Vp-p

V

Q_IN/Q_IN

= 1.2Vp-p

-44

-42

-40

-38

-36

MODULATOR SIDEBAND REJECTION

vs. TEMPERATURE

MAX2450-07

TEMPERATURE (°C)

SIDEBAND REJECTION (dBc)

020406080

V

I_IN/I_IN

= 1.2Vp-p

V

Q_IN/Q_IN

= 1.2Vp-p

-44

-42

-40

-38

-36

-34

-32

-30

CARRIER SUPPRESSION

vs. IF FREQUENCY

MAX2450-08

IF FREQUENCY (MHz)

CARRIER SUPPRESSION (dBc)

35 40

706560555045

75 80

V

I_IN/I_IN

= 1.2Vp-p

V

Q_IN/Q_IN

= 1.2Vp-p

100mV/

div

PRE_OUT WAVEFORM

MAX2450-09

20ns/div

RL = 10kΩ
C

L

< 6pF

-60

69.0 70.6

71.0

MODULATOR OUTPUT SPECTRUM

-50

0

MAX2450-10

(MHz)

(dBc)

69.4 70.0

-20

-10

-30

-40

V

I_IN/I_IN

= 1.2Vp-p

V

Q_IN/Q_IN

= 1.2Vp-p

MAX2450

3V, Ultra-Low-Power Quadrature

Modulator/Demodulator

_______________________________________________________________________________________

5

48.0

48.5

49.0

49.5

50.0

50.5

51.0

51.5

DEMODULATOR VOLTAGE CONVERSION

GAIN vs. TEMPERATURE AND SUPPLY

MAX2450-11

GAIN (dBV)

2.6 2.7 2.8 2.9 3.0 3.1 3.2 3.3 3.4
VCC (V)

TA = +50°C

TA = +25°C

TA = 0°C

TA = +70°C

50.6

50.8

51.0

51.2

51.4

DEMODULATOR VOLTAGE CONVERSION

GAIN vs. IF FREQUENCY

MAX2450-12

IF FREQUENCY (MHz)

GAIN (dBV)

35 40

706560555045

75 80

51
50

49
48
47
46
45
44
43
42

DEMODULATOR VOLTAGE CONVERSION

GAIN vs. BASEBAND FREQUENCY

MAX2450-13

BASEBAND FREQUENCY (Hz)

GAIN (dBV)

100M10M1M100k10k

____________________________Typical Operating Characteristics (continued)

(MAX2450 EV kit, VCC= LO_VCC= ENABLE = 3.0V, fLO= 140MHz, f

I_IN/I_IN

= f

Q_IN/Q_IN

= 600kHz, V

I_IN/I_IN

= V

Q_IN/Q_IN

= 1.2V

p-p

,

f

IF_IN

= 70.1MHz, V

IF_IN

= 2.82mV

p-p

, TA= +25°C, unless otherwise noted.)

0.4

0.8

0.6

1.0

1.2

1.4

1.6

DEMODULATOR I/Q PHASE

AND AMPLITUDE MISMATCH

vs. TEMPERATURE

MAX2450-15

TEMPERATURE (°C)

MATCHING (DEGREES OR dBV)

010

706050403020

PHASE MATCH

AMPLITUDE MATCH

-65

-60

-55

-50

-45

-40

DEMODULATOR INTERMOD POWER

vs. TEMPERATURE

MAX2450-16

TEMPERATURE (°C)

INTERMODULATION (dBc)

010

706050403020

IM3

IM5

f

OSC

= 140MHz

f

IF1

= 70.1MHz

f

IF2

= 70.11MHz

V

IF_IN

= 2.82mVp-p

MAX2450

3V, Ultra-Low-Power Quadrature
Modulator/Demodulator

6 _______________________________________________________________________________________

______________________________________________________________Pin Description

Local-Oscillator, Divide-by-8, Prescaled OutputPRE_OUT9
Local-Oscillator Supply. Bypass separately from VCC.LO_V

CC

10

Local-Oscillator Resonant Tank Input (Figure 4)TANK11
Local-Oscillator Resonant Tank Inverting Input (Figure 4)

TANK

12

Local-Oscillator GroundLO_GND13

Baseband Inphase Inverting InputI_IN5
Baseband Quadrature InputQ_IN6
Baseband Quadrature Inverting InputQ_IN7
Enable Control, active highENABLE8

Baseband Inphase InputI_IN4

GroundGND3, 19

PIN

Modulator IF Inverting OutputIF_OUT2

Modulator IF OutputIF_OUT1

FUNCTIONNAME

Demodulator Inphase Inverting OutputI_OUT16
Demodulator Inphase OutputI_OUT17
Modulator and Demodulator SupplyV

CC

18

Demodulator IF InputIF_IN20

Demodulator Quadrature Inverting OutputQ_OUT14
Demodulator Quadrature OutputQ_OUT15

Figure 1. Typical Application Block Diagram

2

A/D

CONVERSION

÷ 8

UP/DOWNCONVERTER

Σ

0°

90°

MAX2450

2

A/D

CONVERSION

2

D/A

CONVERSION

2

D/A

CONVERSION

R

T

DSP

_______________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 400Ω 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.

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,

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.

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 0.35V

p-p

with a 10kΩ and 6pF load. It can be

AC-coupled to the input of a frequency synthesizer.

Modulator

The modulator accepts I and Q differential baseband
signals up to 1.35V

p-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 44kΩ). The self-bias design yields very
low on-chip offset, resulting in excellent carrier sup-

MAX2450

3V, Ultra-Low-Power Quadrature

Modulator/Demodulator

_______________________________________________________________________________________ 7

Figure 2. Local-Oscillator Equivalent Circuit

R

L

5k

R

L

5k

Q1

Q3 Q4

TO
QUADRATURE
GENERATOR AND
PRESCALER

Q2

TANKTANK

LO_V

CC

Figure 3. Modulator Output Level vs. Load Resistance

35

40

45

50

55

60

65

70

75

MAX2450-fig03

LOAD RESISTANCE (Ω)

OUTPUT LEVEL (mVp-p)

200

1k 10k 100k

MAX2450

3V, Ultra-Low-Power Quadrature
Modulator/Demodulator

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

© 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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 (0.1µF) to GND.

The IF output is designed to drive a high impedance
(> 20kΩ), such as an IF buffer or an upconverter
mixer. IF_OUT/IF_OUT must be AC coupled to the
load. Impedances as low as 200Ω 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.

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
2µA. The master bias section includes a bandgap ref­erence generator and a PTAT (Proportional To Absolute
Temperature) current generator.

__________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:

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 phase­noise performance keep the Q of the resonant tank as
high as possible:

where R

EQ

≈ 10kΩ (Figure 2).

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

CTRL

.

QR

EQ

C

L

EQ
EQ

=

f

1

2LC

where
C

1

1C11

C22C

C

and

L L L

o

EQ EQ

EQ

VAR

STRAY

EQ STRAY

=

=

++

+

=+

π

Figure 4. Typical Resonant Tank Circuit

L = 100nH

C2 = 33pF

C1 = 33pF 47k

10k

47k

1

/2 KV1410

1

/2 KV1410

TANK

TANK

V

CTRL

0.1µF