CIRCUIT ARRANGEMENT FOR CONVERTING A SERIAL DATA SIGNAL INTO A PARALLEL DATA SIGNAL

Abstract: A serial/parallel converter is proposed which comprises a shift register arrangement (12', 12'' to 12<n>) and an output register arrangement (13', 13'' to 13<n>), each of which comprises n storage devices (12', 12'' to 12<n>; 13', 13'' to 13<n>). Each of the storage devices (13', 13'' to 13<n>) of at least the output register arrangement comprises two data inputs (DP, DS), a selection input (S) for selecting a data input, a clock input (CLK) as well as a data output (Q). The individual clock inputs (CLK) of the storage devices (13', 13'' to 13<n>) receive a serial data signal and the selection inputs (S) receive a frequency-divided clock signal. Second data inputs (DS) of the storage devices (13', 13'' to 13<n>) are connected to the data outputs (Q) of the shift register arrangement (12', 12'' to 12<n>), the first data input (DP) of said storage devices being connected to the own data output (Q). The data signal can be derived in parallel from the data outputs (Q) of the storage devices (13', 13'' to 13<n>).

Description: Circuit arrangement for converting a serial data signal into a parallel data signal. The invention relates to a circuit arrangement for converting a serial data signal into a parallel data signal, comprising a shift register arrangement which consists of n stages, and receives the serial data signal as well as a clock signal associated with the serial data signal and shifts the data of the serial data signal from one stage to another through the shift register arrangement in dependence on the clock signal and outputs in parallel data present on outputs of the stages, comprising an output register arrangement which consists of n stages, which receives in parallel the data output by the shift register arrangement, takes over these data in dependence on a frequency-divided clock signal and outputs these data as a parallel data signal on outputs of the stages, and also comprising a frequency divider arrangement which receives the clock signal associated with the serial data signal and which outputs on an output a frequency-divided clock signal for d e output register arrangement. A circuit arrangement of this kind is known from US 5,223,833. The maximum operating speed of such circuit arrangement, also referred to as a series/parallel converter, is limited essentially by the timing of the clock signals controlling the data entry, because given set-up times and hold times of the registers used in the converter must be complied with and propagation delays must be taken into account. Subject to the condition that the serial data signal and the frequency- divided (load) clock signal have been delayed relative to the serial (data) clock signal by the delay time of one register, for both signals a simultaneous change of state occurs. However, for reliable entry of the relevant data by way of the frequency-divided (load) clock, the relative position of the frequency-divided (load) clock with respect to the serial (data) clock must be corrected. The clock edge of the frequency-divided (load) clock must then be situated exclusively outside the interval determined by the set-up time and the hold time. For temporal correction of the clock signals they could be fed via a given number of series- connected logic gates in order to realise adaptation by way of the gate propagation delay. Because of a tolerance-prone concatenation of the gate propagation delays, however, this step leads to incorrect phase correction of the clock signals, since the sum of the tolerances of the individual set-up and hold times of the registers typically exceeds the minimum feasible system cycle time. Moreover, the fact that such a step requires additional circuitry in the form of a given number of gates is also to be taken into account. Generally speaking, correction of the clock phase positions by way of accurately specified delay lines is very expensive. Moreover, correction of the phase position of the two clock signals is also critical in view of the concatenation of sub-circuits. Inserted specified delay lines preclude a defined clock position relative to the clock at the input side so that, for example in the case of parallel signal branches, careful matching of the clock phases must be carried out. Such matching may even be unreliable in individual cases. It is an object of the present invention to increase the operating speed in a circuit arrangement of the kind set forth. This object is achieved in that each stage of at least the output register arrangement comprises a storage device having a first and a second data input, a selection input for selecting the first or the second data input, a clock input as well as a data output, the clock input of each storage device receiving the clock signal associated with the serial data signal the selection input of each storage device receiving the frequency-divided clock signal, the first data input being connected to the data output of the same storage device and the second data input connected to the data output of the corresponding stage of the shift register arrangement, the parallel data signal being available from the data outputs of the output register stages. The circuit arrangement in accordance with the invention offers the advantage that the clock of the frequency-divided (load) clock signal determines from which of the two data inputs of the storage devices data are taken over. Because of this special connection, in one cycle of the frequency-divided Goad) clock the serial data are taken up in the output register arrangement form the data output of the same stage, so that the signal on the data output remains constant and is taken over in the n* serial (data) clock, via the second input of the shift register arrangement. The phase position of the clock signals thus need not be corrected. The maximum achievable operating speed of the circuit arrangement in accordance with the invention is thus limited only by the operating speed of the shift register and by the set-up and hold times of a device for switching over from one data input to the other data input of the storage device, because clock inputs of the output register arrangement and the shift register arrangement receive the same clock signal. In order to equalize the switching delays of the shift register arrangement and the output register arrangement, it may be effective to construct the stages of the shift register arrangement by means of the same storage devices as the output register arrangement. The first and the second data input of at least the first storage device of the shift register arrangement then receive the serial signal in parallel, whereas the first data input of every subsequent stage is connected to the date output of the directly preceding stage and the second data input can also be supplied with a constant logic signal. In an attractive embodiment of the invention, each storage device consists of a l-to-2 decoder comprising an input and two outputs, a first and a second AND-gate with two inputs and one output each, first inputs of the AND-gates being connected to the two outputs of the l-to-2 decoder and second inputs of the AND-gates being connected to the first and second data inputs, an OR-gate comprising two inputs and one output, d e two inputs of the OR-gate being connected to the two outputs of the two AND-gates, a D-flipflop having a D-input, a clock input and a data output, the D-input being connected to the output of the OR-gate, the clock input receiving the clock signal associated with the serial data signal, and a data signal being available from the data output. The drawing shows an embodiment of the invention which will be described in detail hereinafter. Fig. 1 shows the block diagram of a prior-art series/parallel converter, Fig. 2 shows voltage-time diagrams for the block diagram of Fig. 1, Fig. 3 shows the block diagram of a series/parallel converter in accordance with the invention, Fig. 4 shows voltage-time diagrams for the block diagram of Fig. 3, and Fig. 5 shows the preferred connection of one of the storage devices used in the series/parallel converter in accordance with the invention. Corresponding components are denoted by corresponding references in the Figures. Fig. 1 shows the block diagram of a known series/parallel converter. Via an input terminal 1 of this series/parallel converter, a serial data signal is applied to the input of an n-stage shift register which consists of a series connection of n D-flipflops 2', 2", 2". The serial data signal is present on the D-input of the first D-flip-flop 2'. The output Q of the first D-flipflop 2' is connected to the D-input of the second D-flipflop 2". Analogously, the outputs of the other D-flipflops 2" to 2' are connected to d-inputs of neighbouring D- flipflops. Furthermore, the outputs Q of the D-flipflops 2', 2", 2" are connected to the D- inputs of further D-flipflops 3', 3", 3° which constitute an output register, so that d e serial data signal is converted into an n-bit parallel data signal. The n-bit parallel data signal can be derived from output terminals 4', 4", 4" which are connected to outputs Q of the further D- flipflops 3', 3", 3". The D-flipflops 2', 2", 2 n of the shift register are clocked by a (data) clock signal which is present on a terminal 5 and which is transmitted in parallel with the serial data signal present on die input terminal 1. A frequency-divided (load) clock signal which is generated by a frequency divider 6 is applied to die clock inputs of d e D-flipflops 3', 3", 3" of the output register. The frequency divider 6, receiving die (data) clock signal present on the terminal 5, divides the frequency of the (data) clock signal by n, where n denotes die number of bits per data word. The serial data present on die terminal 1 are shifted from left to right tiirough die individual stages (D-flipflops 2 * , 2" to 2") of die shift register under the control of me (data) clock signal present on die terminal 5. After n clock shift periods, an n-bit data word is present in parallel on die outputs Q of die D-flipflops 2', 2", 2°, which data word is taken up in parallel by die D-flipflops 3', 3", 3° of d e output register, under die control of die frequency-divided (load) clock signal, so as to be output word by word on die output terminals 4', 4", 4". Fig. 2a shows parts of a voltage-time diagram of d e clock signal present on die terminal 5. As has already been stated, diis clock signal is transmitted in parallel with die serial data signal present on the input terminal 1. The associated serial data signal is shown in Fig. 2b. The edges of die serial data signal have been delayed by die propagation delay t, * , with respect to d e ascending edges of the clock signal. The frequency-divided clock signal (Fig. 2c) is assumed to change its state simultaneously widi the edges of d e serial data signals. Because reliable taking over of me data present on d e outputs Q of die shift register is not possible with such a position in time of d e frequency-divided clock signal, d e relative position of die frequency-divided clock (Fig. 2c) widi respect to die serial clock (Fig. 2a) must be corrected in such a manner that the clock edges are situated outside the interval determined by both times t-, (hold time) and t„ (set-up time). The necessary clock phase correction results in increased expenditure for circuitry and adjustment; nevertheless uncertainties remain as regards die taking over of data at high data rates. These drawbacks are avoided in d e series/parallel converter in accordance widi die invention which is shown in Fig. 3. In this series/parallel converter the serial data signal is also applied to d e input of an n-stage shift register. This shift register consists in tiiis example of a series connection of n storage devices 12', 12" to 12" whose special connection will be described in detail widi reference to Fig. 5. The serial data signal applied to die input terminal is present simultaneously on d e inputs DP and DS of d e first storage device 12'. DP denotes a parallel data input and DS denotes a serial data input. The output Q of die first storage device 12' is connected to die input DP of me second storage device 12". Analogously, die outputs of die other storage devices 12" to 12° are connected to die inputs DP of the subsequent storage devices of die shift register. In d e subsequent storage devices 12" to 12", however, d e inputs DS remain open; tiiey are internally connected to a logic L- level. The outputs Q of d e n storage devices 12, 12" to 12" of die shift register are also connected to inputs DS of further storage devices 13', 13" to 13" which constitute die output register. In d e output register d e data signals which can be derived from d e individual outputs Q on die one hand are applied to d e output terminals 4', 4" to 4", wherefrom they can be derived in parallel with a word widtii of n bits, and on d e other hand they are retrocoupled to an input DP of die preceding storage device 13', 13" or 13°. Contrary to die known series/parallel converter (Fig. 1), in the series/parallel converter in accordance widi the invention the clock inputs of die storage devices 12', 12" to 12" of die shift register as well as die clock inputs of die storage devices 13', 13" to 13° of d e output register receive d e (data) clock signal present on the terminal 5. Analogously, all selection inputs S of d e storage devices 12', 12" to 12" and 13', 13" to 13" togetiier receive die frequency-divided clock signal output by die frequency divider 6. like d e frequency divider 6 described widi reference to Fig. 1, die frequency divider 6 provided herein also divides die frequency of d e clock signal present on die terminal 5 by n in order to generate a corresponding word clock signal for d e parallel data take-over. The description of the operation of die series/parallel converter in accordance widi d e invention (Fig. 3) will be preceded by a description of die actual circuit of the storage devices 12', 12" to 12" and 13 * , 13" to 13° used in this example. Fig. 5 shows a preferred embodiment of die storage device. Each of die storage devices essentially comprises a l-to-2 decoder 14 which is controlled by die frequency-divided clock signal, via a terminal S, and which outputs two switching signals via two outputs, said switching signals having eitiier an L-level and a H-level or a H-level and a L-level, depending on die logic level of d e frequency- divided clock signal on the terminal S. The l-to-2 decoder could be realised, for example by means of an IC of the type 74LS139 (Dual 2-to-4 Decoder), only one input and two outputs of which are used for decoding. Each of die storage devices also comprises two AND-gates 15 and 16, each of which comprises two inputs and one output. First inputs of d e two AND-gates 15 and 16 receive die switching signals output by the 1-to- 2 decoder. The second input of die AND-gate 15 is connected to die terminal DP and d e second input AND-gate 16 is connected to die terminal DS. The outputs of d e AND-gates 15 and 16 are connected to die inputs of an OR-gate 17 whose output is connected to d e D- input of a D-flipflop 18. A clock input of die D-flipflop 18 receives d e (serial) clock signal applied to d e terminal CLK. In me storage device shown in Fig. 5 die D-input of a D-flipflop is optionally connected, via a controlled switch (elements 14 to 17), to one of die two input terminals DP and DS. In dependence on die logic level of d e frequency- divided clock signal on die terminal S, either die data signal present on die terminal DP or tiiat present on d e terminal DS is selected. The embodiment of die controlled switch (elements 14 to 17) described widi reference to Fig. 5, evidendy can be replaced by anotiier embodiment. Instead of d e 1- to-2 decoder 14, an amplifier comprising an inverting output and a non-inverting output can be used. In die series/parallel converter in accordance with the invention die storage devices 12', 12" to 12° and 13', 13" to 13" cooperate in such a manner tiiat, as in a shift register, in a cycle of the frequency-divided clock signal die serial data are shifted from left to right (n-l)-times via the input DP of all storage devices 12', 12" to 12° and simultaneously in the storage devices 13', 13", to 13" d e own data contained therein are taken over, tiius remaining unchanged during d e (n-1) clock signals, while by die n* clock signal d e data at the data outputs of die storage devices 12', 12" to 12° are taken over in parallel via die input DS of all storage devices 13', 13" to 13°. Fig. 4a shows d e voltage-time diagram of die serial clock signal present on d e terminal 5. Fig. 4b shows die voltage-time diagram of the serial data signal present on die terminal 1 which has been delayed by die propagation delay t^ wid respect to d e serial clock signal. The edges of the frequency-divided clock signal (Fig. 4c) occur at edge transitions of d e serial data signal so as to take over die data in response to the serial clock in parallel, widi die result tiiat an n-bit parallel data signal is output (Fig. 4d). A customary clock phase correction can, tiierefore, be dispensed with. The maximum operating speed of d e series/parallel converter in accordance widi d e invention is then determined exclusively by the set-up and hold times of the selection input S and die propagation delay in die flipflaps. It will be evident tiiat die shift register can also be implemented by simple storage devices comprising only one data input without switch. The maximum operating speed, however, will not be raised as this speed is furthermore determined by die construction of die storage devices of die output register.

Claims: CLAIMS; 1. A circuit arrangement for converting a serial data signal into a parallel data signal, comprising a shift register arrangement which consists of n stages, which receives die serial data signal as well as a clock signal associated widi the serial data signal, and which shifts die data of die serial data signal from one stage to another through die shift register arrangement in dependence on die clock signal and outputs in parallel data present on outputs of die stages, comprising an output register arrangement which consists of n stages, which receives in parallel the data output by die shift register arrangement, takes over these datas in dependence on a frequency-divided clock signal and outputs these data as a parallel data signal on outputs of the stages, and also comprising a frequency divider arrangement which receives die clock signal associated with die serial data signal and which outputs on an output a frequency-divided clock signal for the output register arrangement, characterized in that each stage of at least die output register arrangement comprises a storage device having a first and a second data input, a selection input for selecting die first or the second data input, a clock input as well as a data output, die clock input of each storage device receiving die clock signal associated widi die serial data signal, the selection input of each storage device receiving die frequency-divided clock signal, die first data input being connected to die data output of die same storage device and the second input connected to die data output of die corresponding of die shift register arrangement die parallel data signal being available from die data outputs of die output register stages. 2. A circuit arrangement as claimed in Claim 1, characterized in tiiat each of die storage devices comprises a D-flipflop widi a D-input which, via selection circuit controlled by die frequency-divided clock signal, receives either the data signal present on the first data input or die data signal present on die second data input. 3. A circuit arrangement as claimed in die Claim 1 or 2, characterized in tiiat each storage device consists of a l-to-2 decoder comprising an input and two outputs, a first and a second AND-gate widi two inputs and one output each, first inputs of die AND- gates being connected to die two outputs of die l-out-of-2 decoder and second inputs of die AND-gates being connected to the first and second data inputs, an OR-gate comprising two inputs and one output, the two inputs of die OR-gate being connected to die two outputs of die two AND-gates, a D-flipflop having a D-input, a clock input and a data output, die D- input being connected to die output of die OR-gate die clock input receiving, die clock input receiving die clock signal associated widi die serial date signal, and a data signal being available from die data output.

Inventors: ZIRNGIBL WOLFRAM, ZIRNGIBL, WOLFRAM
Applicants: PHILIPS ELECTRONICS NV, PHILIPS NORDEN AB, PHILIPS PATENTVERWALTUNG, PHILIPS ELECTRONICS N.V., PHILIPS PATENTVERWALTUNG GMBH
Application year: 1995
Main classification: H03M9
IPC codes: H03M9