U3741BM Datasheet, PDF (8/25 Pages) ATMEL Corporation – UHF ASK RECEIVER IC

U3741BM
Pin MODE can now be set in accordance with the desired
clock cycle T_Clk. T_Clk controls the following application-
relevant parameters:
D Timing of the polling circuit including bitcheck
D Timing of the analog and digital signal processing
D Timing of the register programming
D Frequency of the reset marker
D IF filter center frequency (f_IF0)
Most applications are dominated by two transmission
frequencies: f_Send = 315 MHz is mainly used in USA,
f_Send = 433.92 MHz in Europe. In order to ease the usage
of all T_Clk-dependent parameters on this electrical
characteristics display three conditions for each parame-
ter.
D Application USA
(f_XTO = 4.90625 MHz, MODE = L, T_Clk = 2.0383 µs)
D Application Europe
(f_XTO = 6.76438 MHz, MODE = H, T_Clk = 2.0697 µs)
D Other applications
(T_Clk is dependent on f_XTO and on the logical state of
Pin MODE. The electrical characteristic is given as a
function of T_Clk).
The clock cycle of some function blocks depends on the
selected baud rate range (BR_Range) which is defined in
the OPMODE register. This clock cycle T_XClk is defined
by the following formulas for further reference:
BR_Range = BR_Range0: T_XClk = 8 × T_Clk
BR_Range1: T_XClk = 4 × T_Clk
BR_Range2: T_XClk = 2 × T_Clk
BR_Range3: T_XClk = 1 × T_Clk
Polling Mode
According to figure 5 the receiver stays in polling mode
in a continuous cycle of three different modes. In sleep
mode the signal processing circuitry is disabled for the
time period T_Sleep while consuming low current of
I_S = I_Soff. During the start-up period, T_Startup, all signal
processing circuits are enabled and settled. In the
following bitcheck mode, the incoming data stream is
analyzed bit by bit contra a valid transmitter signal. If no
valid signal is present, the receiver is set back to sleep
mode after the period T_Bitcheck. This period varies check
by check as it is a statistical process. An average value for
T_Bitcheck is given in the electrical characteristics. During
T_Startup and T_Bitcheck the current consumption is I_S = I_Son.
The average current consumption in polling mode is
dependent on the duty cycle of the active mode and can
be calculated as:
+ I_Spoll
I_Soff
) ) T_Sleep
) ) T_Sleep
I_Son (T_Startup T_Bitcheck)
T _Startup
T _Bitcheck
During T_Sleep and T_Startup the receiver is not sensitive to
a transmitter signal. To guarantee the reception of a
transmitted command the transmitter must start the
telegram with an adequate preburst. The required length
of the preburst is dependent on the polling parameters
T_Sleep, T_Startup, T_Bitcheck and the startup time of a
connected µC (T_Start,µC). T_Bitcheck thus depends on the
actual bitrate and the number of bits (N_Bitcheck) to be
tested.
The following formula indicates how to calculate the
preburst length.
w T_Preburst T_Sleep + T_Startup + T_Bitcheck + T_{Start_mC}
Sleep Mode
The length of period T_Sleep is defined by the 5-bit word
Sleep of the OPMODE register, the extension factor
XSleep, according to table 10, and the basic clock cycle
T_Clk. It is calculated to be:
T_Sleep = Sleep X_Sleep 1024 T_Clk
In US- and European applications, the maximum value of
T_Sleep is about 60 ms if XSleep is set to 1. The time
resolution is about 2 ms in that case. The sleep time can
be extended to almost half a second by setting XSleep
to 8. XSleep can be set to 8 by bit XSleep_Std or by bit
XSleep_Temp resulting in a different mode of action as
described below:
XSleep_Std = 1 implies the standard extension factor.
The sleep time is always extended.
XSleep_Temp = 1 implies the temporary extension factor.
The extended sleep time is used as long as every bitcheck
is OK. If the bitcheck fails once, this bit is set back to 0
automatically resulting in a regular sleep time. This
functionality can be used to save current in presence of a
modulated disturber similar to an expected transmitter
signal. The connected µC is activated rarely in that
condition. If the disturber disappears, the receiver
switches back to regular polling and is again sensitive to
appropriate transmitter signals.
According to table 7, the highest register value of Sleep
sets the receiver into a permanent sleep condition. The
receiver remains in that condition until another value for
Sleep is programmed into the OPMODE register. This
function is desirable where several devices share a single
data line.
8 (25)
Rev. A1, 15-Oct-98
Preliminary Information