TRF4900
SINGLE-CHIP RF TRANSMITTER
SLWS092F – JULY 2000 – REVISED JANUARY 2002
D
D
D
D
D
D
D
D
D
D
Single-Chip RF Transmitter for 868-MHz
and 915-MHz ISM Bands
850-MHz to 950-MHz Operation
FM/FSK Operation for Transmit
24-Bit Direct Digital Synthesizer (DDS) With
11-Bit DAC
On-Chip Voltage-Controlled Oscillator
(VCO) and Phase-Locked Loop (PLL)
On-Chip Reference Oscillator
Minimal External Components Required
Low Power Consumption
Typical Output Power of 7 dBm
D
D
D
D
D
Typical Output Frequency Resolution of
230 Hz
Ultrafast Lock Times From DDS
Implementation
Two Fully-Programmable Operational
Modes
2.2-V to 3.6-V Operation
Flexible Serial Interface to TI MSP430
Microcontroller
24-Pin Plastic Thin-Shrink Small-Outline
Package (TSSOP)
PW PACKAGE
(TOP VIEW)
PD_OUT1
PLL_VCC
PD_SET
VCO_TANK1
VCO_TANK2
PLL_GND
DIG_GND
CLOCK
DATA
STROBE
MODE
STDBY
1
2
3
4
5
6
7
8
9
10
11
12
24
23
22
21
20
19
18
17
16
15
14
13
PD_OUT2
LOCKDET
PA_OUT
PA_GND
PA_VCC
GND
DIG_VCC
XOSC2
XOSC1
DIG_GND
TX_DATA
NC
description
The TRF4900 single-chip solution is an integrated circuit intended for use as a low cost FSK transmitter to
establish a frequency-agile RF link. The device is available in a 24-lead TSSOP package and is designed to
provide a fully-functional multichannel transmitter. The chip is intended for linear (FM) or digital (FSK) modulated
applications in the new 868-MHz European band and the North American 915-MHz ISM band. The single chip
transmitter operates down to 2.2 V and is expressly designed for low power consumption. The synthesizer has
a typical channel spacing of approximately 230 Hz to allow narrow-band as well as wide-band applications. Due
to the narrow channel spacing of the direct digital synthesizer (DDS), the DDS can be used to adjust the TX
frequency and allows the use of inexpensive reference crystals.
Two fully-programmable operation modes, Mode0 and Mode1, allow extremely fast switching between two
preprogrammed settings (e.g., TX_frequency_0/TX_frequency_1) without reprogramming the device. Each
functional block of the transmitter can be specifically enabled or disabled via the serial interface.
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
Copyright 2002, Texas Instruments Incorporated
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
POST OFFICE BOX 655303
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1
TRF4900
SINGLE-CHIP RF TRANSMITTER
SLWS092F – JULY 2000 – REVISED JANUARY 2002
ISM band standards
Europe has assigned a new unlicensed frequency band of 868 MHz to 870 MHz. This new band is specifically
defined for short range devices with duty cycles from 0.1% to 100% in several sub-bands. The existing 433-MHz
band for short-range devices in Europe has the great disadvantage of very high usage. The new European
frequency band, due to the duty cycle assignment, allows a reliable RF link and makes many new applications
possible.
The North American unlicensed ISM (industrial, scientific, and medical) band covers 902 MHz to 928 MHz
(center frequency of 915 MHz) and is suitable for short range RF links.
transmitter
The transmitter consists of an integrated VCO, a complete fully-programmable direct digital synthesizer, and
a power amplifier. The internal VCO can be used with an external tank circuit or an external VCO. The divider,
prescaler, and reference oscillator require only the addition of an external crystal and a loop filter to provide a
complete DDS with a typical frequency resolution of 230 Hz.
The 8-bit FSK frequency deviation register determines the frequency deviation in FSK mode. The modulation
itself is done in the direct digital synthesizer, hence no additional external components are necessary.
Since the typical RF output power is approximately 7 dBm, no additional external RF power amplifier is
necessary in most applications.
The TRF4900 RF transmitter is suitable for use in applications that include the TRF6900 RF transceiver.
baseband interface
The TRF4900 can easily be interfaced to a baseband processor such as the Texas Instruments MSP430
ultralow-power microcontroller (see Figure 1). The TRF4900 serial control registers are programmed by the
MSP430, and the MSP430 performs baseband operations in software.
Antenna
Microcontroller
Section
RF Section
TX_DATA
LOCKDET
RF Out
PA_OUT
TRF4900
TRANSMITTER
+
DISCRETES
MODE
STDBY
DATA
CLOCK
STROBE
Transmit Data
Lock Detect
Mode Select
Standby
MSP430
Family µC
Programmable
Digital I/O Pins
Serial Control Data
Serial Control Clock
Serial Control Strobe
Figure 1. System Block Diagram for Interfacing to the MSP430 Microcontroller
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TRF4900
SINGLE-CHIP RF TRANSMITTER
SLWS092F – JULY 2000 – REVISED JANUARY 2002
functional block diagram
PLL_VCC
PD_SET
VCO_TANK1
VCO_TANK2
PLL_GND
DIG_GND
CLOCK
DATA
STROBE
MODE
STDBY
24
1
2
23
PLL
3
4
5
22
21
6
20
TRF4900
7
19
18
8
9
PD_OUT2
LOCKDET
Power
Amplifier
VCO
PD_OUT1
Serial
Interface
10
Direct Digital
Synthesizer,
Power-Down Logic,
and Buffers
11
17
16
15
14
12
13
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• DALLAS, TEXAS 75265
PA_OUT
PA_GND
PA_VCC
GND
DIG_GND
XOSC2
XOSC1
DIG_GND
TX_DATA
NC
3
TRF4900
SINGLE-CHIP RF TRANSMITTER
SLWS092F – JULY 2000 – REVISED JANUARY 2002
Terminal Functions
TERMINAL
NAME
CLOCK
DATA
NO.
I/O
DESCRIPTION
8
I
Serial interface clock signal
9
I
Serial interface data signal
DIG_GND
7, 15
DIG_VCC
18
Digital ground
GND
19
LOCKDET
23
O
PLL lock detect output, active high. PLL locked when LOCKDET = 1.
MODE
11
I
Mode select input. The functionality of the device in Mode0 or Mode1 can be programmed via the A-, B-, C-,
and D-words of the serial control interface.
NC
13
PA_GND
21
PA_OUT
22
PA_VCC
20
PD_OUT1
1
O
Charge pump output – PLL in locked condition
PD_OUT2
24
O
Charge pump output – PLL in unlocked condition
PD_SET
3
Charge pump current setting terminal. An external resistor, RPD, is connected to this terminal to set the
nominal charge pump current.
PLL_GND
6
PLL ground
PLL_VCC
2
STDBY
12
I
Standby control for the TRF4900, active low. While STDBY = 0, the contents of the control registers are still
valid and can be programmed via the serial control interface.
STROBE
10
I
Serial interface strobe signal
TX_DATA
14
I
Digital modulation buffered input for FSK/FM modulation of the carrier, active high
VCO_TANK1
4
I
VCO tank circuit connection. Should be left open if an external VCO is used.
Digital supply voltage
Ground
No connection
Power amplifier ground
O
Power amplifier output, open collector
Power amplifier supply voltage
PLL supply voltage
VCO_TANK2
5
I
VCO tank circuit connection. May also be used to input an external VCO signal.
XOSC1
16
O
Reference crystal oscillator connection
XOSC2
17
I
Reference crystal oscillator connection. May be used as a single-ended clock input if an external crystal
is not used.
4
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TRF4900
SINGLE-CHIP RF TRANSMITTER
SLWS092F – JULY 2000 – REVISED JANUARY 2002
absolute maximum ratings over operating free-air temperature (unless otherwise noted)†
Supply voltage range, PA_VCC, PLL_VCC, DIG_VCC, VCC (see Note 1) . . . . . . . . . . . . . . . . –0.6 to 4.5 Vdc
Input voltage, logic signals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . –0.6 to 4.5 Vdc
Storage temperature range . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . – 65°C to 150°C
ESD integrity‡ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 kV HBM
{ Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratings only, and
functional operation of the device at these or any other conditions beyond those indicated under “recommended operating conditions” is not
implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
‡ RF terminal 22, PA_OUT, is not protected against voltage stress higher than 800 V HBM.
NOTE 1: All GND and VCC terminals must be connected to either ground or supply, respectively, even if the function block is not used.
recommended operating conditions
MIN
TYP
MAX
UNIT
Supply voltage, PA_VCC, PLL_VCC, DIG_VCC, DDS_VCC, VCC
2.2
3.6
V
Operating temperature
–20
60
°C
High-level input voltage, VIH (DATA, CLOCK, STROBE, TX_DATA, MODE, STDBY)
VCC–0.5
V
Low-level input voltage, VIL (DATA, CLOCK, STROBE, TX_DATA, MODE, STDBY)
High-level output voltage, VOH (LOCKDET); IOH = 0.5 mA
0.5
VCC–0.5
V
V
Low-level output voltage, VOL (LOCKDET); IOL = 0.5 mA
0.5
V
electrical characteristics over full range of operating conditions, (typical values are at PA_VCC,
PLL_VCC, DIG_VCC, VCC = 3 V, TA = 25°C) (unless otherwise noted)
supply current consumption in each mode
MODE
ACTIVE STAGES
Power down (standby mode)
MIN
None
TYP
MAX
UNIT
µA
0.5
PA STATE
0 dB attenuation
TX
10 dB attenuation
58
DDS, PLL, VCO, PA
75
mA
27
20 dB attenuation
22
PA disabled
10
12.5
VCO
PARAMETER
TEST CONDITIONS
Frequency range
Phase noise
MIN
TYP
850
50-kHz offset
Tuning voltage
• DALLAS, TEXAS 75265
950
–94
0.5
POST OFFICE BOX 655303
MAX
UNIT
MHz
dBc/Hz
VCC – 0.4
V
5
TRF4900
SINGLE-CHIP RF TRANSMITTER
SLWS092F – JULY 2000 – REVISED JANUARY 2002
electrical characteristics over full range of operating conditions, (typical values are at PA_VCC,
PLL_VCC, DIG_VCC, VCC = 3 V, TA = 25°C) (unless otherwise noted) (continued)
direct digital synthesizer (DDS)
PARAMETER
TEST CONDITIONS
Reference oscillator input frequency,
frequency ƒreff
MIN
TYP
MAX
As oscillator
15
26
As buffer
15
26
0
4194303
Programmable DDS divider ratio
22 bits
DDS divider resolution, ∆ƒ
UNIT
MHz
N × ƒref ÷ 224
FSK – modulation register ratio
8 bits
0
1020
N × ƒref ÷ 222
FSK – modulation resolution
PLL
PARAMETER
TEST CONDITIONS
RF input frequency
MIN
TYP
MAX
UNIT
950
MHz
850
RF input power
Internal VCO bypassed; external input applied to VCO_TANK2
RF input divider ratio, N
–10
dBm
256
512
N × ƒref ÷ 224
RF output frequency resolution
Charge pump current
Programmable with external resistor, 100 kΩ nominal, APLL = 0
µA
70
power amplifier
PARAMETER
TEST CONDITIONS
Frequency range
MIN
TYP
MAX
UNIT
950
MHz
850
Amplifier output power (see Note 2)
0-dB attenuation
7
10-dB attenuation
–3
20-dB attenuation
–12
dBm
Amplifier off
Optimal load impedance
2nd-order harmonic
–52
See Figure 11
VCC = 3 V, 0-dB attenuation
VCC = 3 V, 0-dB attenuation
3rd-order harmonic
Ω
–13
dBc
–32
dBc
NOTE 2: The device and output matching network (see Application Information section) is designed to provide the output power into a 50-Ω load.
The device stability was tested (no parasitic oscillations) with an output VSWR of 10:1 over all phase angles and is not tested in
production.
typical mode switching and lock times
OPERATION
Standby to transmit time†
TEST CONDITIONS
From rising edge of STDBY to valid RF signal at PA_OUT, APLL = 111b
(maximum)
† Highly dependent upon loop filter topology
6
POST OFFICE BOX 655303
• DALLAS, TEXAS 75265
MIN
TYP
500
MAX
UNIT
µs
TRF4900
SINGLE-CHIP RF TRANSMITTER
SLWS092F – JULY 2000 – REVISED JANUARY 2002
timing data for serial interface (see Figure 2)
PARAMETER
MIN
MAX
UNIT
20
MHz
f(CLOCK)
tw(CLKHI)
CLOCK frequency
CLOCK high time pulse width, CLOCK high
25
ns
tw(CLKLO)
tsu(DATA)
CLOCK low time pulse width, CLOCK low
25
ns
Setup time, data valid before CLOCK high
25
ns
th(DATA)
tw(STROBEHI)
Hold time, data valid after CLOCK high
25
ns
Strobe high time pulse width, STROBE high (see Note 3)
25
ns
25
ns
tw(STROBELO)
Strobe low time pulse width, STROBE low
NOTE 3: CLOCK and DATA must both be low when STROBE is asserted (STROBE = 1).
tw(CLKLO)
tw(CLKHI)
tw(STROBEHI)
CLOCK
tsu(DATA)
DATA
tw(STROBELO)
th(DATA)
STROBE
Figure 2. Serial Data Interface Timing
detailed description
reference oscillator
The reference oscillator provides the DDS system clock. It allows operation, with a suitable external crystal,
between 15 MHz and 26 MHz.
An external oscillator can be used to supply clock frequencies between 15 MHz and 26 MHz. The external
oscillator should be directly connected to XOSC2, terminal 17. The other oscillator terminal (XOSC1,
terminal 16) should be left open or can be used as a buffered version of the signal applied at terminal 17 (see
Figure 3). The same crystal or externally supplied oscillator signal is used to derive both the transmit and receive
frequencies.
XOSC1
XOSC2
16
17
NC
External Signal, ƒref
Figure 3. Applying an External Oscillator Signal
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7
TRF4900
SINGLE-CHIP RF TRANSMITTER
SLWS092F – JULY 2000 – REVISED JANUARY 2002
detailed description (continued)
direct digital synthesizer
general principles of DDS operation
In general, a direct digital synthesizer (DDS) is based on the principle of generating a sinewave signal in the
digital domain. Benefits include high precision, wide frequency range, a high degree of software
programmability, and extremely fast lock times.
Figure 4 shows a block diagram of a typical DDS. It generally consists of an accumulator, sine lookup table, a
digital-to-analog converter, and a low-pass filter. All digital blocks are clocked by the reference oscillator.
Synthesizer
+
Sine
Lookup
Table
N-Bit Register
Low-Pass
Filter
DAC
Analog Output Signal
Frequency Register
Load With Frequency Word
Figure 4. Typical DDS Block Diagram
The DDS constructs an analog sine waveform using an N-bit adder counting up from 0 to 2N in steps of the
frequency register whereby generating a digital ramp waveform. Each number in the N-bit output register is used
to select the corresponding sine wave value out of the sine lookup table. After the digital-to-analog conversion,
a low-pass filter is necessary to suppress unwanted spurious responses.
The analog output signal can be used as a reference input signal for a phase-locked loop (PLL). The PLL circuit
multiplies the reference frequency by a predefined factor.
TRF4900 direct digital synthesizer implementation
Figure 5 shows a block diagram of the DDS implemented in the TRF4900. It consists of a 24-bit accumulator
clocked by the reference oscillator along with control logic settings.
24
Reference Frequency, ƒref
+
24-Bit
Register
11
11-Bit
DAC
Sine
Shaper
DDS Frequency Register
MODE – (Terminal 11)
A – Word
DDS Mode0
Frequency Setting
B – Word
DDS Mode1
Frequency Setting
22
D – Word / DEV Bits
(FSK Deviation)
24
22
Mode0/1
Select
Logic
FSK Frequency
Deviation Register
+
8
Modulation
Control
Logic
TX_DATA – (Terminal 14)
C – Word / MM Bit
(Modulation Mode Select)
Figure 5. DDS Block Diagram as Implemented in the TRF4900
8
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• DALLAS, TEXAS 75265
Low-pass
Filter
ƒDDS
to
PLL
TRF4900
SINGLE-CHIP RF TRANSMITTER
SLWS092F – JULY 2000 – REVISED JANUARY 2002
TRF4900 direct digital synthesizer implementation (continued)
The frequency of the reference oscillator, ƒref, is the DDS sample frequency, which also determines the
maximum DDS output frequency. Together with the accumulator width (in bits), the frequency resolution of the
DDS can be calculated. Multiplied by the divider ratio (prescaler) of the PLL, N, the minimum frequency step
size of the TRF4900 is calculated as follows:
ƒ
Dƒ N ref
2 24
+
The 24-bit accumulator can be programmed via two 22-bit frequency setting registers (the A-word determines
the mode0 frequency, the B-word determines the mode1 frequency) with the two MSB bits set to 0.
Consequently, the maximum bit weight of the DDS system is reduced to 1/8 (see Figure 6). This bit weight
corresponds to a VCO output frequency of (ƒref/8) × N. Depending on the MODE terminal’s (terminal 11) logic
level, the internal mode select logic loads the frequency register with either the DDS_0 or DDS_1 frequency
(see Figure 5 and Figure 6).
22
DDS Frequency Setting For Mode0/1
From A-Word/B-Word
... X X X X X
0 0 X X ....
DDS Frequency Register
LSB
MSB
23 22 21 20 . . .
Bit weight: 1/2 1/4 1/8 1/16 . . .
... 4
3
8
FSK Frequency Deviation Register – DEV
0 0 ....
2
1 0
... 1
2 24
.... X X X X X X X X 0 0
DDS Frequency Register
LSB
MSB
23 22 . . . .
....9 8 7 6 5 4 3 2 1 0
Figure 6. Implementation of the DDS Frequency and FSK Frequency
Deviation in the DDS Frequency Register
The VCO output frequency, ƒout, which is dependent on the DDS_x frequency settings (DDS_0 in the A-word
or DDS_1 in the B-word), can be calculated as follows:
ƒ out
+ DDS_x
ƒ ref
N
2 24
+N
ƒ ref
DDS_x
2 24
If FSK modulation is selected (MM=0; C-Word, bit 16), then the 8-bit FSK deviation register can be used to
program the frequency deviation of the 2-FSK modulation. Figure 6 illustrates where the 8 bits of the FSK
deviation register map into the 24-bit DDS frequency register. Since the two LSBs are set to 0, the total FSK
deviation can be determined as follows:
Dƒ2–FSK + N
ƒ ref
DEV
2 22
Hence, the 2-FSK frequency, set by the level on the TX_DATA is calculated as follows:
ƒ out1:TX_DATA+Low
+N
ƒ ref
DDS_x
2 24
ƒ out2:TX_DATA+High
+N
ƒ ref
(DDS_x
)4
DEV)
2 24
This frequency modulated output signal is used as a reference input signal for the PLL circuit. Channel width
(frequency deviation) for 2-FSK modulation and channel spacing are software programmable. The minimum
channel width and minimum channel spacing depend on the RF system frequency plan.
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TRF4900
SINGLE-CHIP RF TRANSMITTER
SLWS092F – JULY 2000 – REVISED JANUARY 2002
TRF4900 direct digital synthesizer implementation (continued)
Note that the frequencies ƒout1 and ƒout2 are centered about the frequency ƒcenter = (ƒout1 + ƒout2)/2. When
transmitting FSK, ƒcenter is considered to be the effective carrier frequency and any receiver local oscillator (LO)
should be set to the same ƒcenter frequency ± the receiver’s IF frequency (ƒIF) for proper reception and
demodulation.
For the case of low-side injection, the receiver LO would be set to ƒLO = ƒcenter – ƒIF. Conversely, for high-side
injection, the receiver LO would be set to ƒLO = ƒcenter + ƒIF.
Since the DDS registers are static, preprogrammed values are retained during standby mode. This feature
greatly reduces turnon time, reduces current consumption when coming out of standby mode, and enables very
fast lock-times. The PLL lock-times ultimately determine when data can be transmitted or received.
phase-locked loop
The phase-locked loop (PLL) of the TRF4900 consists of a phase detector (PD) and a frequency acquisiton aid
(FD) (including two charge pumps), an external loop filter, voltage-controlled oscillator (VCO), and a
programmable fixed prescaler (N-divider) in the feedback loop (see Figure 7).
The PLL as implemented in the TRF4900 multiplies the DDS output frequency and further suppresses the
unwanted spurious signals produced by the direct digital synthesizer.
DDS
ƒDDS
PD
1
IPD_1
IPD_2
ƒref
FD
External
Loop Filter
4, 5
VCO
ƒout
24
N-Divider
256 / 512
Figure 7. Basic PLL Structure
VCO
A modified Colpitts oscillator architecture with an external resonant circuit is used for the TRF4900. The internal
bias current network adjusts the signal amplitude of the VCO. This allows a wide range of Q-factors (30…60)
for the external tank circuit.
The VCO can be bypassed by applying an external RF signal at VCO_TANK2, terminal 5. To drive the internal
PLL and power amplifier, a typical level of –10 dBm should be applied. When an external VCO is used, the
x_VCO bit should be set to 0.
phase detector and charge pumps
The TRF4900 contains two charge pumps for locking to the desired frequency: one for coarse tuning of the
frequency differences (called the frequency acquisition aid), and one for fine tuning of the phase differences
(used in conjunction with the phase detector).
The XOR phase detector and charge pumps produce a mean output current that is proportional to the phase
difference between the reference frequency and the VCO frequency divided by N; N = 256 or 512. The TRF4900
generates the current pulses IPD_1 during normal operation (PLL locked).
An additional slip detector and acquisition aid charge pump generates current pulses at terminal PD_OUT2
during the lock-in of the PLL. This charge pump is turned off when the PLL locks in order to reduce current
consumption. The multiplication factor of the acquisition aid current IPD_2 can be programmed by three bits
(APLL) in the C-word.
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TRF4900
SINGLE-CHIP RF TRANSMITTER
SLWS092F – JULY 2000 – REVISED JANUARY 2002
phase detector and charge pumps (continued)
The slip detector output, PD_OUT2, at terminal 24 should be connected directly to the loop filter capacitor C1,
as shown in Figure 10. The nominal charge pump current I0 is determined by the external resistor RPD,
connected to terminal 3, and can be calculated as follows:
I0
+ R7 PDV
During normal operation (PLL locked), the acquisition aid charge pump is disabled and the maximum charge
pump current IPD_1 is determined by the nominal value I0 (see Figure 8).
I0
IPD_1
1
Figure 8. Normal Operation Charge Pump Current, IPD_1
Each time the PLL is in an unlocked condition, the acquisition aid charge pump generates current pulses IPD_2.
The IPD_2 current pulses are APLL times larger than I0 (see Figure 9).
1
IPD_1
APLL
IPD_2
I0
Figure 9. Acquisition Aid, IPD_2, and Normal Operation, IPD_1, Charge Pump Currents
programmable divider
The internal divider ratio, N, can be set to 256 or 512 via the C-word. Since a higher divider ratio adds additional
noise within the multiplication loop, the lowest divider ratio possible for the target application should be used.
loop filter
Loop filter designs are a balance between lock-time, noise, and spurious suppression. For the TRF4900,
common loop filter design rules can be used to determine an appropriate low-pass filter. Standard formulas can
be used as a first approach to calculate a basic loop filter. Figure 10 illustrates a basic 3rd-order loop filter.
VCO_TANK1
C3
VCO_TANK2
5
4
R2
1
PD_OUT1
C3c
L1
R1
PD_OUT2
24
C3d
C2
VCO
C4
C1
2nd-Order Loop Filter
3rd-Order Loop Filter
Figure 10. Basic 3rd-Order Loop Filter Structure
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11
TRF4900
SINGLE-CHIP RF TRANSMITTER
SLWS092F – JULY 2000 – REVISED JANUARY 2002
loop filter (continued)
For maximum suppression of the unwanted frequency components, the loop filter bandwidth should generally
be made as narrow as possible. At the same time, the filter bandwidth has to be wide enough to allow for the
2-FSK modulation and appropriate lock-time. A detailed simulation of the phase-locked loop should be
performed and later verified on PCB implementations.
power amplifier
The power amplifier (PA) can be programmed via two bits (P0 and P1 in the D-word) to provide varying output
power levels. Several control loops are implemented internally to set the output power and to minimize the
sensitivity of the power amplifier to temperature, load impedance, and power supply variations. The output stage
of the PA usually operates in Class-C and enables easy impedance matching. PA_OUT, terminal 22, is an open
collector output terminal.
↑1 U
CH1 S22
1
2
0.5
5
CAL
OFS
0
0.2
0.5
1
2
10
CPL
–5
1
FIL
1k
–2
–0.5
–1
START 850 MHz
STOP 950 MHz
Figure 11. Power Amplifier Output Impedance (S22) at Device Terminal 22
12
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TRF4900
SINGLE-CHIP RF TRANSMITTER
SLWS092F – JULY 2000 – REVISED JANUARY 2002
PRINCIPLES OF OPERATION
serial control interface
A 3-wire unidirectional serial bus (CLOCK, DATA, STROBE) is used to program the TRF4900 (see Figure 12).
The internal registers contain all user programmable variables including the DDS frequency setting registers,
as well as all control registers.
At each rising edge of the CLOCK signal, the logic value on the DATA terminal is written into a 24-bit shift register.
Setting the STROBE terminal high loads the programmed information into the selected latch. While the
STROBE signal is high, the DATA and CLOCK lines must be low (see Figure 2). Since the CLOCK and STROBE
signals are asynchronous, care should be taken to ensure the signals remain free of glitches and noise.
As additional leading bits are ignored, only the least significant 24 bits are serial-clocked into the shift register.
Due to the static CMOS design, the serial interface consumes virtually no current and it can be programmed
in active as well as in standby mode.
CLOCK
STROBE
Serial Interface
Logic
Shift Register
DATA
22
A - Latch
22
ADDR
3
B - Latch
ADDR
Decoder
21
C - Latch
21
D - Latch
21
E - Latch
Figure 12. Serial Interface Block Diagram
The control words are 24 bits in length. The first incoming bit functions as the most significant bit (MSB).
To fully program the TRF4900, four 24-bit words must be sent: the A-, B-, C-, and D-words. If individual bits within
a word are to be changed, then it is sufficient to program only the appropriate 24-bit word.
Figure 13 shows the definition of the control words. Tables 1, 2, and 3 describe the function of each parameter.
The E-Latch, addressed by an ADDR equal to 111, is reserved for test purposes and should not be used.
Inadvertently addressing the E-Latch activates the test modes of the TRF4900.
If the test mode has been inadvertently activated, it can only be exited by switching VCC on and off or by clearing
the E-Latch. The E-Latch can be cleared by addressing it and resetting its entire contents by programming
1110 0000 0000 0000 0000 0000.
As part of a proper power-up sequence, it is recommended to clear the E-Latch each time VCC is applied before
starting further operations with the TRF4900.
POST OFFICE BOX 655303
• DALLAS, TEXAS 75265
13
TRF4900
SINGLE-CHIP RF TRANSMITTER
SLWS092F – JULY 2000 – REVISED JANUARY 2002
PRINCIPLES OF OPERATION
A-Word (Programming of DDS_0)
MSB
23
0
22 21
20
19 18 17
0
LSB
16 15
14 13
12 11
10
9
8
7
6
5
4
3
2
1
0
DDS Frequency Setting for Mode0 (DDS_0 [21–0])
ADDR
B-Word (Programming of DDS_1)
MSB
23
0
22 21
20
19 18 17
LSB
16 15
14 13
12 11
10
9
8
7
6
5
4
3
2
1
0
DDS Frequency Setting for Mode1 (DDS_1 [21–0])
1
ADDR
C-Word (Control Register for PLL, Data Slicer, and Mode1 Settings)
MSB
23
22 21
20
19 18 17
16 15
14 13
12 11
10
9
LSB
8
7
6
5
4
3
2
1
0
X
X
X
X
X
X
X
X
Mode1 Control Register [12–9]
1
0
PLL
1
APLL
A2
ADDR
A1
X
X
X X
PA
PLL VCO
NPLL MM
P1
A0
P0
D-Word (Control Register for Modulation and Mode0 Settings)
MSB
23
22 21
20
19 18 17
16 15
14 13
12 11
LSB
10
9
8
7
6
5
4
3
2
1
0
X
X
X
X
X
X
X
X
Mode0 Control Register [12–9]
1
1
0
DEV
ADDR
X
Modulation Register [20–13]
PA
PLL VCO
DV7 DV6 DV5 DV4 DV3 DV2 DV1 DV0
P1
P0
NOTE: Start programming with MSB and ensure that the CLOCK and DATA lines are low during the rising edge of the strobe signal.
Figure 13. Serial Control Word Format
14
POST OFFICE BOX 655303
• DALLAS, TEXAS 75265
TRF4900
SINGLE-CHIP RF TRANSMITTER
SLWS092F – JULY 2000 – REVISED JANUARY 2002
PRINCIPLES OF OPERATION
Table 1. Mode0 Control Register Description (D-Word)
SYMBOL
0_PA
BIT
LOCATION
NUMBER
OF BITS
[10–9]
Power amplifier mode
P1
0
0
1
1
2
0_VCO
[11]
0_PLL
[12]
DESCRIPTION
INITIAL SETTINGS
AFTER POWER UP
DEFAULT
STATE
DEFAULT
VALUE
Disabled
00b
P0
0 = disabled
1 = 10 dB attenuation, enable modulation via TX_DATA
0 = 20 dB attenuation, enable modulation via TX_DATA
1 = 0 dB attenuation, enable modulation via TX_DATA
1
During operation, this bit should always be enabled (1 = enabled), unless
an external VCO is used.
Disabled
0b
Enable PLL (DDS system, VCO, RF divider, phase comparator and charge
pump)
1 = enabled
0 = disabled
Disabled
0b
1
Table 2. Mode1 Control Register Description (C-Word)
SYMBOL
1_PA
BIT
LOCATION
NUMBER
OF BITS
[10–9]
Power amplifier mode
2
1_VCO
[11]
1_PLL
[12]
DESCRIPTION
P1
0
0
1
1
INITIAL SETTINGS
AFTER POWER UP
DEFAULT
STATE
DEFAULT
VALUE
Disabled
00b
P0
0 = disabled
1 = 10 dB attenuation, enable modulation via TX_DATA
0 = 20 dB attenuation, enable modulation via TX_DATA
1 = 0 dB attenuation, enable modulation via TX_DATA
1
During operation, this bit should always be enabled (1 = enabled), unless
an external VCO is used.
Disabled
0b
Enable PLL (DDS system, VCO, RF divider, phase comparator and charge
pump)
1 = enabled
0 = disabled
Disabled
0b
1
POST OFFICE BOX 655303
• DALLAS, TEXAS 75265
15
TRF4900
SINGLE-CHIP RF TRANSMITTER
SLWS092F – JULY 2000 – REVISED JANUARY 2002
PRINCIPLES OF OPERATION
Table 3. Miscellaneous Control Register Description
SYMBOL
WORD
BIT
LOCATION
NUMBER
OF BITS
DDS_0
A-word
[21–0]
22
DDS_1
B-word
[21–0]
DEV
D-word
[20–13]
APLL
C-word
[20–18]
DESCRIPTION
INITIAL SETTINGS
AFTER POWER UP
DEFAULT
STATE
DEFAULT
VALUE
DDS frequency setting in Mode0
0
All 0s
22
DDS frequency setting in Mode1
0
All 0s
8
FSK frequency deviation register
0
All 0s
3
Acceleration factor for the frequency acquisition aid charge pump
A2
A1
A0
0
0
0
=1
0
0
1
= 20
0
1
0
= 40
0
1
1
= 60
0
000b
256
0b
FSK
mode
0b
L
1
1
1
= 140
NPLL
C-word
[17]
1
PLL divider ratio
0 = divide by 256
1 = divide by 512
MM
C-word
[16]
1
Modulation mode select. Sets the behavior of terminal TX_DATA
to FSK data input.
0 = FSK/FM
1 = do not use
operating modes
Tables 4 and 5 illustrate operating modes and transmit frequencies as set by the STDBY, MODE, and TX_DATA
terminals used in conjunction with the DDS frequency settings.
Table 4. Transmitting Data in FSK Mode (MM bit set to 0)
TERMINAL
16
TRANSMIT FREQUENCY
STDBY
MODE
TX_DATA
1
0
0
ƒout = ƒref × N × (DDS_0)/224
1
0
1
1
1
0
ƒout = ƒref × N × (DDS_0 + 4 × DEV)/224
ƒout = ƒref × N × (DDS_1)/224
1
1
1
ƒout = ƒref × N × (DDS_1 + 4 × dev)/224
POST OFFICE BOX 655303
• DALLAS, TEXAS 75265
TRF4900
SINGLE-CHIP RF TRANSMITTER
SLWS092F – JULY 2000 – REVISED JANUARY 2002
PRINCIPLES OF OPERATION
operating modes (continued)
Table 5. Operating Mode Per STDBY Terminal
STDBY
OPERATING MODE
0
Standby/programming mode – Power down of all blocks
1
Operating mode and programming mode
Two independent operating modes, Mode0 and Mode1, allow extremely fast switching between two
preprogrammed settings by toggling the MODE terminal. Each mode can be viewed as a bank of configuration
registers which store the frequency settings and the enable/disable settings for each functional block of the
TRF4900. The MODE terminal is then used to asynchronously switch between Mode0 and Mode1 as shown
in Figure 14. Table 6 shows several examples of operating sequences.
MODE Terminal (Terminal 11) = 1
Mode0 Register Settings
(D-Word)
Mode1 Register Settings
(C-Word)
Power Amplifier Mode
Power Amplifier Mode
VCO Enable
VCO Enable
PLL Enable
PLL Enable
Synthesizer:
DDS Frequency
Synthesizer:
DDS Frequency
MODE Terminal (Terminal 11) = 0
Figure 14. Interaction Between MODE Terminal and Preprogrammed Mode0 and Mode1 Control Registers
Table 6. Operating Mode Examples
FUNCTION/DESCRIPTION
MODE0
MODE1
Transmit on two different frequencies
Transmit on frequency 0
Transmit on frequency 1
Emulate FSK transmit operation using the MODE terminal for
wideband FSK
Transmit on frequency 0
Transmit on frequency 0 + deviation
POST OFFICE BOX 655303
• DALLAS, TEXAS 75265
17
TRF4900
SINGLE-CHIP RF TRANSMITTER
SLWS092F – JULY 2000 – REVISED JANUARY 2002
APPLICATION INFORMATION
A typical application schematic for an FSK system operating in the European 868-MHz to 870-MHz ISM band is
shown in Figure 15. If the TRF4900 is left on for long periods of time without going into standby mode, a 100-Ω resistor
to ground should be added at terminal 4 or terminal 5 to reduce tuning voltage drift as in Figure 16. If the 100-Ω resistor
is present, C2 and C4 may be changed to adjust the tuning range as needed. Since most EU applications involve
relatively short periods of transmission, the 100-Ω resistor is left off in the schematic shown in Figure 15.
R4
8.2 kΩ
C1
8.2 nF
R1
10 kΩ
C32
820 pF
24
1
2
R3
C2
150 pF
3
68 kΩ
5.6 pF
10 nH
V1
C4
SMV1233–011
2.7 pF
Power
Amplifier
4
5
VCO
C17
LOCKDET
23
PLL
22
21
L8
6
R2
51 Ω
20
TRF4900
7
DATA
C3
8
9
STROBE
10
MODE
11
STDBY
12
Serial
Interface
Direct Digital
Synthesizer and
Power-Down Logic
150 pF
17
C5
150 pF
J1
RF_OUT
SMA/B/L
16
15
TX_DATA
14
13
NC
R5
820 Ω
CQ1
18 MHz
R6
1 MΩ
C24
15 pF
C25
15 pF
Figure 15. Typical Application Schematic for 868-MHz to 870-MHz European ISM Band
18
C14
3.3 pF
19
18
CLOCK
L1
5.6 nH
POST OFFICE BOX 655303
• DALLAS, TEXAS 75265
TRF4900
SINGLE-CHIP RF TRANSMITTER
SLWS092F – JULY 2000 – REVISED JANUARY 2002
APPLICATION INFORMATION
external component list for Figure 15 (5% tolerance unless otherwise noted)
DESIGNATOR
DESCRIPTION (SIZE)
VALUE
MANUFACTURER
C1
Capacitor
8.2 pF
C2
Capacitor
5.6 pF
C3
Capacitor
150 pF
C4
Capacitor
2.7 pF
C5
Capacitor
150 pF
C14
Capacitor
3.3 pF
C17
Capacitor
150 pF
C24
Capacitor
15 pF
C25
Capacitor
15 pF
C32
Capacitor
820 pF
L1
Coil
5.6 nH
Murata
LQN21A6N8D04
L8
Coil
10 nH
Murata
LQW1608
R1
Resistor
10 kΩ
R2
Resistor
51 Ω
R3
Resistor
68 kΩ
R4
Resistor
8.2 kΩ
R5
Resistor
820 Ω
R6
Resistor
1 MΩ
V1
Varactor diode
SMV1233-011
Alpha Industries
CQ1
Crystal
18 MHz
CMAC Frequency Products
POST OFFICE BOX 655303
• DALLAS, TEXAS 75265
PART NUMBER/COMMENTS
CX-1 SMI
19
TRF4900
SINGLE-CHIP RF TRANSMITTER
SLWS092F – JULY 2000 – REVISED JANUARY 2002
APPLICATION INFORMATION
A typical application schematic for an FSK system operating in the North American 902-MHz to 928-MHz ISM band
as shown in Figure 16.
R4
27 kΩ
C1
820 pF
C32
120 pF
24
1
2
R3
R1
10 kΩ
R7
V1 10 kΩ
SMV1247–079
C2
3.9 pF
10 nH
L8
C4
3.9 pF
V2
SMV1247–079
3
300 kΩ
Power
Amplifier
4
5
22
20
TRF4900
L1
6.8 nH
19
7
R9
18
CLOCK
8
DATA
9
STROBE
10
MODE
11
STDBY
12
Serial
Interface
Direct Digital
Synthesizer and
Power-Down Logic
C14
3.3 pF
R2
51 Ω
21
6
R8
100 kΩ
LOCKDET
23
PLL
VCO
C6
0.1 µF
C34
0.1 µF
17
C5
0.1 µF
15 Ω
J1
RF_OUT
SMA/B/L
16
15
14
13
R5
100 Ω
TX_DATA
NC
CQ1
25.6 MHz
or 26 MHz
1M
R6
C24
27 pF
C25
27 pF
C26
SAT
DNP
Figure 16. Typical Application Schematic for 902-MHz to 928-MHz North American ISM Band
20
POST OFFICE BOX 655303
• DALLAS, TEXAS 75265
TRF4900
SINGLE-CHIP RF TRANSMITTER
SLWS092F – JULY 2000 – REVISED JANUARY 2002
APPLICATION INFORMATION
external component list for Figure 16 (5% tolerance unless otherwise noted)
DESIGNATOR
DESCRIPTION (SIZE)
VALUE
MANUFACTURER
PART NUMBER/COMMENTS
C1
Capacitor
820 pF
C2
Capacitor
3.9 pF
C4
Capacitor
3.9 pF
C5
Capacitor
0.1 µF
C6
Capacitor
0.1 µF
C14
Capacitor
3.3 pF
C24
Capacitor
27 pF
C25
Capacitor
27 pF
C26
Capacitor
C32
Capacitor
C34
Capacitor
0.1 µF
L1
Coil
6.8 nH
Murata
LQN21A6N8D04
L8
Coil
10 nH
Murata
LQW1608
R1
Resistor
10 kΩ
R2
Resistor
51 Ω
R3
Resistor
300 kΩ
R4
Resistor
27 kΩ
R5
Resistor
100 Ω
R6
Resistor
1 MΩ
R7
Resistor
10 kΩ
R8
Resistor
100 kΩ
Select at test (SAT), Do not place (DNP)
120 pF
R9
Resistor
15 Ω
V1, V2
Varactor diode
SMV1247-079
Alpha Industries
CQ1
Crystal
25.6 MHz or
26 MHz
ICM (International Crystal
Manufacturing, Incorporated)
POST OFFICE BOX 655303
• DALLAS, TEXAS 75265
865842: 25.6 MHz
865850: 26 MHz
21
TRF4900
SINGLE-CHIP RF TRANSMITTER
SLWS092F – JULY 2000 – REVISED JANUARY 2002
MECHANICAL DATA
PW (R-PDSO-G**)
PLASTIC SMALL-OUTLINE PACKAGE
14 PINS SHOWN
0,30
0,19
0,65
14
0,10 M
8
0,15 NOM
4,50
4,30
6,60
6,20
Gage Plane
0,25
1
7
0°– 8°
A
0,75
0,50
Seating Plane
0,15
0,05
1,20 MAX
PINS **
0,10
8
14
16
20
24
28
A MAX
3,10
5,10
5,10
6,60
7,90
9,80
A MIN
2,90
4,90
4,90
6,40
7,70
9,60
DIM
4040064/F 01/97
NOTES: A.
B.
C.
D.
22
All linear dimensions are in millimeters.
This drawing is subject to change without notice.
Body dimensions do not include mold flash or protrusion not to exceed 0,15.
Falls within JEDEC MO-153
POST OFFICE BOX 655303
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