Data Sheet
Doc. No. 100646A
Conexant Proprietary
January 19, 2000
RF109
2400 MHz Digital Spread Spectrum Transceiver
The RF109, a fully integrated transceiver device, provides the transmit, receive, and
frequency synthesis functions for 2400 MHz digital spread spectrum systems operating
in the 24002483.5 MHz portion of the ISM (Industrial, Scientific, Medical) band. The
device has a direct conversion architecture that minimizes circuit complexity and cost.
The receive path of the RF109 provides complete RF-to-baseband I/Q demodulation,
including an LNA, double-balanced quadrature mixers, fully integrated baseband filters,
and baseband variable-gain amplifiers. The transmit path is a variable-gain direct
conversion modulator. Figure 1 shows the RF109's pin signals. Figure 2 shows the
RF109 block diagram.
The RF109 generates the Local Oscillator (LO) frequencies using a Phase Lock Loop
(PLL) frequency synthesizer and an external 2.4 GHz Voltage Controlled Oscillator
(VCO). The PLL provides a full frequency range of 2392.22505.6 MHz.
The RF109 features low-voltage operation (3.04.5V) for low power consumption. A
complete RF system solution for 2.4 GHz cordless telephone applications can be
constructed with the RF109, a power amplifier, a differential 2.4 GHz frequency source
and a Transmit/Receive (T/R) switch.
RF109
1
2
3
4
5
6
7
8
12
9
10
11
36
35
34
33
32
31
30
29
25
28
27
26
13 14 15 16 17 18 19 20
24
21 22 23
48 47 46 45 44 43 42 41
37
40 39 38
STROBE
NC8
SYNTHEN
NC6
NC7
CHPO
VCC5
VCC6
VCO2
NC5
VCO1 NC4
CLK
NC1
FREF
TXD
VCC2
VCC1
TXREF
DATA
LNAATTN
RXEN
LNAIN
NC2
GND1
GMCRES
RFO1
MODSET
MIXBPC
TXEN
GND2
RFO2
PS2
PS1
GCREF
AGC
RXQ-
NC3
VCC3
SRI+
GND3
VCC4
SRQ-
SRQ+
SRI-
RXI-
RXI+
RXQ+
Figure 1. RF109 Pin Signals
Features
Low power dissipation
Fast settling from standby mode to active
mode
Separate enable lines for transmit, receive,
and synthesizer
64 programmable channels with 1.8 MHz
channel spacing
3-battery-cell operation
48-pin TQFP package with exposed paddle
(refer to Figure 6)
Receiver
-
LN
A/Quadrature mixer from RF down to
baseband
-
Selectable LNA gain
-
Integrated baseband filter with external
bandwidth adjustment
-
Receiver baseband amplifier with
automatic gain control
-
Direct conversion with differential
baseband outputs
-
Low system noise figure (9.0 dB typical)
-
Large dynamic range (89 dB typical)
Transmitter
-
Variable gain modulator
-
Mixer for baseband-to-RF modulation
-
Differential TX inputs and outputs
-
Selectable transmitter output levels for
high, medium, and low power modes
Applications
Digital Spread Spectrum (DSS) cordless
telephone
Direct sequence spread spectrum systems
Frequency hopping spread spectrum
systems
Wireless LANs
Wireless modems
Wireless security
Inventory control systems
RF109
2400 MHz Digital Spread Spectrum Transceiver
2
Conexant
100646A
Conexant Proprietary
1/19/00
LNAATTN
90
o
Synthesizer
LNAIN
Modulator
Gain
Control
RFO1
RFO2
LNA
FREF
GMCRES
RXQ
AGC
RXI
STROBE
CLK
DATA
TXD
External
CSERVO
MODSET
PS1
PS2
LPF
VCO
External
Serial
Interface
External
CSERVO
Power
Mgmt.
RXEN
SYNTHEN
TXEN
Figure 2. RF109 Block Diagram
Technical Description
Receive Path_______________________________________
The LNA provides two gain levels for coarse Automatic Gain
Control (AGC), which are selected via the LNAATTN control.
The signal is down-converted to In-phase and Quadrature-
phase (I/Q) baseband signals using a matched pair of mixers
and the LO.
The receive baseband bandwidth has a bandpass characteristic.
The I/Q baseband signals are internally low-pass and high-pass
filtered to attenuate out-of-channel signals and to remove DC
components. The low-pass cutoff is determined by the GmC
filters and is set by the R
gmc
resistor connected to pin 13. The
high-pass cutoff is set by the value of the C
servo
capacitors
connected between pins 3233, and pins 3435.
The baseband high-pass cutoff frequency should be set much
lower than the low-pass cutoff frequency or else the servo loop
will become unstable.
The optimum receive bandwidth values are:
f
LPF
= 820 kHz, R
gmc
= 825
f
HPF
= 20 kHz, C
servo
= 0.082
F
A matched pair of VGAs provide fine AGC. The differential I/Q
baseband signals are DC-coupled to the RXI+, RXI-, RXQ+, and
RXQ- outputs, respectively.
Transmit Path_______________________________________
The transmit path consists of an amplifier and a mixer. The
mixer modulates the LO with baseband data supplied to pin 8.
The transmit RF outputs from the RF109 are differential and
matched for a 100
differential load. If a single-ended
connection is required, then the unused output must be suitably
terminated by a 50
resistor (as shown in Figure 5).
The transmit output power is determined by the output power
control inputs, PS1 (pin 21) and PS2 (pin 22), and by the value
of R
mod
(connected to pin 20). R
mod
sets the bias current into the
modulator which is then multiplied by a factor set by the state of
PS1 and PS2. PS1 and PS2 input programming is given in the
Transmitter Section of Table 3.
LO Generation ______________________________________
The LO is generated by a programmable PLL frequency
synthesizer and a 2.4 GHz external VCO. Synthesizer
performance parameters are determined by the loop filter, the
external reference oscillator, the sensitivity and phase noise of
the VCO, and the frequency synthesizer programming.
The RF109 requires differential inputs for VCO1 (pin 38) and
VCO2 (pin 39). The typical differential input level is 200 mVp-p.
A BALUN transformer, shown in Figure 5, is used to generate
differential signals from a single-ended VCO output.
2400 MHz Digital Spread Spectrum Transceiver
RF109
100646A
Conexant
3
1/19/00
Conexant Proprietary
Synthesizer Programming____________________________
The frequency synthesizer block is comprised of a divide-by-3
counter (D), 9.6 MHz reference frequency (FREF) source, a
fixed reference divider of 16 (R), 16/17 prescaler (M), a fixed
counter of 83 (N), a programmable counter of 64 (A),an external
loop filter, and a 2.4 GHz external VCO.
The synthesizer can be programmed to cover 64 channels
(channel spacing = 1.8 MHz) from 2392.2 MHz to 2505.6 MHz
Table 1).
The LO frequency is given by the following equation:
f
LO
= (D) (FREF/R) ((M N) + (A + 1)), where N > A.
Example:
f
LO
= 3 (9.6 MHz / 16) ((16 83) + 7) = 2403.0 MHz
f
LO
= 3 (9.6 MHz / 16) ((16 83) + 46) = 2473.2 MHz
Data Format. The synthesizer is programmed with a half-
duplex 3-wire serial interface. The three signals are DATA, CLK,
and STROBE. Each rising edge of the CLK signal shifts one bit
of the data into a shift register. When the STROBE input is
toggled from low to high, the data latched in the shift register is
transferred to the A counter. The data format is as follows:
MSB
S7
S6
S5
S4
S3
S2
S1
S0
LSB
The timing relationship is shown in Figure 4. Programming bits
S0 to S5, used for the A counter, are defined in Table 1. Bits S6
and S7 are reserved.
Synthesizer Loop Filter. A typical loop filter design is shown
below in Figure 3. The loop bandwidth is approximately 5 kHz
with a nominal phase margin of 45 degrees for a VCO sensitivity
of 60 MHz/V.
0 . 0 1 F
1 0 k
V C O
T U N E
3 3 0
p F
3 9 0
p F
1 0 k
C H P O
pin 43
Figure 3. Typical Loop Filter
Power Management __________________________________
Independent power-up/power-down control of the transmit path,
receive path, and frequency synthesizer is provided by the
TXEN, RXEN and SYNTHEN controls, respectively. When all of
the functions are powered down, the current drain from the
voltage supply (Vcc) is at a minimum.
t1
t2
t3
t5
t4
M S B
L S B
D A T A
C L K
S T R O B E
t1 =Data setup time
t2 =Data hold time
t3 =Clock pulse-width
t4 =STROBE enable pulse-width
t5 =STROBE setup time to the rising edge of the last clock
t1 to t5 > 1s each
Figure 4. Timing Diagram
RF109
2400 MHz Digital Spread Spectrum Transceiver
4
Conexant
100646A
Conexant Proprietary
1/19/00
Table 1. Swallow Counter Data Input
Synth. Channel No. (A)
Frequency (MHz)
S5
S4
S3
S2
S1
S0
0
2392.2
0
0
0
0
0
0
1
2394.0
0
0
0
0
0
1
2
2395.8
0
0
0
0
1
0
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
6
2403.0
0
0
0
1
1
0
7
2404.8
0
0
0
1
1
1
8
2406.6
0
0
1
0
0
0
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
25
2437.2
0
1
1
0
0
1
26
2439.0
0
1
1
0
1
0
27
2440.8
0
1
1
0
1
1
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
45
2473.2
1
0
1
1
0
1
46
2475.0
1
0
1
1
1
0
47
2476.8
1
0
1
1
1
1
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
61
2502.0
1
1
1
1
0
1
62
2503.8
1
1
1
1
1
0
63
2505.6
1
1
1
1
1
1
2400 MHz Digital Spread Spectrum Transceiver
RF109
100646A
Conexant
5
1/19/00
Conexant Proprietary
Recommendations on Layout and Implementation _______
A typical applications schematic is shown in Figure 5.
Decouple all Vcc pins as close as possible to the supply pin.
All ground pins should have minimum trace inductance to
ground. If a ground plane cannot be provided right at the pins,
the vias to the ground plane should be placed as close to the
pins as possible. There should be one via for each ground pin. If
the ground plane is at the bottom layer, it is recommended to
have two vias in parallel for each ground pin.
Connect all no connect (NC) pins to the ground.
VCC1 (pin 6), VCC2 (pin 7), VCC3 (pin 25), and VCC4 (pin 31)
should be connected to the common Vcc supply through
individual decoupling networks.
R
TXD
should be chosen to provide a typical baseband spread
spectrum signal level of 0.10 Vp-p, to the TXD pin (pin 8).
The routing of the trace to pin 3 (FREF) is very important to
minimize the coupling of the reference clock (9.6 MHz) into the
LO. The FREF trace should be well isolated from all other
traces, preferably by grounded strips on either side of the trace.
All traces from the VCO to pins 38 and 39 should be as short as
possible with a characteristic impedance of 50
.
Exposed Paddle Soldering ____________________________
The RF109 48-pin TQFP package has an exposed (metal)
paddle on the bottom. The footprint dimensions of the exposed
paddle are shown in Figure 6. The printed circuit board should
provide through hole connections to the ground plane to ground
the exposed paddle. The solder mask opening should have the
same size as the exposed paddle. All relevant manufacturing
considerations for this type of package should be taken into
account.
ESD Sensitivity______________________________________
The RF109 is a static-sensitive electronic device. Do not operate
or store near strong electrostatic fields. Take proper
Electrostatic Discharge (ESD) precautions.
CLK
FREF
DATA
1500pF
RXEN
LNAATTN
VBAT
0.047F
8.2pF
STROBE
0.047
F
Cservo
0.082F
Cservo
0.082F
10
VBAT
91
VREG
VCO
BALUN
100
91
VCO SHIELD AREA
12pF
12pF
VCC
GND
TUNE
OUT
GND
NC
RF109
1
2
3
4
5
6
7
8
12
9
10
11
36
35
34
33
32
31
30
29
25
28
27
26
13 14
15 16
17 18
19 20
24
21 22
23
48 47
46 45
44 43
42 41
37
40 39
38
0.01
F
8.2
pF
VCC
GND2
OUT
CTRL
GND1
BYP
VBAT
VREG
10
8.2
pF
1.0pF
402
402
820pF
820pF
470
0.047
F
1.2k
Rmod
2200
pF
12pF
12pF
Rgmc
390pF
0.01F
10k
10k
330pF
TXD
825
82H
3.6k
R
TXD
1.8pF
SYNTHEN
8.2pF
75
OUT
GND
INPUT
OUT
GND
NC
1500pF
3V REGULATOR
0.056F
8.2
pF
1000
pF
8.2
pF
47
F
1000
pF
10
10
PS1
PS2
AGC
RXI+
RXI-
RXQ+
RXQ-
LNAIN
RFO1
RFO2
TXEN
+
-
47
pF
47nF
47nF
8.2pF
8.2pF
8.2pF
0.01F
47nF
8.2pF
8.2pF
8.2pF
8.2pF
8.2pF
Figure 5. Typical Application Diagram RF109
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