Demodulators – Pulse or interrupted continuous wave demodulator
Reexamination Certificate
1999-11-17
2002-01-01
Kinkead, Arnold (Department: 2817)
Demodulators
Pulse or interrupted continuous wave demodulator
C359S199200, C359S199200, C455S214000, C375S219000, C375S340000
Reexamination Certificate
active
06335658
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a demodulation circuit for infrared data. More particularly, the invention relates to a demodulation circuit which can reproduce infrared data and serial data.
2. Description of the Related Art
According to the development of electronic industries in the recent years, data communication between a plurality of electronic equipments has been spreading as a normal technology. Particularly, in case of a portable terminal or notebook PC (personal computer), for which portability is given importance, reduction of weight has been attempted by eliminating an external storage medium, such as a floppy disk drive, an external magnetic disk driven or so forth. Therefore, the function for communicating with other equipments has been the essential function for such type of equipments, such as portable terminal, notebook PC or so forth. Currently, in addition to a serial communication port typically represented by that according to the RS232C standard, an infrared communication port which does not require cable connection, has been equipped as standard component.
As a standard for infrared communication, IrDA (Infrared Data Association) has been standardized. However, this IrDA standard is adapted for opposing communication in one to one basis to encounter a problem in low freedom in the sense of convenience of use. This problem has been resolved by infrared standard called IrBUS established on Jan., 1998. In the portable terminal or notebook PC equipped with the IrBUS, it becomes necessary to effectively realize hardware which also have communication functions in the conventional serial port.
On the other hand, conversion from an infrared ray into an electric signal has been realized by an analog circuit, and has been commercialized by semiconductor manufacturers as infrared modules. Since no standard has been established for the infrared module per se, interfaces with the electrical signal are different in respective companies. For example, in IRDA or IrBUS, an infrared ray in which data is modulated with a given carrier frequency, has been used. The electrical signal output from the infrared modules is reproduced as a digital signal with modulated carrier frequency or as a serial signal from which the carrier frequency is removed. These reproduction signal are different in transfer rate of data to inherently require serial/parallel conversion circuit dedicated thereto upon outputting data with serial/parallel conversion to a bus. Such serial/parallel conversion circuit is referred to as Universal Asynchronous Receiver/Transmitter (UART) to perform sampling of input sampling data at a sampling rate corresponding to a data rate, then to perform serial/parallel conversion and thus to output the data to the bus at the predetermined timing. Therefore, the demodulation circuit of the electric signal requires dedicated circuit specified therefore to inherently cause increasing of the scale of the circuit.
The Circuit construction in the prior art is illustrated in FIG.
14
. In
FIG. 14
, an infrared input
1
receives a signal output from an infrared module receiving an infrared signal according to IrDA standard, for example. A serial input
2
receives a signal (i.e. serial data) output from a serial port, such as RS-232C or so forth or the infrared module receiving the infrared signal according to IrBUS standard. The infrared input
1
is connected to a system bus
6
via an UART
5
B after demodulation by a demodulation circuit
4
. The serial input
2
is connected to the system bus
6
only via the UART
5
A. Here, the demodulation circuit
4
is designed for converting (i.e. demodulating) the infrared signal into the serial data. As can be clear from
FIG. 14
, when the demodulation circuit
4
receives the serial signal through the serial input
2
and the UART
5
B can provide an output, the UART
5
A can be eliminated. However, since the infrared input and the serial input have mutually different communication protocol, correct serial/parallel conversion cannot be performed in the UART
5
B, and the UART
5
B thus cannot output the correct data to the bus unless the signal output from the demodulation circuit can be identified as either the serial data or the infrared data. Namely, unless the signal output from the demodulation circuit can be identified as either the serial data or the infrared data, control by the communication software becomes impossible. Therefore, the UART
5
A and
5
B respective have dedicated design adapting to respective communication protocol and the user has to manually perform system setting of the protocol of the reception data preliminarily upon reception. The system performs selection of the UART on the basis of the setting and performs control of the communication software.
As a typical demodulation technology of the infrared input, there is a method to perform demodulation of the infrared input by a low pass filtering (LPF) process by means of a Finite Impulse Response (FIR) type digital filter. This method sets a pass-band by a filter coefficient of the digital LPF to reproduce an objective signal. A tap coefficient of the filter and a result of superimposing are processed by respective one bit. Operation timing is shown in FIG.
15
. In
FIG. 15
, an impulse response corresponding to a pulse P
1
input from the infrared input terminal
1
is executed by the LPF
9
to obtain a pulse response A. In the similar manner, a pulse response B corresponding to a pulse P
2
input from the infrared input terminal
1
and a pulse response C corresponding to a pulse P
3
can be obtained. Then, result of superimposing of the pulse responses A to C is reproduced as a demodulated output.
In such method, while it is possible to input the serial data from the infrared input terminal, it is not possible to distinguish whether the infrared data or the serial data is received, from the demodulated output. As shown in
FIG. 14
, the demodulated output is supplied to the superior information processing system, such as a CPU (not shown) or so forth via a system bus
6
and then data processing is performed.
For example, which both of the infrared data and the serial data are subject to serial-to-parallel (S/P) conversion process, sampling frequencies required for the S/P conversion process are different in both data. Therefore, it becomes necessary to distinguish whether the input signal is the infrared data or the serial data. On the other hand, in case of the infrared data, since error correction, CRC operation or so forth becomes necessary, discrimination of the input signal between the infrared data or the serial data becomes necessary even in this process. Therefore, upon practical use, it becomes necessary to fix whether the infrared data or the serial data is to be used. However, in the foregoing example, since automatic discrimination between the infrared data and the serial data cannot be performed, automatic switching by software cannot take place.
Here, as an example of another conventional demodulation circuit, a circuit construction is shown in
FIG. 16
, and operational timing is shown in FIG.
17
. In this circuit, a method to preliminarily set a photo receiving range of the infrared input and to eliminate the input out of the photo receiving range from a result of the count of the pulse width of the input infrared ray, is employed. In
FIG. 16
, the infrared input is input to the LPF
9
and the pulse width counting portion
21
, and the pulse width of the reception data is counted with a high speed clock. A result of counting of the pulse width is checked as to whether it falls within a predetermined value or not, by a photo reception error judgment portion
22
to perform reproduction of data.
In the timing chart shown in
FIG. 17
, during a period where the infrared input is “H”, counting of the pulse is performed. Then, if a result of counting of the pulse width falls within the photo receiving range, the data is judged as normal, and otherwise output as pho
Foley & Lardner
Kinkead Arnold
NEC Corporation
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