Status scheme signal processing circuit

1. Field of the Invention

The present invention relates to a signal processing circuit which outputs a signal corresponding to an input signal and, more particularly, to a signal processing circuit using a status scheme.

2. Description of the Related Arts

In order to obtain an output signal having a waveform corresponding to an input signal, a signal processing circuit using a status scheme is used. A desired output signal is obtained on the basis of an OR signal between an ON signal and an OFF signal output from a one-shot pulse circuit at a leading edge and a trailing edge of an input signal and a status signal which is a pulse signal having a predetermined cycle.

In such a circuit, since the input timing of the input signal is not synchronized with the status signal, the output timing of the output signal varies depending on the phase of a status signal obtained when an input signal is received by the circuit. In the circuit which operates by receiving the output signal, the variation in output timing causes jitter generated by phase shift of the signal.

The present invention provides a status scheme signal processing circuit which outputs an output signal by using a mask signal output in synchronism with an input signal at a predetermined timing after the input signal.

In a status scheme signal processing circuit which obtains a desired output signal on the basis of an OR signal between an ON signal and an OFF signal output from a one-shot pulse circuit at a signal leading edge and a signal trailing edge of an input signal and a status signal serving as a pulse signal having a predetermined cycle, as has been described above, the output timing of the output signal varies depending on a phase of the status signal obtained when the input signal changes.

In the present invention, the status scheme signal processing circuit includes a mask signal generator for outputting a mask signal having a predetermined bandwidth T 1 in response to a signal leading edge and a signal trailing edge of an input signal, and using a masking means, said desired output signal is disabled by the mask signal. More specifically, while the mask signal is output, said desired output signal is disabled. In this manner, at the end of the mask signal, said desired output signal is enabled, and said desired output signal is actualy output at this time (i.e., T 1 after the change of the input signal).

FIG. 1 is a circuit diagram of a status scheme signal processing circuit according to the first embodiment of the present invention;

FIG. 2 is a circuit diagram showing the details of a mask signal generator in FIG. 1 ;

FIG. 3 is a time chart showing an operation of the circuit in FIG. 1 ;

FIG. 4 is a time chart showing an operation of the circuit in FIG. 1 ;

FIG. 5 is a circuit diagram of a mask signal generrator in FIG. 1 according to another embodiment;

FIG. 6 is a circuit diagram of the first configuration of a delay circuit in the mask signal generator;

FIG. 7 is a circuit diagram of the second configuration of the delay circuit in the mask signal generator;

FIG. 8 is a circuit diagram of the third configuration of the delay circuit in the mask signal generator;

FIG. 9 is a circuit diagram of the fourth configuration of the delay circuit in the mask signal generator;

FIG. 10 is a circuit diagram of the fifth configuration of the delay circuit in the mask signal generator;

FIG. 11 is a circuit diagram of the sixth configuration of the delay circuit in the mask signal generator; and

FIG. 12 is a circuit diagram of the seventh configuration of the delay circuit in the mask signal generator.

First Embodiment

FIG. 1 shows a status scheme signal processing circuit 10 which represents the first embodiment of the present invention. A signal IN input to an input circuit 11 is input to a one-shot pulse circuit 12 together with a signal inverted by an inverter I 1 . Signals ONEON and ONEOFF corresponding to the respective signals are output from the one-shot pulse circuit 12 . The input signal IN is input to a mask signal generator 13 and a NAND circuit A 1 . The input signal IN is inverted by an inverter I 2 , and the inverted signal is input to an NAND circuit A 2 .

A status signal OSC from the status circuit 14 is input to other input sections of the NAND circuits A 1 and A 2 . Outputs from the NAND circuits A 1 and A 2 are input to one inputs sections of NOR circuits O 1 and O 2 through inverters I 3 and I 4 , and the signals ONEON and ONEOFF are input to the other input sections, respectively.

Outputs from the NOR circuits O 1 and O 2 are input to one input sections of NAND circuits A 3 and A 4 which acts as a masking means through inverters I 5 and I 6 , respectively, and a mask signal MSK from a mask signal generator 13 is input to the other input units. Outputs from the NAND circuits A 3 and A 4 are input to an S terminal and an R terminal of a flipflop circuit 15 through inverters I 7 and I 8 , respectively, and a desired signal OUT is output from an O terminal.

FIG. 2 shows a circuit configuration of the mask signal generator 13 . An input signal IN is directly applied to an input section A of an EXOR, and is input to the other input section B through a delay circuit Q constituted by two inverters and a capacitor C. In this manner, when the input signal N changes its level, delay instantaneously occurs at the input section B, and input levels to both the input sections of the EXOR are different form each other. For this reason, a pulse is output from the EXOR. Since this circuit has a simple configuration, the circuit can be mad compact.

FIG. 3 is a time chart showing an operation of the status scheme signal processing circuit 10 . An OSCON signal and an OSCOFF signal are status signals which are output only while the input signal IN is set at a high level and at a low level. An MON signal is an OR signal between the OSCON signal and the ONEON signal, and an MOFF signal is an OR signal between OSCOFF signal and the ONEOFF signal.

A DON signal is an AND signal between the MON signal and the mask signal MSK, and a DOFF signal is an AND signal between the MOFF signal and the mask signal MSK. The mask signal MSK is a signal which is set at a low level periods T 1 after points of time t 1 and t 3 of the signal leading edge and the signal trailing edge of the input signal IN. Therefore, the DON signal always goes to a low level in a period T 1 after the point of time t 1 . The DOFF signal always goes to a low level in a period T 1 after the point of time t 3 .

As a result, the output signal OUT changes from low level to high level at a point of time t 2 the period T 1 after the point of time t 1 , and changes from high level to low level at a point of time t 4 the period T 1 after the point of time t 3 .

In FIG. 3 , the signal leading edge (t 1 ) and the signal trailing edge (t 3 ) of the signal IN are generated while the status signal OSC is set at a high level. As shown in FIG. 4 , a case in which the leading edge t 1 and the trailing edge t 3 are generated when the status signal OSC is set at a low level.

In this case, immediately after the point of time t 1 , although the OSCON signal is set at a low level, the ONEON signal goes to a high level at least a period T 2 (response time of the one-shot pulse circuit 12 ) after. For this reason, the MON signal also goes to a high level after period T 2 from the point of time t 1 . The mask signal MSK is applied as the MON signal. At this time, when the period T 1 is made longer than the period T 2 , the DON signal always goes to a high level at the point of time t 2 , and the output signal OUT goes to a high level at the point of time t 2 .

When the input signal IN changes from a high level to a low level, as in the operation at the period of time t 1 , the output signal OUT changes from a high level to a low level at the point of time t 4 , which is after period T 1 from the point of time t 3 . In this manner, when the input signal IN changes from a low level to a high level at the point of time t 1 , the output signal OUT changes from a low level to a high level at the point of time t 2 , which is after period T 1 from the point of time t 1 regardless of the level of the status signal OSC. When the input signal IN changes from a high level to a low level at the point of time t 3 , the output signal OUT always changes from a low level to a high level at the point of time t 4 , which is after period T 1 from the point of time t 3 .

Second Embodiment

FIG. 5 shows another circuit configuration of the mask signal generator 13 . This circuit is obtained by adding a delay circuit Q to the same circuit as that of the one-shot pulse circuit 12 . According to this circuit, when an input signal changes to a high level, the upper half of the circuit outputs a pulse (corresponding to ONEON in FIG. 1 ). When the input signal changes to a low level, the lower half of the circuit outputs a pulse (corresponding to ONEOFF in FIG. 1 ). In this manner, since pulses are output from the independent circuits, the bandwidths of both the pulses can be made equal to each other. Since this circuit has the same circuit configuration as that of the one-shot pulse circuit 12 , relative accuracy can be made high.

Third Embodiment

The delay circuit Q indicated by broken lines in FIGS. 2 and 5 is constituted by two inverters and one capacitor. However, the delay circuit Q is not limited to this configuration, and various circuit can be employed as the delay circuit Q. As the delay circuit Q, in FIG. 6 , a simple circuit constituted by a resistor R and a capacitor C is employed, and the entire circuit configuration can be simplified.

Fourth Embodiment

As a delay circuit Q, in FIG. 7 , an NPN transistor NPN and a constant current source X are connected in series with each other, and the capacitor C is connected between the collector and the emitter of the NPN transistor NPN. In this circuit, dependence on a power supply voltage can be decreased.

Fifth Embodiment

As a delay circuit Q, in FIG. 8 , an NMOS transistor NMOS is used in place of the NPN transistor NPN in FIG. 7 . In this circuit, a pattern area can be made smaller than that in FIG. 7 , and a high response speed can also be achieved.

Sixth Embodiment

As a delay circuit Q, in FIG. 9 , a PNP transistor PNP and a constant current source X are connected in series with each other, and a capacitor C is connected between the collector and the emitter of the transistor. This circuit is used when one terminal of the capacitor C cannot be connected to the ground.

Seventh Embodiment

As a delay circuit Q, in FIG. 10 , a PMOS transistor PMOS is used in place of the PNP transistor in FIG. 9 . In this circuit, a pattern area can be made smaller than that in FIG. 9 , and a high response speed can also be achieved.

Eighth Embodiment

As a delay circuit Q, in FIG. 11 , a combination of an NPN transistor NPN and a capacitor C is used as in FIG. 7 . However, in place of the constant current source, a constant current circuit constituted by a constant current source and a current mirror circuit is used. According to this circuit, since a current can be easily changed, a pulse duty can be easily controlled.

Ninth Embodiment

As a delay circuit Q, in FIG. 12 , an NMOS transistor NMOS is used in place of the NPN transistor in FIG. 11 . In this circuit, a pattern area can be made smaller than that in FIG. 11 , and a high response speed can also be achieved.

A signal processing circuit using a status scheme which obtains a desired output signal on the basis of an OR signal between a pulse output from a one-shot pulse circuit at an edge of an input signal and a status signal includes a mask signal generator which outputs a mask signal having a predetermined bandwidth in response to an edge of the input signal, and said desired output signal is masked with the mask signal For this reason, an output signal can be always obtained a predetermined period after an input timing of the input signal.