Receiver and decoder

#Many receivers and receiver decoders have been used to receive a modulated signal so that the receiver output may control some load remote from the transmitter. In remotely controlled devices, radio controlled garage door openers, as an example, there may be an insufficient number of carrier frequencies and modulation frequencies with which to provide sufficient codes so that a neighborhood having many radio controlled garage door operators will incur false operation. There may be interference between two closely adjacent receivers wherein a strong signal from a closely positioned transmitter or the radiation from one of the receivers could energize a relay in a receiver even when the carrier and modulation frequencies in the transmitter and receiver are not the same. One solution was to provide two modulation frequencies both modulating the carrier at the same time and then the receiver had to be on the same code of three different frequencies namely, the carrier and the two modulation frequencies in order to respond to such transmitted signal. Due to the economic limitations, the number of carrier frequencies available was not large. Also the number of modulation frequencies available which were not integral multiples, that is, harmonics of one another, was also not large so that the number of possible codes might be limited to two or three hundred, for example. Often this was insufficient to prevent unwanted actuation of the incorrect receiver and thus opening of a garage door other than the one intended.

#One possible solution was to utilize a carrier wave turned on and off by a digital signal. First and second digital signals of two to one ratio of frequencies in phase agreement were utilized and were combined to provide either a short pulse or a long pulse. This gave a pulse train of 9 or 10 pulses of varying pulse widths to turn on and off a carrier wave. A synchronization period of the absence of pulses indicated the end of the message. This message was repeated continuously by the transmitter. If the receiver was on the same code, that is, the same carrier frequency and the same sequence of short and long pulses, then the receiver would have an output and the remotely controlled load would be actuated.

#These prior attempts at a receiver decoder had the deficiencies of an insufficient number of codes to be transmitted so as to avoid improper actuation of the receiver. There have been reports that the digital control system has been false triggered by noise such as a teletype signal which also has short and long pulses in its signal. Also such prior digital control system had a lack of a preamble pulse pattern to assure exclusivity of the transmitted and received signal. Also such prior digital system could be easily false triggered by a noise pulse so that the entire train of pulses was dumped at the wrong time.

#FIG. 1 is a schematic diagram of a receiver according to the invention;

#FIG. 2 is a diagram of the modulation patterns or logic conditions of bits on the carrier wave;

#FIG. 3 is a diagram of an alternative modulation pattern;

#FIG. 1 is a schematic diagram of a receiver 25 incorporating the invention. The receiver 25 includes generally a carrier amplifier and detector circuit 26, a decoder circuit 27 and an output circuit 28. The carrier amplifier and detector circuit 26 may receive incoming signals from a pair of conductors or as shown may receive it from an antenna and hence be a radio receiver. In such case the carrier amplifier may include any one of many usual forms, for example, a superregenerative amplifier circuit and a detector to detect the modulation signal on the carrier and supply it to the decoder circuit 27 on a raw data line 29.

#The decoder circuit 27 operates at low power levels and conveniently may be made as an integrated circuit on one semiconductor chip. This decoder 27 is for use with an encoded data train which has three different modulation patterns or logic conditions of bits. A bit is defined in this application as being a definite period of time and a first bit or bit pattern is defined as X cycles of a first higher modulation frequency, a second bit pattern being Y equal (X/m) cycles of a second lower modulation frequency, and a third bit pattern being the series combination of nX cycles of said first frequency and (1-n) (X/m) cycles of said second frequency, where X and Y are different numbers, n is a number between zero and one, and m is an integer other than one. These first and second modulation frequencies may be in the form of a square wave and the logic bits may be square wave cycles so that the decoder circuit 27 may be considered a digital circuit.

#The output circuit 28 amplifies the output from the decoder 27 to greater power levels and when there is an output from the decoder 27 at terminal 30, a driver transistor 31 will be turned on to energize a relay 32 closing contacts 33. These may be used to control an external load. The receiver 25 is one operable as a remotely controlled receiver so that when a given signal is sent by the remotely positioned transmitter with a particular carrier and encoded data train, and the receiver 25 responds to this particular carrier and encoded data train, then the contacts 33 will be closed to control the remotely controlled load. As an example this may be a garage door operator to open and close a garage door.