Datasheet RF2721, RF2721PCBA Datasheet (RF Micro Devices)

2-27

7

QUADRATURE

DEMODULATORS

Preliminary

Product Description

Ordering Information

Typical Applications

Features

Functional Block Diagram

RF Micro Devices, Inc.
7628 Thorndike Road
Greensboro,NC 27409, USA

Tel [phone]

Fax [phone]

http://www.rfmd.com

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SiGe HBT

Si CMOS

1

2

3

4

5

6

7

14

13

12

11

10

9

8

IF1+

GND

OSCB

OSCE

GND

LO2-

LO2+

IF IN-

VCC

PD

GND

I OUT

REF IN

Q OUT

QUAD

DIV.

BY 2

POWER

CONTROL

5kΩ

5kΩ

RF2721

QUADRATURE DEMODULATOR

• UHF Digital and Analog Receivers

• Digital Communication Systems

• Spread-Spectrum Communication Systems

• Commercial and Consumer Systems

• Portable Battery-Powered Equipment

• General Purpose Frequency Conversion

The RF2721 is a monolithic integrated quadrature
demodulator intended for use in digital mobile radio
receivers. In this application it is used to recover the in­phase and quadrature baseband signals from the ampli­fied and filtered IF. The RF2721 is intended for IF sys­tems where the IF frequency ranges from 100kHz to
500 MHz, and the LO frequency is two times the IF. The
IC contains all of the required components to implement
the demodulation function of the receiver and contains a
digital divider type 90° phase shifter, two double-balanced
mixers, and baseband amplifiers designed to interface
with analog to digital converters. The output DC offset
maybeslavedtothereferenceoftheADCstomaintain
DC accuracy.

• 5V Power Supply

• On-Chip Active Device for Oscillator

• ADC Compatible Outputs

• Low LO Power Requirement

• Digitally Controlled Power Down Mode

• 100kHz to 500MHz IF Operation

RF2721 Quadrature Demodulator
RF2721 PCBA Fully Assembled EvaluationBoard

2

Rev A2 010509

0.156

0.148

0

.

0

5

9

0

.

0

5

7

0

.

2

5

2

0

.

2

3

6

0

.

0

1

0

0

.

0

0

4

.

0

1

8

.

0

1

4

8° MAX

0° MIN

0.0500

0.0164

0.010

0.007

0.347

0.339

0.050

Package Style: SOIC-14

Preliminary

2-28

RF2721

Rev A2 010509

7

QUADRATURE

DEMODULATORS

Absolute Maximum Ratings

Parameter Rating Unit

Supply Voltage -0.5 to +7.0 V

DC

Power Down Voltage(VPD) -0.5toV

CC

V

DC

IF Input Level 2.0 V

PP

LO Input Power +10 dBm
Operating Ambient Temperature -40 to +85 °C
Storage Temperature -40 to +150 °C

Parameter

Specification

Unit Condition

Min. Typ. Max.

Overall

T=25°C, VCC=5.0V

IF Frequency Range 0.1 to 500 MHz
Baseband Frequency Range DC to >10 MHz Load Impedance >5kΩ, C

SHUNT

<1pF

DC to 1 MHz Load Impedance >5kΩ, C

SHUNT

<10pF

Input Impedance 3 kΩ At 70MHz, each inpu t
Output Impedance 5000 Ω
Maximum Output >1.25 V

PP

With 250mV input

Gain 13 14 dB Small-signal, 100mV input
I/Q Amplitude Balance 0.1 0.5 dB
I/Q Phase Accuracy ±1 ±5 °
Reference Voltage 1.5 to 3.5 V The reference voltage input should providea

low impedance at the I/Q frequency. The
voltage sets the DC level seen onthe I and
Q ports.

DC Offset 3 20 mV I to Q

320mVIorQtoREFIN

LO

Oscillator Use provided transistor or external LO.
Frequency Twice (2x) the IF frequency.
Level 0.1-1 V

PP

Input Impedance 400-j1200 Ω At 140MHz

Power Down

Turn On/Off Time <100 ns
Input Resistance >50 kΩ
V

IH

2.5 V

CC

V Threshold voltage; Part is “ON”.

V

IL

0 0.8 V Threshold voltage; Part is “OFF”.

Power Supply

Voltage 5 V Specifications

4.5 to 5.5 V Operating limits

Current 4.5 7.2 mA Operating

300 500 µA Power Down

Caution! ESD sensitive device.

RF Micro Devices believes thefurnished information is correct and accurate
at the time of this printing. However, RF Micro Devices reserves the right to
make changes to its products without notice. RF Micro Devices does not
assume responsibility for the use of the described product(s).

Preliminary

2-29

RF2721

Rev A2 010509

7

QUADRATURE

DEMODULATORS

Pin Function Description Interface Schematic

1IFIN+

Balanced IF input. An input level of 400mVPPgives full output swing; a
level of maximum 250mV

PP

is recommended for linear operation. This

pin has no internal DC block, and an external capacitor of 100nF is
needed if con nected to a DC path.

2GND

Ground connection. For best performance, keep traces physically short
and connect immediately to ground plane.

3OSCB

Base of the LO transistor. This pin is not connected to anything else.
This transistor can be used for an oscillator.The collectorof the transis­tor is connected to V

CC

.

4OSCE

Emitter of the LO transistor. This pin is not connected to anything else. See pin 3.

5GND

Same as pin 2.

6LO2-

Balanced input for the doubled LO. An internal divide-by-2 network
generates the actual LO for the mixers. The divided signal is not acces­sible. When the LO is driven single ende d this pin should be connected
to a 100nFcapacitor to ground. This pin has an internal pull-up resistor
to V

CC

and an external DC blocking capacitor of 100nF is recom-

mended.

7LO2+

Balanced input for the doubled LO. The input frequency should be
twice (2x) the IF frequency.An internal divide-by-2 ne twork generates
the actual LO for the mixers. This pin has an internal pull-up resistor to
V

CC

, and an external DC blockingcapacitor of100nF is recommended.

LO frequencies below 100kHz are acceptable, providing that the LO
signal is square wave. Above 100kHz asine wavesignal is acceptable.
The quadrature accuracy of the LO/2 frequency into the mixers is
affected by the duty cycle of the LO input signal. Square wavesi gnals
with other than 50% duty cycle will degrade the quadrature accuracy of
the LO signal, thereby adversely affecting the I and Q quadrature accu­racy. Since the LO input is AC coupled, asymmetric sine waves and
sine waves clipped on either the top or bottom half will not have 50%
duty cycles relative to the internal DC reference point. For this reason,
distorted LO sine wave signals will degrade performance in a fashion
similar to non-50% duty cycle square waves. A sine waveinpu t with
even harmonics less than -15dB c is recommended. The internal limit­ing buffer amplifier ensures the amplitude stability of the demodulator.

See pin 6.

8QOUT

Demodulated baseband Q output. The referenc e DC level of this pin is
set by the voltage of pin 9 (REF IN), which is connected to this pin
througha5kΩ resistor to the collectors of this push-pull output. This
results in an output impedance of 5kΩ if the REF IN pin is connected to
a low impedance source. The capacitance of the load determines the
maximum baseband frequency. A very low capacitive load may stretch
the 3dB bandwidth over 10MHz. Another way to increase bandwidth is
by connecting a shunt resistor. This will trade-off gain for bandwidth.

9REFIN

Reference voltage input for the baseband outputs. This pin can be con­nected to the reference voltage source of the Analog to Digital Con­verter. It is connected to the I and Q outputs through 5kΩ resistors.
This pin should have an external decoupling capacitor large enough to
decouple the lowest baseband frequency.

See pin 8.

IF IN-

1500 Ω

IF IN+

1500 Ω

350 Ω350 Ω

VCC

OSC B
OSC E

200 Ω

200 Ω

LO2+

LO2-

5kΩ

REF IN
I/Q OUT

Preliminary

2-30

RF2721

Rev A2 010509

7

QUADRATURE

DEMODULATORS

Pin Function Description Interface Schematic

10 I OUT

Demodulated baseband I output. The reference DC level of this pin is
set by the voltage of pin 9 (REF IN), which is connected to this pin
through a 5kΩ resistor to the collectors of this push-pull output. This
results in an output impedance of 5kΩ if the REF IN pin is connected to
a low impedance source. The capacitance of the load determines the
maximum baseband frequency. A very low capacitive load may stretch
the 3dB bandwidth over 10MHz. Another way to inc rease bandwidth is
by connecting a shunt resistor. This will trade gain for bandwidth.

See pin 8.

11 GND

Same as pin 2.

12 PD

Power down control. When this pin is "low", all circuits are shut off. A
"low" is typically 0.8V or less at room temperature. When this pin is
"high", all circuits are operating normally.

13 VCC

Power supply pin. An external 100nF bypass capacitor is recom­mended if no other bypass capacitor is nearby.

14 IF IN-

Balanced IF input. An input level of 400mVPPgives full output swing; a
level of maximum 250mV

PP

is recommended for linear operation. This

pin has no internal DC block and an external capacitor of 100nF is
needed if c onnected to a DC path. If the IF is driven by a single-ended
source, connect this pin to an 100nF capacitor to ground.

See pin 1.

VCC

PD

Preliminary

2-31

RF2721

Rev A2 010509

7

QUADRATURE

DEMODULATORS

Evaluation Board Schematic

(Download Bill of Materials from www.rfmd.com.)

1

2

3

4

5

6

7

14

13

12

11

10

9

8

QUAD

DIV.

BY 2

POWER

CONTROL

C1

100 nF

R2

51 Ω

PD

5kΩ

5kΩ

C3

100 nF

R1

51 Ω

VCC

REF IN

J1

IF1

J2

LO IN

J3

I OUT

J4

Q OUT

2721400-

C2

100 nF

50 Ωµstrip

C7

100 nF

C4

100 nF

C5

100 nF

C6

100 nF

P2

1
2
3

CON3

NC

GND

P2-1 REF IN

P1

1
2
3

CON3

P1-1 VCC

GND

P1-3 PD

Preliminary

2-32

RF2721

Rev A2 010509

7

QUADRATURE

DEMODULATORS

Evaluation Board Layout

Board Thickness 1.5” x 1.5”

Board Thickness 0.031”, Board Material FR-4