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Preliminary
Product Description
Ordering Information
Typical Applications
Features
Functional Block Diagram
RF Micro Devices, Inc.
7628 Thorndike Road
Greensboro, NC 27409, USA
Tel (336) 664 1233
Fax (336) 664 0454
http://www.rfmd.com
Optimum Technology Matching Applied
Si BJT
GaAs MESFET
GaAs HBT
Si Bi-CMOS
SiGe HBT
Si CMOS
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14
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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
5 k
5 k
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 in-
phase and quadrature baseband signals from the ampli-
fied and filtered IF. The RF2721 is intended for IF sys-
tems where the IF frequency ranges from 100kHz to
500MHz, 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
may be slaved to the reference of the ADCs to maintain
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 Evaluation Board
2
Rev A2 010509
0.156
0.148
0.059
0.057
0.252
0.236
0.010
0.004
.018
.014
8 MAX
0 MIN
0.0500
0.0164
0.010
0.007
0.347
0.339
0.050
Package Style: SOIC-14
Preliminary
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RF2721
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Absolute Maximum Ratings
Parameter
Rating
Unit
Supply Voltage
-0.5 to +7.0
V
DC
Power Down Voltage (V
PD
)
-0.5 to V
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 = 25C, V
CC
= 5.0V
IF Frequency Range
0.1 to 500
MHz
Baseband Frequency Range
DC to >10
MHz
Load Impedance > 5k
,
C
SHUNT
<1pF
DC to 1
MHz
Load Impedance > 5k
,
C
SHUNT
<10pF
Input Impedance
3
k
At 70MHz, each input
Output Impedance
5000
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 provide a
low impedance at the I/Q frequency. The
voltage sets the DC level seen on the I and
Q ports.
DC Offset
3
20
mV
I to Q
3
20
mV
I or Q to REF IN
LO
Oscillator
Use provided transistor or external LO.
Frequency
Twice (2x) the IF frequency.
Level
0.1-1
V
PP
Input Impedance
400- j1200
At 140MHz
Power Down
Turn On/Off Time
<100
ns
Input Resistance
>50
k
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
A
Power Down
Caution! ESD sensitive device.
RF Micro Devices believes the furnished 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
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Pin
Function
Description
Interface Schematic
1
IF IN+
Balanced IF input. An input level of 400mV
PP
gives 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 connected to a DC path.
2
GND
Ground connection. For best performance, keep traces physically short
and connect immediately to ground plane.
3
OSC B
Base of the LO transistor. This pin is not connected to anything else.
This transistor can be used for an oscillator. The collector of the transis-
tor is connected to V
CC
.
4
OSC E
Emitter of the LO transistor. This pin is not connected to anything else.
See pin 3.
5
GND
Same as pin 2.
6
LO2-
Balanced input for the doubled LO. An internal divide-by-2 network
generates the actual LO for the mixers. The divided signal is not acces-
sible. When the LO is driven single ended this pin should be connected
to a 100nF capacitor to ground. This pin has an internal pull-up resistor
to V
CC
and an external DC blocking capacitor of 100nF is recom-
mended.
7
LO2+
Balanced input for the doubled LO. The input frequency should be
twice (2x) the IF frequency. An internal divide-by-2 network generates
the actual LO for the mixers. This pin has an internal pull-up resistor to
V
CC
, and an external DC blocking capacitor of 100nF is recommended.
LO frequencies below 100kHz are acceptable, providing that the LO
signal is square wave. Above 100kHz a sine wave signal 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 wave signals
with other than 50% duty cycle will degrade the quadrature accuracy of
the LO signal, thereby adversely affecting the I and Q quadrature accu-
racy. 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 wave input with
even harmonics less than -15dBc is recommended. The internal limit-
ing buffer amplifier ensures the amplitude stability of the demodulator.
See pin 6.
8
Q OUT
Demodulated baseband Q 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 5k
resistor to the collectors of this push-pull output. This
results in an output impedance of 5k
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.
9
REF IN
Reference voltage input for the baseband outputs. This pin can be con-
nected to the reference voltage source of the Analog to Digital Con-
verter. It is connected to the I and Q outputs through 5k
resistors.
This pin should have an external decoupling capacitor large enough to
decouple the lowest baseband frequency.
See pin 8.
IF IN-
1500
IF IN+
1500
350
350
VCC
OSC B
OSC E
200
200
LO2+
LO2-
5 k
REF IN
I/Q OUT
Preliminary
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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 5k
resistor to the collectors of this push-pull output. This
results in an output impedance of 5k
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 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 recom-
mended if no other bypass capacitor is nearby.
14
IF IN-
Balanced IF input. An input level of 400mV
PP
gives 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 connected 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
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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
PD
5 k
5 k
C3
100 nF
R1
51
VCC
REF IN
J1
IF1
J2
LO IN
J3
I OUT
J4
Q OUT
2721400-
C2
100 nF
50
strip
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
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RF2721
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Evaluation Board Layout
Board Thickness 1.5" x 1.5"
Board Thickness 0.031", Board Material FR-4
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