The invention relates to a method of recognizing network-synchronous interfering signals during a data transmission, in which pauses occur between useful signals, with the period of the shortest pause being Tp and the main frequency being f.
A method of this type, and a corresponding device, the two having an analog function, are known.
For the remote control of, for example, devices in the field of entertainment electronics, such as televisions or CD players, or for the remote control of garage doors, the user actuates infrared (IR) transmitters whose IR light is received by a receiving device, and triggers the desired switching process or setting process by pressing a specific IR transmitter key. While IR light is frequently used in such applications, the invention is not limited to this type of information transmission through light, but is also suitable for UV light or visible light, as well as for high-frequency information transmission.
The receiving device receives not only the light transmitted by the IR transmitter, but also the light of other light sources that are fed by the AC network normally employed in households. These interferences are therefore network-synchronous interferences that occur at a single-phase main frequency of, for example, 50 Hz, depending on the interfering station, with a frequency of 50 Hz or 100 Hz.
A fairly large time constant is necessary for recognizing network-synchronous interferences with a relatively high reliability. In the known analog circuits, this time constant requires a relatively large capacitor, which must be disposed, as an additional component, outside of the actual electronic circuit. Fully-integrated solutions without external components are also known; these, however, do not permit a reliable distinction between useful and interfering signals.
It is the object of the invention to create a circuit arrangement that permits all components of the circuit to be housed in a small space, notably requires no voluminous, external capacitor, and, at most, requires the connection of a signal receiver, i.e., an IR detector photodiode for IR signal transmission.
According to the invention, this object is accomplished in that a time span Td is defined, which is shorter than the shortest pauses Tp, but longer than the longest period 1/f or xc2xd f of a network-synchronous interfering station; it is checked whether, during a time period T check greater than Td, preferably a multiple of Td, for example four times Td, pauses occur that are longer than Td; and such an occurrence of pauses is interpreted as the presence of a useful signal without network-synchronous interferences (interfering signals), and no such occurrence of pauses is interpreted as the presence of interferences.
An advantage is that the circuit can operate extensively digitally, so it can be accommodated in a small housing, which means a reduction in costs and new application possibilities (e.g. in video cameras). In contrast, known photomodules require, as a further external component, a further resistor in addition to the aforementioned capacitor.
Another advantage is that the current consumption can be significantly reduced with improved functioning.
Further advantages of the invention are that network-synchronous interfering signals can be unambiguously distinguished from conventionally-used infrared data-transmission signals. This assures a high transmission reliability, and it is possible to transmit data as long as the amplitude of the useful signal is larger than that of the interfering signal.
With the invention, it is also possible to use fewer photomodules and IR pre-amplifiers, which results in cost savings. Because of the digital embodiment, the necessary surface for the circuit (the chip surface in the embodiment as an integrated circuit) can be reduced, which also results in cost savings. The current consumption can be reduced, and can particularly be tailored to the customer""s requirements. Furthermore, the outlay for external circuitry (a capacitor) can be avoided, which contributes to the cost reduction and the small design.
The invention can be applied when the useful signal and the interfering signal meet specific marginal conditions. In accordance with the invention, a distinction is made between an interfering signal and a (not necessarily always present) useful signal based on the occurrence of the signals over time. Network-synchronous interferences (due to fluorescent lamps, electronically-clocked energy-saving lamps, etc.) occur periodically. The repetition period of such an interference is equal to the line period of the used AC network, or equal to half of the line period (in Germany, the repetition period T=20 ms or T=10 ms).
The data formats usually used in IR remote control comprise a block of data bits followed by a pause. The temporal length of the block of data bits is usually 10 ms to 50 ms. The pause duration Tp is normally longer than 30 ms.
The distinction between interfering signals and useful signals is based on the following distinction criterion:
A time Td is defined, which is shorter than the shortest pauses, but longer than the longest period, of a network-synchronous interfering station. The shortest pauses Tp are usually 30 ms long. The longest period of a network-synchronous interfering station is T=20 ms (corresponding to a mains frequency f=50 Hz).
If Td=24 m is selected, the two aforementioned conditions are met. The received signals are now tested with respect to their behavior over time. An interfering station is present if no pauses longer than Td occur in a lengthy time segment. A useful signal is present if pauses longer than Td occur in a lengthy time segment. A digital circuit can be employed to make this distinction.
If it is further ensured that the amplitude of the network-synchronous interferences is smaller at the location of the above-mentioned distinction than the amplitude of the useful signals, in one embodiment of the invention, the use of voltage thresholds varying in magnitude can ensure that only the useful signal is supplied for further evaluation; in accordance with another embodiment of the invention, an amplification regulation can be used in a steady-state regulating procedure to ensure that the interfering signal has such a level that the useful signal can be separated especially simply from the interfering signal based on amplitude, and can be supplied alone for evaluation.
An amplitude of the interfering signals that is smaller compared to the useful signal may be attained through filtering, and/or, in particularly critical cases, an arrangement of the IR signal receiver that is somewhat protected from external light sources, and the user""s use of an IR transmitter having a directional effect, as is provided anyway, and therefore the most target-precise possible transmission to the IR receiver, in which case, of course, the range cannot exceed a predetermined measure.
The invention also relates to a device for recognizing network-synchronous interfering signals during data transmission, in which pauses occur between useful signals, with the duration of the shortest pause being Tp and the mains frequency being f. To accomplish the stated object, means are provided for defining a time span Td that is shorter than the shortest pauses Tp, but longer than the longest period 1/f or xc2xd f, of a network-synchronous interfering station; means are provided for checking whether, during a time period T check greater than Td, preferably a multiple of Td, for example four times Td, pauses occur that are longer than Td; and such an occurrence of pauses is interpreted as the presence of a useful signal without network-synchronous interferences (interfering signals), and no such occurrence of pauses is interpreted as the presence of interferences.
In an embodiment of the invention, an amplitude threshold is provided in the data path of the useful signal, the threshold only permitting an evaluation of the useful signal if its amplitude at the output of a band-pass is larger than that of the interfering signal. This advantageously permits a separation of interferences out of the path of the useful signal.
In an embodiment of the invention, an amplitude threshold is provided in the evaluation path of the interfering signals, the threshold being lower than the aforementioned amplitude threshold in the data path of the useful signal. Even if interferences are present, this provision advantageously permits the evaluation of the interferences such that they cannot be recognized as interferences if the amplitude is sufficiently small.
In an embodiment of the invention, an amplifier whose amplification can be regulated is switched into the signal path of the useful signals and interference signals, and its amplification is regulated such that, in the temporal means, the amplitude of the interfering signal is identical to the threshold value of the amplitude threshold for the interfering signals. This advantageously permits the regulation of the interference amplitude such that it has a virtually constant value that is lower than the first amplitude threshold mentioned above, because of which interferences can be kept out of the path of the useful signal even better.
In an embodiment of the invention, the regulation has a device that increases the amplification of the amplifier when no interferences are recognized, and reduces it when interferences are recognized. This advantageously permits a simple and reliable regulation.
The signals that can be processed with the method and device of the invention can vary greatly. IR remote control systems generally operate at a carrier frequency in the range between 30 kHz and 70 kHz. For the following example, it is assumed that a carrier frequency of 30 kHz is used.
By way of example, it should further be assumed that an IR signal is generated by the user with the aid of his hand-held remote-control device as follows: After an arbitrarily-short pressing of a key that is intended, for example, to switch to another channel in a television, a sequence of ten so-called bursts is generated. Each burst comprises 15 sinusoidal oscillations having a frequency of 30 kHz, followed by a pause corresponding to the length of 30 such rectangular oscillations, and finally, again, 15 rectangular oscillations. The information that is to be transmitted is determined by the mutual spacing between the second and first bursts, the third and second bursts, etc. The ten bursts require a total time of about 10 ms to 50 ms.
Further features and advantages of the invention ensue from the following description of embodiments of the invention in conjunction with the drawing, which shows details that are essential to the invention, and the claims. The individual features can be realized alone, in and of themselves, or in arbitrary combinations in an embodiment of the invention.