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Carrier/Preamble Detection

The Carrier/Preamble Block is a digital Frequency detector Circuit.

It can be used to manage the MAINS access and to detect an incoming signal.

Two are the possible setting:

- Carrier Detection

- Preamble Detection

CARRIER DETECTION: The Carrier/Preamble detection Block notifies to the host controller the

presence of a Carrier when it detects on the RAI Input a signal with an harmonic component close to

the programmed Carrier Frequency. The CD_PD signal sensitivity is identical to the data reception

sensitivity (1mVrms Typ. in Normal Sensitivity Mode).

The CD_PD line is forced to a logic level low when a Carrier is detected.

PREAMBLE DETECTION: The Carrier/Preamble detection Block notifies to the host controller the

presence of a Carrier modulated at the Programmed Baud Rate for at least 4 Consecutive Symbols

(“1010” or “0101” are the symbols sequences detected).

CD_PD line is forced low till a Carrier signal is detected and PLL is in the lock-in range.

To reinforce the effectiveness of the information given by CD_PD Block, a digital filtering is applied on

Carrier or Preamble notification signal (See Control Register Paragraph). The Detection Time Bits in the

Control Register define the filter performance. Increasing the Detection Time reduced the false

notifications caused by noise on main line. The Digital filter adds a delay to CD_PD notification equal to

the programmed Detection Time. When the carrier frequency disappears, CD_PD line is held low for a

period equal to the detection time and then forced high.

Figure 10. CD_PD Timing during RX

Figure 11. Receiving Path Block Diagram

CD_PD

RAI

D03IN1418

Low Pass

Band Pass

PRE-FILTER

IF FILTER

FSK

DEMODULAOR

DIGITAL

FILTER

MIXER

CARRIER/

PREAMBLE

DETECTION

AGC

GAIN

CONTROL

LOCAL

OSC

32

31

Bit 23

Bit 0 -2

Bit 3,4 &14-21

Bit 0-2

RAI

RXFO

Bit 9 & 10

Bit 12 & 13

Carrier Detection

3

RxD

8

CLR/T

1

CD_PD

9

BU

PLL

Bit 3,4

Low Pass

BAND

IN

USE

Bit 3,4

Band Pass

CHANNEL

FILTER

Band Pass

D03IN1419