Parallel-Series Converter

1. Field of the Invention

The invention relates to a parallel-series converter having a plurality of parallel inputs and comprising a combining arrangement having a plurality of inputs equal in number to the plurality of parallel inputs of the parallel-series converter, and a series output.

2. Description of the Related Art

In digital transmission systems it often happens that the wish is felt for converting n parallel spatially separated bit streams of p bits/second each, into one serial bit stream, without loss of information. In this serial bit stream the individual n but streams are now separated in time. This procedure is known as the parallel-series conversion, the serial digital signal having a frequency equal to n.times.p bits/second.

In digital transmission systems it is normal practice to effect such parallel-series conversion only with the aid of active digital circuits. These active circuits are integrated with further portions of the transmission system on, for example, a semiconductor body. The use of integrated active digital circuits increases the total required dissipation of the semiconductor body. This may cause design problems in connection with the maximum permissible dissipation of the semiconductor body.

The invention has for its object to provide a solution to the above problem and is characterized in that each parallel input is connected via the series arrangement of a terminating impedance and a transmission line to a respective one of the inputs of the combining arrangement, the time delays of the individual transmission lines having respective different magnitudes according to an arithmetical progression, the junction between each terminating impedance and the associated transmission line being connected to a short-circuited transmission line having a length .lambda./2, where .lambda. is the wavelength of the desired output frequency of the parallel-series converter, each original pulse as applied to the input of the relevant short-circuited transmission line appearing again after a short period of time with a delay and in inverted form at the same input, such that the original pulse, during the time it is overlapped by the inverted pulse, is wholly or substantially wholly, eliminated.

In a parallel-series converter according to the invention, use is made predominantly of passive elements to effect the parallel-series conversion. As a result, the additional dissipation due to the parallel-series converter and added to the total dissipation is drastically reduced.

The invention will now be described in greater detail by way of example with reference to the accompanying drawings, in which

FIG. 1 shows an embodiment of a parallel-series converter according to the invention; and

FIG. 2 shows a time diagram to explain the operation of the parallel-series converter.

In the parallel-series converter shown in FIG. 1, the parallel inputs are constituted by the terminals 31, 32 and 33 and the information is applied to these terminals by sources 1, 2 and 3. The input 31 is connected to a first input 41 of a combining arrangement I via the series arrangement of a terminating impedance 4 and a transmission line 7. The input 32 is connected to a second input 42 of the combining arrangement I via the series arrangement of a terminating impedance 5 and a transmission line 8. The input 33 is connected to a third input 43 of the combining arrangement I via the series arrangement of a terminating impedance 6 and a transmission line 9. The input 41 is connected to a terminating impedance 13 and also to the base electrode of a transistor 17. The input 42 is connected to a terminating impedance 14 and also to the base electrode of a transistor 18. The input 43 is connected to a terminating impedance 15 and also to the base electrode of a transistor 19. The collectors of the transistors 17, 18 and 19 are connected to the positive pole (+) of a supply voltage and also via a resistor 21 to an output 23 of the parallel-series converter. The collector of a transistor 20 is connected to the output 23 of the parallel-series converter. The emitters of the transistors 17, 18, 29 and 20 are connected in common to a point 24 of constant potential via a resistor 22. The base electrode of the transistor 20 is connected to a source of reference voltage 16. The junction point of the terminating impedance 4 and the transmission line 7 is connected to a short-circuited transmission line 10. The junction of the terminating impedance 5 and the transmission line 8 is connected to a short-circuited transmission line 11. The junction of the terminating impedance 6 and the transmission line 9 is connected to a short-circuited transmission line 12.

A digital signal, which is of the shape shown in FIG. 2a, is applied to the inputs of the parallel-series converter. The widths of the pulses applied to the inputs are limited, such as described, for example, in U.S. Pat. No. 3,515,995. This is necessary as otherwise loss of information would occur in the parallel-series converter. In addition, negative reflection pulses are produced at the input of the short-circuited transmission line, as shown in FIG. 2b. These reflection pulses are unwanted and are suppressed in the combining arrangement I with the aid of the transistor 20 and the reference voltage 16 source. Mutatis mutandis it is alternatively possible to utilize the negative pulse and to eliminate the positive pulse. A further method of suppressing the unwanted reflection pulses is, for example, to provide a diode between the short-circuited transmission line 10 and the transmission line 7. This diode is arranged such that only the positive pulses are allowed to pass to the transmission line 7. FIG. 2c shows by way of example a voltage variation of the pulses produced by the source 1. FIG. 2d shows by way of example a voltage variation of pulses produced by the source 2 and FIG. 2e shows the voltage variation of the pulses produced by source 3.

In response thereto, the three parallel bit streams (1, 1, 0), (1, 1, 1) and (0, 1, 1) appear in this succession at the inputs 31, 32 and 33. Due to the action of the respective short-circuited transmission lines 10, 11 and 12, the pulse widths of the pulses from these parallel bit streams are limited as is shown in FIG. 2b. The three parallel bit streams of three bits each are thereafter applied to the inputs 41, 42 and 43 of the combining arrangement I. The transistors 17, 18, 19 and 20 together form a multiple OR-gate. With the aid of the transistors 17, 18 and 19 the three parallel bit streams are arranged time-sequentially as is shown in FIG. 2f. The emitter of the transistor 20 is adjusted to such a potential with the aid of the reference voltage source 16 that the above-mentioned negative reflection pulses as shown in FIG. 2b are blocked and do not occur at the output 23 of the parallel-series converter. The repetition rate T.sub.s of the serial pulses at the output 23 is equal to 1/3 T, where T is the repetition rate of the pulses at the inputs 31, 32 and 33 of the parallel-series converter. The time delays .tau. of the transmission lines 7, 8 and 9 are adjusted such that the pulses of limited widths which are obtained, appear one after the other at the respective inputs 41, 42 and 43. A possible choice of these time delays is, for example, .tau.(7)=0, .tau.(8)=T.sub.s and .tau.(9)=2T.sub.s, see FIG. 2f. These transmission lines can be realized, depending on the frequency range in which the digital transmission system is operated, with the aid of printed conductors, cables, microstrips etc.