SE438950B - DIGITAL SIGNAL TRANSVERSAL FILTER - Google Patents

Description

l0 l5 20 25 'Lu: n 40 k. 79078354) according to, which corresponds to a multiple of the modulation rate of the digital signals to be processed. For example, in the above-mentioned publication, a frequency corresponding to the fourfold modulation speed has been chosen as the clock frequency. For the sake of clarity, in the following, the double modulation rate has been selected. The delay time for the individual steps T11, T12 .. Tn then amounts to half of a clock period for the digital signal, corresponding to the duration of the individual pulse.

With the input Es of the digital signal and with the output of each stage, a signal input of a modulator M11, M12 ... Mln is connected, to which the clock signal is applied via connections aï, az ... aïn. Thus, with the aid of this circuit arrangement, as also described in the above-mentioned publication, modulated, ie within a predetermined frequency range, limited digital signals can be generated.

The device according to Fig. 1 requires a delay line with a relatively large number of n-1 steps and n sockets and a correspondingly large number of n modulators. Since the input information pulses only take up half of a modulation period, only half of these modulators are in operation.

With the restriction that n is an even number, a transverse filter according to Fig. 2 is obtained with a considerably lesser degree of complication, since only half the number m of the modulators originally used is required. The duration of the information pulses now corresponds to the clock period, which is equal to the modulation period.

The remaining modulators are switched within this period to two evaluation factors. However, the use of modulators in a still relatively large number leads to a degree of complication and cost, which in many cases is not defensible. In addition, due to the required accuracy, very accurate digital multipliers are required. The object of the invention is thus to provide a transverse filter of the type mentioned in the introduction, which by the greatest possible waiver of the digital multipliers used as modulators leads to a degree of complication and cost.

According to the invention, this problem is solved in that a source of rectangle signals is connected to at least one further address input for spectral formation of the digital signals, so that each of the half-paths of the rectangle signal within a hit period corresponds to an address, and that the reading mine is programmed so that it leaves signals with a certain spectral formation in dependence on the signals present at its inputs.

From this transverse filter according to the invention a band-limited digital signal is emitted, which is also present in digital form.

For generating an analog form, a further development of the transversal filter according to the invention is expedient, in which a digital-to-analog converter is connected to the output of the read-only memory. The digital signals emitted from this transverse filter have, for example, the form (sin X) / x and are thus signals in analog form.

In addition to use as a modulator, the transverse filter according to the invention is particularly useful as a baseband filter for digital signals, the digital signals remaining at the original frequency level. Such a spectral shaping of digital signals is required, for example, in the so-called "roll-off generation", in which the signal is frequency-transformed in such a way that Nyquist flanks arise.

The invention will be described in more detail in the following with reference to the accompanying drawing, in which Fig. 1 shows a known transverse filter, Fig. 1 shows a known transverse filter with multiple use of the modulators and figs. 3 shows a transverse filter according to the invention.

The devices according to Figs. 1 and 2 have already been illustrated in the above description of the state of the art, so they need not be further described here. Det i fíg. The transverse filter shown in Fig. 3 is connected with its input Es to a source for digital signals, the pulse time for these signals amounting to Ts. Connected to the input Es is the signal input of a delay line, which consists of individual steps T31, T32 ... T3 (m-1), in which case m is chosen to be 6. In addition, the input Es for the digital signals is a first address input on a read-only memory ROM connected, the additional address inputs of which are individually connected to the outputs of steps T31 ... T3 (m-1) of the delay line. In addition, a rectangular signal G2 is supplied to the read-only memory ROM via an additional address input Et, the frequency of which corresponds to the bit frequency of the digital signals. In memory ROM, for each possible combination of the signals on the individual address inputs of the memory, a digital output signal is provided, which appears in the form of an 8-bit codeword and is output in parallel on the type of signal output terminals of the memory. To these signal connections are input connections on a post-connected digital-to-analog converter D / A, which converter generates, in a known manner, the input signal appearing in digital form, an output signal appearing in analog form, which is removable at the output A of the transverse filter. This output signal has a shape such as an approximate (sin X) / x oscillation and is thus in analog form. However, the signal content represents the signal content of the digital input signals. In general, in a device controlled at discrete times, in addition to the desired signal spectrum, mostly undesirable sidebands also arise, which can be suppressed by means of a post-connected analog low-pass filter.

Claims (1)

1. 7907833 ~ 3 lëißlaílslït fl y Transverse filter for digital signals with a multi-stage digital delay line connected to the signal input and with a read-only memory (ROM), the first address input of which is connected to the signal input and whose further address inputs are separately connected to outputs of individual (T31, T3Z ... Tšn) of the delay line and whose signal output forms the output of the transversal filter, characterized in that a source of rectangle signals (C) is connected to at least one further address input for spectral formation of the digital signals, so that each of the half-waves of the rectangle signal within a bit period corresponds to the digital signals for an address, and that the read-only memory is programmed to leave signals with a certain spectral formation depending on the signals present at its inputs.