Conexant RF109 Datasheet

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 2400–2483.5 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 2392.2–2505.6 MHz.

The RF109 features low-voltage operation (3.0–4.5V) 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.

VCC6

STROBE

NC8

NC1

CLK
FREF
DATA

TXREF

VCC1
VCC2

TXD
RXEN

LNAATTN

LNAIN

NC2

SYNTHEN

48474645444342
1
2
3
4
5
6
7
8
9
10
11
12

13141516171819

RFO1

GND1

GMCRES

Figure 1. RF109 Pin Signals

VCC5

RF109

RFO2

GND2

NC7

CHPO

TXEN

MIXBPC

NC6

VCO2

NC5

4137403938

2024212223

PS2

PS1

MODSET

VCO1

NC4

36
35
34
33
32
31
30
29
28
27
26
25

AGC

GCREF

NC3
SRI+
SRI­SRQ+
SRQ­VCC4
GND3
RXI+
RXI­RXQ+
RXQ­VCC3

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

•

− LNA/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 typ ical)

− 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

Data Sheet Doc. No. 100646A

Conexant Proprietary

January 19, 2000

RF109 2400 MHz Digital Spread Spectrum Transceiver

External

CSERVO

LNAIN

LNAATTN

LNA

RXI

GMCRES

AGC
RXQ

o

90

RFO1
RFO2

MODSET

PS1
PS2

Modulator

Gain

Control

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 Quadrature­phase (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
high-pass cutoff is set by the value of the C
connected between pins 32–33, and pins 34–35.

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

= 820 kHz, R

LPF

= 20 kHz, C

f

HPF

gmc

resistor connected to pin 13. The

servo

capacitors

gmc

servo

Ω

= 825
= 0.082 µF

Synthesizer

External

CSERVO

Interface

Serial

Power
Mgmt.

External

VCO

LPF

FREF

STROBE
CLK
DATA

RXEN
SYNTHEN
TXEN

TXD

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 100Ω differential load. If a single-ended
connection is required, then the unused output must be suitably
terminated by a 50Ω 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

mod

of R

(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.

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.

2

Conexant Proprietary 1/19/00

Conexant

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.

100646A

2400 MHz Digital Spread Spectrum Transceiver RF109

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

= (D) × (FREF/R) × ((M × N) + (A + 1)),

LO

where N > A.

Example:

= 3 × (9.6 MHz / 16) × ((16 × 83) + 7) = 2403.0 MHz

f

LO

= 3 × (9.6 MHz / 16) × ((16 × 83) + 46) = 2473.2 MHz

f

LO

Data Format.

The synthesizer is programmed with a half­duplex 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:

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.

CHPO
pin 43

0.01µF
390
pF

Figure 3. Typical Loop Fi lter

10k

10k

Ω

Ω

VCO

TUNE

330
pF

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.

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.

MSB LSB

DATA

CLK

STROBE

t1 t2 t3

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

1µs each

Figure 4. Timing Diagram

t5

t4

100646A

Conexant

1/19/00 Conexant Proprietary

3

RF109 2400 MHz Digital Spread Spectrum Transceiver

Table 1. Swallow C ounter Data Input

Synth. Channel No. (A) Frequency (MHz) S5 S4 S3 S2 S1 S0

0 2392.2 000000
1 2394.0 000001
2 2395.8 000010

.

.

.

6 2403.0 000110
7 2404.8 000111
8 2406.6 001000

.

.

.

25 2437.2 011001
26 2439.0 011010
27 2440.8 011011

.

.

.

45 2473.2 101101
46 2475.0 101110
47 2476.8 101111

.

.

.

61 2502.0 111101
62 2503.8 111110
63 2505.6 111111

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

.

4

Conexant

100646A

Conexant Proprietary 1/19/00