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PDF RF2905 Data sheet ( Hoja de datos )
| Número de pieza | RF2905 | |
| Descripción | 433/868/915MHZ FM/FSK/ASK/OOK TRANSCEIVER | |
| Fabricantes | RF Micro Devices | |
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11
Typical Applications
• Wireless Meter Reading
• Keyless Entry Systems
• 433/868/915MHz ISM Band Systems
RF2905
433/868/915MHZ FM/FSK/ASK/OOK
TRANSCEIVER
• Wireless Data Transceiver
• Wireless Security Systems
• Battery Powered Portable Devices
Product Description
The RF2905 is a monolithic integrated circuit intended for
use as a low cost FM transceiver. The device is provided
in 7mmx7mm, 48-lead plastic LQFP packaging and is
designed to provide a fully functional FM transceiver. The
chip is intended for linear (AM, FM) or digital (ASK, FSK,
OOK) applications in the North American 915MHz ISM
band and European 433MHz and 868MHz ISM bands.
The integrated VCO, dual modulus/dual divide (128/129
or 64/65) prescaler, and reference oscillator require only
the addition of an external crystal to provide a complete
phase-locked oscillator.
Optimum Technology Matching® Applied
üSi BJT
GaAs HBT
GaAs MESFET
Si Bi-CMOS
SiGe HBT
Si CMOS
TX OUT 3
RX IN 5
LNA OUT 7
MIX IN 9
MIX OUT+ 11
MIX OUT- 12
47 34 31 30
41 42
43
Gain
Control
Phase
Detector &
Charge Pump
Lock
Detector
Prescaler
128/129 or
64/65
Linear
RSSI
40 39 38
Ref
Select
37 OSC SEL
45 PRESCL OUT
36 MOD CTRL
35 DIV CTRL
24 RSSI
25 FM OUT
26 DATA OUT
13 14 15 16 17 18 20 21 22 28 27
23
Functional Block Diagram
9.00
+ 0.20 sq.
7.00
+ 0.10 sq.
0.35
0.25
0.50
0.22
+ 0.05
7° MAX
0° MIN
1.40
+ 0.05
Dimensions in mm.
0.60
+ 0.15
0.10
0.127
Package Style: LQFP-48, 7x7
Features
• Fully Monolithic Integrated Transceiver
• 2.7V to 5.0V Supply Voltage
• Narrow Band and Wide Band FM/FSK
• 300MHz to 1000MHz Frequency Range
• 10dB Cascaded Noise Figure
• 10mW Output Power at 433MHz
Ordering Information
RF2905
433/868/915MHz FM/FSK/ASK/OOK Transceiver
RF2905 PCBA-L Fully Assembled Evaluation Board (433MHz)
RF2905 PCBA-M Fully Assembled Evaluation Board (868MHz)
RF2905 PCBA-H Fully Assembled Evaluation Board (915MHz)
RF Micro Devices, Inc.
7628 Thorndike Road
Greensboro, NC 27409, USA
Tel (336) 664 1233
Fax (336) 664 0454
http://www.rfmd.com
11
Rev B11 010516
11-53
1 page  
RF2905
Pin
1
Function
RX ENABL
Description
Enable pin for the receiver circuits. RX ENABL>2.0V powers up all
receiver functions. RX ENABL<1.0V turns off all receiver functions
except the PLL functions and the RF mixer.
Interface Schematic
RX ENABL
50 kΩ
2 TX ENABL Enables the transmitter circuits. TX ENABL>2.0V powers up all trans-
20 kΩ
mitter functions. TX ENABL<1.0V turns off all transmitter functions
TX ENABL
except the PLL functions.
40 kΩ
3 TX OUT RF output pin for the transmitter electronics. TX OUT output impedance
is a low impedance when the transmitter is enabled. TX OUT is a high
impedance when the transmitter is disabled.
4
GND2
Ground connection for the 40dB IF limiting amplifier and Tx PA func-
tions. Keep traces physically short and connect immediately to ground
plane for best performance.
5
RX IN
RF input pin for the receiver electronics. RX IN input impedance is a
low impedance when the transmitter is enabled. RX IN is a high imped-
ance when the receiver is disabled.
VCC
20
TX OUT
RX IN
500
6
GND1
Ground connection for RF receiver functions. Keep traces physically
short and connect immediately to ground plane for best performance.
7 LNA OUT Output pin for the receiver RF low noise amplifier. This pin is an open
collector output and requires an external pull up coil to provide bias and
tune the LNA output.
8
GND3
Same as pin 4.
9
MIX IN
RF input to the RF Mixer. An LC matching network between LNA OUT
and MIX IN can be used to connect the LNA output to the RF mixer
input in applications where an image filter is not needed or desired.
VCC
MIX IN
LNA OUT
GND5
10
GND5
GND5 is the ground connection shared by the input stage of the trans-
mit power amplifier and the receiver RF mixer.
11 MIX OUT+ Complementary (with respect to pin 12) IF output from the RF mixer. MIX OUT+
Interfaces directly to 10.7MHz ceramic IF filters as shown in the appli-
MIX OUT-
cation schematic. A pull-up inductor and series matching capacitor
should be used to present a 330Ω termination impedance to the
ceramic filter. Alternately, an IF tank can be used to tailor the IF fre-
quency and bandwidth to meet the needs of a given application.
15 pF
GND5
15 pF
GND5
12 MIX OUT- IF output from the RF mixer. For a balanced mixer output, pull-up induc- See pin 11.
tors from pin 11 and 12 to VCC and a capacitor between the pins should
be used. The sum of the total pull-up inductance should be used to res-
onate the capacitor between pins 11 and 12. DC blocking capacitors of
10nF can then be used to connect the balanced output to IF1 IN+ (pin
13) and IF1 IN- (pin 14).
11
Rev B11 010516
11-57
5 Page 
The quad tank of the discriminator can be implemented
with ceramic discriminators available from a couple of
sources. This design works well for wideband applica-
tions and where the temperature range is limited. The
temperature coefficient of a ceramic discriminator can
be in the order of +/- 50ppm per degree C. An auto-
matic frequency control loop can be implemented
using the DC level of the FM OUT for feedback to an
external varactor on the reference crystal. An alterna-
tive to the ceramic discriminator is a LC tank. Figure 2
shows a schematic implementation of a LC tank.
28
C17 7 pF
27
C16 10 nF
39 pF
3.3 µH
4-22
pF
R
opt.
Figure 2. LC Type Discriminator Circuit
The DEMOD IN pin has a DC bias on it and must be
DC blocked. This can be done either at the pin or at the
ground side of the LC tank (this must also be done if a
parallel resistor is used with a ceramic discriminator).
The decision whether to used a LC or a ceramic dis-
criminator should be based upon the frequency devia-
tion in the system, discriminator Q needed, and
frequency and temperature tolerances. Tuning of the
LC tank is required to overcome the component toler-
ances in the tank.
PREDICTING AND MINIMIZING PLL LOCK TIME
The RF2905 implements a conventional PLL on chip,
with a VCO followed by a prescaler dividing the output
frequency down to be compared with a signal from the
reference oscillator. The output of the phase discrimi-
nator is a sequence of pulse width modulated current
pulses in the required direction to steer the VCO’s con-
trol voltage to maintain phase lock, with a loop filter
integrating the current pulses. The lock time of this PLL
is a combination of the loop transient response time
and the slew rate set by the phase discriminator output
current combined with the magnitude of the loop filter
capacitance. A good approximation for total lock time
of the RF29.5 is:
Lock time=D/fc+35000*C*dV
Where D is a factor to account for the loop damping.
For loops with low phase margin (30° to 40°), use D=2
whereas for loops with better phase margin (50° to
60°), use D=1. fc is the loop cut frequency. C is the
sum of all shunt capacitors in the loop filter. dV is the
required step voltage change to produce the desired
frequency change during the transient.
Rev B11 010516
RF2905
To lock faster, we need to minimize C.
1. To this end, use the divide by 128 rather than the
64, and a correspondingly lower frequency refer-
ence crystal to achieve the desired output fre-
quency.
2. Design the loop filter for the minimum phase margin
possible without causing loop instability problems;
this allows C to be kept at a minimum.
3. Design the loop filter for the highest loop cut fre-
quency possible without distorting low frequency
modulation components; this also allows C to be
kept at a minimum.
CRYSTAL SELECTION
Several issues arise in the selection of the crystals.
Timing specifications such as start-up and switching
are related to the crystal specifications, as well as
external circuitry. The tolerance of the crystals are also
an issue in optimum radio performance. In general,
tighter tolerance crystals lead to better performance
and are more critical to higher data rates. Frequency
offsets between the TX crystal, RX crystal and discrim-
inator generate duty cycle variations in the receive
demodulator.
The crystals used on the RF2905 evaluation boards
are specified as a parallel resonant, 30pF crystal with
a maximum ESR of 80Ω. The initial tolerance is
+20ppm and temperature stability is +30ppm for -10°C
to 70°C. The transistor oscillator will work with a variety
of different crystals and the final crystal specifications
should be evaluated for each application.
11
Faster start-up or switching times are achievable by
specifying crystals with low motion inductance and low
motional resistance. Additionally, the feedback caps of
the oscillator can be changed to increase the voltage
on the crystal. Generally, crystals in the leaded
HC-49U packages will provide better start-up times
than the smaller surface-mount types used on the eval-
uation board.
11-63
11 Page | ||
| Páginas | Total 22 Páginas | |
| PDF Descargar | [ Datasheet RF2905.PDF ] | |
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