Pulse or digital communications – Synchronizers – Frequency or phase control using synchronizing signal
Patent
1996-01-05
1999-06-29
Chin, Stephen
Pulse or digital communications
Synchronizers
Frequency or phase control using synchronizing signal
341100, 395891, H04L 2538
Patent
active
059178728
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a single chip device for decoding an analog signal carrying digital data representing call identity information.
Telephone companies are increasingly offering call information services. One such service employs signaling, in which the call identity information is transmitted as a CPBFSK (continuous phase binary frequency shift keying) signal between the ringing tones of a calling signal. The CPBFSK signal can typically contain information for services such as calling number delivery (CND), calling identity delivery on call waiting (CIDCW), and calling name delivery (CNAM).
The information contained in the CPBFSK signal is currently extracted by circuitry incorporated in the user equipment or an add-on unit and presented to the user on an LCD display. The CPBFSK signal can contain a wealth of information, and in the future it is likely that increasing amounts of information will become available. It is important to be able to extract this information as useful data words, either simply for display on the local display device or for interfacing with a computer. For example, a telemarketing firm might wish to extract the number of the call party and match it with information in its local database so as to bring up information about the customer prior to accepting an incoming call.
In the prior art, the CPBFSK signal is first demodulated by a CPBFSK demodulator (e.g. Motorola MC145447). The demodulator output is a serial binary data bit stream. The 8-bit data words in the bit stream must be extracted before the information can be further processed by a microprocessor for example.
Data word extraction is typically performed by a universal asynchronous receiver transmitter (UART). The UART may be a discrete unit (e.g. National Semiconductor NS16450), or embedded in a microprocessor (e.g. Intel 8051). The bit stream goes into the serial input of the UART which extracts the 8-bit words and presents them at an 8-bit wide parallel output.
The prior art thus requires a discrete UART, which is generally a relatively complex device having a relatively high power consumption.
An object of the invention is to provide a simplified device capable of decoding CPBFSK signaling that has a low power consumption.
Accordingly, the invention provides a single chip device for decoding an analog signal carrying digital data having a fixed bit rate and consisting of fixed length words of n bits each, where n is an integer, each word being preceded by a start bit and followed by one or more stop bits, comprising an analog demodulator including a switched-capacitor low pass filter for producing from said analog signal at the output of said low pass filter a baseband signal; means for hard limiting said baseband signal to produce a raw bit steam (RDATA); digital means running in synchronism with said analog demodulator for deriving from said raw bit stream a data stream (DATA) containing data bits defining data words and stop and start bits bounding each data word; means for detecting a predetermined identifiable transition in said bit stream preceding each data word; means for generating a clock signal (DCLK) consisting of n clock pulses in response to each detection of said predetermined transition in coincidence with the bits of the data word following said predetermined transition; and means for generating a data ready signal (DR) after the passage of n bits to delineate the word boundary, whereby said data words can be extracted from said bit stream with the aid of said thus generated clock pulses (DCLK) and said data ready signal (DR).
An important aspect of the invention is the extraction of fixed bit length data words from a binary serial bit stream without a discrete UART device, nor the high hardware overhead associated with a full feature UART device included into an integrated circuit performing other functions, nor the need for the UART function to be implemented in microprocessor software.
The circuit in effect provides a three-wire interface that can be implemented on a single chip complete with
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patent: 5313496 (1994-05-01), De Goede
patent: 5394109 (1995-02-01), Simard
Chin Stephen
Deppe Betsy L.
Mitel Corporation
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