DS2 is a “dB-below-peak” slicer. The peak detector charges rapidly to the
peak value of each data pulse, and decays slowly in between data pulses
(1:1000 ratio). The slicer trip point can be set from 0 to 120 mV below this
peak value with a resistor between RREF and THLD2.
DS2 is best for ASK modulation where the transmitted waveform has been
shaped to minimize signal bandwidth. However, DS2 is subject to being
temporarily “blinded” by strong noise pulses, which can cause burst data
errors. Note that DS1 is active when DS2 is used, as the compound data
slicer output is the logical AND of the DS1 and DS2 outputs. DS2 can be
disabled by leaving THLD2 disconnected. Note that a non-zero DS1
threshold is required for proper AGC operation.
Data and Clock Recovery
RXDATA is the receiver data output pin. The signal on this pin can come
from one of two sources. The default source is directly from the output of
the compound data slicer circuit. The alternate source is from the radio’s
internal data and clock recovery circuit. When the internal data and clock
recovery circuit is used (CFG0 Bit 0 high), the signal on RXDATA is
switched from the output of the data slicer to the output of the data and
clock recovery circuit when a packet start symbol is detected.
When the radio’s internal data and clock recovery circuit is not used, RXD-
CLK is a steady low value. When the internal data and clock recovery is
used, RXDCLK is low until a start symbol is detected at the output of the
data slicer. Each bit following the start symbol is output at RXDATA on the
rising edge of a RXDCLK pulse, and is stable for reading on the falling
edge of the RXDCLK pulse. Once RXDCLK is activated by the detection
of a start symbol, it remains active until CFG0 Bit 0 is reset low. Normally
RXDCLK is reset by the host processor as soon as a packet is received.
AGC Control
The output of the Peak Detector also provides an AGC Reset signal to the
AGC Control function through the AGC comparator. The purpose of the
AGC function is to extend the dynamic range of the receiver, so that two
transceivers can operate close together when running ASK and/or high
data rate modulation. The onset of saturation in the output stage of RFA1
is detected and generates the AGC Set signal to the AGC Control func-
tion. The AGC Control function then selects the 5 dB gain mode for RFA1.
The AGC Comparator will send a reset signal when the Peak Detector
output (multiplied by 0.8) falls below the threshold voltage for DS1.
Digital Modulation (DSSS) Transmitter Chain
The transmitter chain consists of a SAW delay line oscillator, followed by a
double-balanced mixer that applies a “digital modulation” DSSS spreading
code, followed by an OOK/ASK modulated buffer amplifier. The SAW filter
suppresses transmitter harmonics to the antenna. Note that the same
SAW devices used in the amplifier-sequenced receiver are reused in the
transmit modes.
Transmitter operation supports two modulation formats, on-off keyed
(OOK) modulation, and amplitude-shift keyed (ASK) modulation. When
OOK modulation is chosen, the transmitter output turns completely off
between “1” data pulses. When ASK modulation is chosen, a “1” pulse is
represented by a higher transmitted power level, and a “0” is represented
by a lower transmitted power level. OOK modulation provides compatibility
with first-generation ASH technology, and provides for power conserva-
tion. ASK modulation must be used for high data rates (data pulses less
than 30 µs). ASK modulation also reduces the effects of some types of
interference and allows the transmitted pulses to be shaped to control
modulation bandwidth.
When either modulation format is chosen, the receiver RF amplifiers are
turned off. In the OOK mode, the delay line oscillator amplifier TXA1 and
the buffer amplifier TXA2 are turned off when the voltage to the TXMOD
input falls below 220 mV. In the OOK mode, the data rate is limited by the
turn-on and turn-off times of the delay line oscillator, which are 12 and 6 µs
respectively. In the ASK mode TXA1 is biased ON continuously, and the
output of TXA2 is modulated by the TXMOD input current. Minimum out-
put power occurs in the ASK mode when the modulation driver sinks
about 10 µA of current from the TXMOD pin.
The transmitter RF output power is proportional to the input current to the
TXMOD pin. A series resistor is used to adjust the peak transmitter output
power. 10 dBm of output power requires about 315 µA of input current.
Configuration Control
The operating configuration of the TR8100 is controlled by three
pins: Pin 17 (CFGDAT), Pin 18 (CFGCLK), and Pin 19 (CFG).
When DC power is applied to the TR8100 with Pin 19 held low, the
functions of Pins 17 and 18 default to the “2G ASH” TR1000 defini-tion.
This allows the TR8100 to be used with existing TR1000 PCB
layouts and protocol software. The logic levels on Pins 17 and 18
control the default 2G operation as shown below:
Pin 17
1
0
0
1
Pin 18
1
0
1
0
Mode
Receive
Sleep
Transmit OOK
Transmit ASK
NOTE: It is not possible to comply with FCC 15.247 regulations using the
default 2G control mode. In this case, the TR8100 power must be adjusted
to comply with FCC 15.249 regulations. Note that for default 2G operation,
Pin 15 is grounded (zero ohm resistor) and Pin 14 is left unconnected.
When Pin 19 is first set to a logic 1 after DC power is applied, the function-
ality of Pins 17 and 18 change from the 2G control mode to the 3G serial
control mode. This change persists until a power reset.
After serial control is invoked, Pins 17, 18 and 19 are used to write data to
and read from three 8-bit configuration control registers in the radio. To
begin a write or read sequence, Pin 19 is set to logic 1. Data is then
clocked into or out of Pin 17 on the rising edge of each clock pulse applied
to Pin 18. Configuration data clocked into Pin 17 is transferred to a control
register every eight bits. Bits clocked into Pin 17 when Pin 19 is a logic 0
are ignored. Also, if Pin 19 is reset to logic 0 before a complete group of
eight data bits is received, the in-complete group is ignored.
Single-byte and multi-byte write and read sequences are detailed in
Figures 4 and 5. The bits in the configuration registers are summa-rized
in Figure 3.
It is necessary to change the power-on default val-ues
of several bits in CFG0 and CFG1 before the TR8100 will comply with
15.247 regulations. The advantage of the FCC 15.247 “digital modulation”
rules is that the TR8100 can transmit its full rated RF power.
RF Monolithics, Inc.
Phone: (972) 233-2903
Fax: (972) 387-8148
RFM Europe
Phone: 44 1963 251383
Fax: 44 1963 251510
©1999 by RF Monolithics, Inc. The stylized RFM logo are registered trademarks of RF Monolithics, Inc.
E-mail: info@rfm.com
http://www.rfm.com
TR8100-021307
Page 6 of 14
RFM [ RF MONOLITHICS, INC ]
