A means for reducing side lobe signals and noise signals generated in a correlator in N chip positions for correlating a received input signal with a reference signal. The coincidence and non-coincidence indicating signals of first and second halves of the chip positions of the correlator are added together separately and then subtracted one from the other, with the resulting difference signal then being rectified. Such rectified difference signal which contains the side lobe signals and the noise signals but not the desired correlator indicating signal, is subtracted from the total summed and rectified signals generated by all of the N chip positions of said correlator to produce a resultant signal with much of the side lobe signals and the noise signals cancelled out.
A device compares two variable analogue signals, e.g. varying in time, such as audio or video signals. The signals, which are either different or identical but shifted in time, are within a predetermined frequency range. The device includes two parallel channels for processing analogue signals. One of the channels introduces a time shift of one signal with respect to the other, the shift being equal to a 1/4 period at the center frequency of the band. Both channels include in series circuits for transforming the analogue signals into binary logic signals, a logic circuit, a summing circuit for establishing a first and second correlation signal. An adder adds the absolute values of the first and second correlation signals to form a third correlation signal that is substantially independent of any time shift between the analogue signals.
An automatic equalizer includes two wave memories. These wave memories jointly constitute a wave integration memory for storing amplitude information of an input signal. The wave form of input signal to be equalized is divided into fragments along time base, and the amplitude components (analog) of respective fragments are sequentially converted to digital forms in a manner that these fragmentary digital components are alternatively distributed to respective wave memories. For instance, the digital components of odd number fragments are stored in one wave memory, and the digital components of even number fragments are stored in the other wave memory. In this case, the read/write speed of each wave memory may be half of the read/write speed of a prior art wave integration memory which should store all fragments of the digital components. The fragmentary digital components corresponding to the input signal wave form are divided into at least two groups, e.g. an odd group and an even group. A correlator of the automatic equalizer possesses a function for differentiating the fragmentary digital components. The differentiation operation is carried out with the correlation operation by subtracting one fragmentary component of even group from that of odd group.
This invention provides apparatus and methods for obtaining information for aligning a reference signal with a received signal for global positioning satellite receivers which employs at least one correlator for correlating the received signal with the reference signal to generate an accumulated result; the correlator having a comparator to compare the received signal with the reference signal and an accumulator which is either selectively enabled/disabled to prevent overflow errors or is read periodically before an overflow occurs.
A 1 bit/1 bit digital correlator includes a digital multiplier stage and an analog integrator stage, the analog integrator stage having a feedback loop for automatically adjusting a reference voltage for the integrator. The digital multiplier may be an exclusive OR gate which combines two incoming digital sequences and generates a digital output sequence which is divided into two paths in the integrator stage, one path being utilized for obtaining the reference voltage for the integrator and the other path forming a signal path for the integrator. The reference voltage path includes a switch operated by a refresh signal for selectively completing an RC network which is connected to the non-inverting input of an operational amplifier. The signal path includes a low-pass filter connected through a resistor to the inverting input of the operational amplifier, the operational amplifier having a capacitor connected across its output and its inverting input. A feedback loop for resetting the integrator stage is also connected between the output of the first operational amplifier and its inverting input and includes a second operational amplifier having an output selectively connectable through a further switch to the inverting input of the first operational amplifier, and having an inverting input to which a reference starting voltage is supplied and a non-inverting input connected to the output of the first operational amplifier.
A chirp transform correlator having asynchronous operation is made possible by the use of a pair of paralleled signal processing channels to which the unknown signal to be correlated is applied. The two channels include sweeping local oscillators which are interlaced in timing so that any arbitrarily timed unknown input signal will be fully transformed by one or the other of the channels.
