1996 Oct 31
13
Philips Semiconductors
Objective specification
DECT burst mode controller
PCD5043
6.5.7
L
OCAL CALL SWITCHING
(see Fig.8)
The PCD5043 provides a local call switching function in
the base station. It will store incoming speech nibbles in
the common data memory, in the area reserved for that
particular receive slot. Then, during the transmit phase, it
passes the start pointer of the same data memory area to
the transmit block. Thus, the speech data is echoed to the
other user. To handle quality degradation for local calls, a
mute can be performed at the RF side of the speech buffer.
6.5.8
D
ATA SYNCHRONIZATION
(see Fig.9)
The data synchronization is done in 2 phases:
Bit synchronization
Sync word detection.
Bit synchronization is done using a Digital PLL (DPLL),
with an oversampling factor of 12, i.e. the DPLL is running
at 12 times the data rate. The output from the DPLL is a
receive clock signal (RxC), which acts as the enable for a
20-bit shift register.
Sync word detection is achieved by checking the incoming
data pattern with the expected synchronization field
pattern, using a correlator.
The correlator has a programmable threshold, so it can
accept bit errors in the sync field pattern up to the
threshold level. Furthermore, the correlator window is
programmable. This means that ‘SlotSync’, which
indicates the slot synchronization event, can be detected
only during a certain period (the time window).
Fig.8 Local call switching on the RF-side.
handbook, full pagewidth
MBH712
Rx1
speech buffers
in data memory
Rx2
Tx1
Tx2
RF slots
Fig.9 Schematic of the receiver synchronization part.
handbook, full pagewidth
MBH713
threshold
base/handset
CORRELATOR
(E98A)
Q0 to Q15
EN
R
×
C
D
filtered
data in
R_DATA
(1152 kbits/s)
to serial
receiver logic
FILTER
DPLL
13.824 MHz
XOR
20-BIT SHIFT
REGISTER
Q16 to Q19
SlotSync
correlator
window
SYNC
CHECK
(1010)
DPLL_sync