FREQUENCY MULTIPLYING CIRCUIT

Abstract: A frequency multiplying circuit for a disc controller includes a first time counting unit (2l) responsive to input pulse signals (S(CLK)) for producing a first detection signal when a HIGH level period of the input pulse signals (S(CLK)) is longer than a predetermined length, a second time counting unit (22) responsive to the input pulse signals (S(CLK)) for producing a second detection signal when a LOW level period of the input pulse signals (S(CLK)) is longer than a predetermined length, and a pulse generation determining unit (3) responsive to the produced first and second detection signals for realizing a SET state by the produced first detection signal and realizing a RESET state by the produced second detection signal to generate gate signals (Q, ). First and a second pulses are generated in gates (4l, 42) responsive to the gate signals (Q, ), and a rising or falling edge of the input pulse signals (S(CLK)) to deliver frequency multiplication of the input pulse signals (S(CLK)) is prohibited when the frequency of the input pulse signals is higher than a predetermined frequency to prevent unacceptably short LOW level periods of the frequency multiplied signals.

Description: The present invention relates to a frequency multiplying circuit. The frequency multiplying circuit according to the present invention can be applied, for example, in read signal generation in a disc controller used, for example, for a floppy-disc controller of a personal computer. In general, digital data, with the FM type modulation and the modified FM type (MFM type) and stored in a disc memory as an external memory of a computer is reproduced by a reproducing device having a phase locked loop circuit, a frequency multiplying circuit, and a data reading circuit. The phase locked loop circuit extracts a clock signal from the reproduced signal. The frequency of the extracted clock signal is multiplied by two by the frequency multiplying circuit. The frequency multiplied signal is supplied as a data reading clock signal to the data reading circuit. The data reading circuit reads the clock bits and the data bits from the regenerated signal by using the data reading clock signal. Usually, in the prior art frequency multiplier circuit used for the disc controller, the oscillation frequency in the phase locked loop circuit is subject to considerable changes in a lock-in process with regard to a regenerative signal, so that the frequency of the clock signal is subject to considerable changes. As the frequency of the clock signal increases, the lengths of LOW level potential periods become quite short, causing the frequency of the output signal to be high. This high frequency of the output signal causes an abnormal operation of the data reading circuit, and prevents a data reading circuit from performing a normal operation. Accordingly, problems have occurred in that the clock bits and data bits cannot be read, and that an error signal indicating an error in the data reading cannot be generated. According to this invention a frequency multiplying circuit comprises: a reference input frequency; a first time counting means responsive to input pulse signals for producing a first detection signal when said input pulse signals maintain a HIGH level for a time greater than that required for a predetermined number of periods of the reference input; a second time counting means responsive to the input pulse signals for producing a second detection signal when said input pulse signals maintain a LOW level for a time greater than that required for a predetermined number of periods of the reference input; a pulse generation determining means responsive to said produced first and second detection signals for realizing a SET state by said produced first detection signal and realizing a RESET state by said produced second detection signal to generate gate signals; a first pulse generating means responsive to one of said generated gate signals for detecting rising edges of said input pulse signals to generate first pulses which are substantially synchronous with said rising edges; a second pulse generating means responsive to the other of said generated gate signals for detecting falling edges of said input pulse signals to generate second pulses which are substantially synchronous with said falling edges; said first and second pulses being delivered as frequency multiplied signals of said input pulse signals; whereby the frequency multiplication of said input pulse signals only occurs when the period of said input pulse signals exceeds the time required for a predetermined number of periods of the reference input. A particular example of a frequency multiplier circuit in accordance with this invention will now be described and contrasted with the prior art with reference to the accompanying drawings; in which:- Figure l is a circuit diagram of a prior art disc controller including a frequency multiplier circuit; Figure 2 shows waveforms of the signals in the prior art disc controller; Figure 3 is a circuit diagram of a frequency multiplying circuit according to a preferred embodiment of the present invention; Figures 4 to 7 show waveforms of the signals in the frequency multiplying circuit shown in Figure 3 under four conditions; and, Figure 8 shows a data latch circuit to which the output signal of the frequency multiplying circuit of Figure 3 is sent. Before describing the preferred embodiments of the present invention, a prior art disc controller including a frequency multiplier circuit is described with reference to Figures l and 2. The prior art disc controller shown in Figure l includes an input terminal l00, a data reading circuit l0l, a phase locked loop circuit l02, and a frequency multiplying circuit l03 having a delay circuit l07, an inverter l08, an exclusive OR gate l06, and an inverter l09. The clock signal S(l02) as the output of the phase locked loop circuit l02 is supplied to one input terminal of the exclusive OR gate l06 and the delay circuit l07. The output of the delay circuit l07 is supplied to the inverter l08 which produces the inverted signal S(l08) to be supplied to the other input terminal of the exclusive OR gate l06. The output of the exclusive OR gate l06 is supplied to the inverter l09 which produces the inverted signal S(l09) to be supplied to one input terminal of the data reading circuit l0l. The waveforms of the signals S(l02), S(l08), and S(l09) are shown in Fig. 2. The pulses S(l09) are produced at the rising edges and the falling edges of the clock pulses S(l02). Thus, the frequency of the pulses S(l09) is twice that of the pulses S(l02). In practice, in the circuit shown in Fig. 1, the oscillation frequency in the phase locked loop circuit l2 is subject to considerable changes in a lock-in process with regard to a regenerative signal, so that the frequency of the clock signal S(l02) is subject to considerable changes. As the frequency of the clock signal S(l02) increases, as shown in right part of the waveform (l) in Fig. 2, the lengths of the LOW level potential periods Ll, L2, and L3 become quite short, as shown in the right part of the waveform (3) in Fig. 2, causing the frequency of the output signal S(l09) to be considerably high. This high frequency of the output signal S(l09) will cause an abnormal operation of the data reading circuit l0l. The supply of the signals S(l09), shown in the right part of the waveform (3) in Fig. 3, having short intervals Ll, L2, and L3, to the data reading circuit l0l will prevent the data reading circuit l0l from attaining a normal operation. The arrangement of a frequency multiplying circuit according to a preferred embodiment of the present invention is shown in Fig. 3. The circuit of Fig. 3 includes a clock signal inputting terminal ll, a reference signal inputting terminal l2, an inverter l3, a first shift register 2l as a first timing means, a second shift register 22 as a second timing means, an S-R flip-flop circuit 3 as a gating timing determination means, AND gates 4l and 42, delay circuits 5l and 52, inverters 6l and 62, AND gates 7l and 72, an OR gate 8l, and an output terminal 82. Clock signals S(CLK) from a phase locked loop circuit are supplied through the input terminal ll to the data terminal D and the reset terminal R (inverted R) of the shift register 21, the inverter 13, and one input terminal of the AND gate 41. The output of the inverter l3, which is an inversion of the clock signals, is supplied to the data terminal D and the reset terminal R of the shift register 22, and the AND gate 42. The clock signal S(CLK) has a frequency of, for example, 500 kHz. A reference signal S(REF) having a predetermined constant frequency is supplied through the input terminal l2 to the clock input terminals CK of the shift registers 2l and 22. The reference signal S(REF) is not synchronized with the clock signal S(CLK). In each of the shift registers 2l and 22, the RESET state is cancelled when the potential of the reset terminal R becomes HIGH level. After the cancellation of the RESET state, each time the reference signal pulse S(REF) is supplied to the clock input terminal CK, the HIGH level clock signal S(CLK) (or the inverted clock signal S(CLK) ) is taken into the shift register, and the taken clock signal S(CLK) (or the taken inverted clock signal S(CLK) ) is shifted in the shift register, and the delayed clock signal (or the delayed inverted clock signal) delayed by, for example, 4 cycle periods of the reference signal S(REF), is delivered from the output terminal of the shift register. When the potential of the reset terminal R becomes LOW level, the shift register is in the RESET state and the potential of the output terminal of the shift register becomes LOW level. Examples of the waveforms of the signals appearing in the circuit of Fig. 3 are shown in Figs. 4, 5, 6, and 7. For example, the reference signal S(REF), the input clock signal S(CLK), the inverted input clock signal S(CLK) , the output S(2l) of the shift register 2l, the output S(22) of the shift register 22, the Q output S(3, Q) of the flip-flop circuit 3, the Q output S(3, Q ) of the flip-flop circuit 3, the output S(4l) of the AND gate 4l, the output S(6l) of the inverter 6l, the output S(42) of the AND gate 42, the output S(62) of the inverter 62, the output S(7l) of the AND gate 7l, the output S(72) of the AND gate 72, and the output S(8l) of the OR gate 8l are shown in Fig. 4. The shift register 2l delivers a HIGH level set signal S(2l) when the HIGH level period of the input clock signal S(CLK) exceeds 4 cycle periods of the reference signal S(REF), and the delivered signal S(2l) is supplied to the set terminal S of the SR flip-flop circuit 3. The shift register 22 delivers a HIGH level reset signal S(22) when the LOW level period of the input clock signal S(CLK) exceeds 4 cycle periods of the reference signal S(REF), and the delivered signal S(22) is supplied to the reset terminal R of the SR flip-flop circuit 3. The internal state of the flip-flop circuit 3 is reversed by a set signal and a reset signal incoming through the set terminal S and the reset terminal R, so that the signal S(3, Q) from the Q terminal is supplied to one input terminal of the AND gate 42 and the signal S(3, Q ) from the Q terminal is supplied to one input terminal of the AND gate 4l. The AND gate 4l passes the clock signal S(CLK) during the period in which the potential of the signal S(3, Q ) is HIGH level. The output clock signal of the AND gate 4l is supplied to one input terminal of the AND gate 7l and the delay circuit 5l. The output S(5l) of the delay circuit 5l, which is delayed by a predetermined time of, for example, 2 cycle periods of the reference signal S(REF), from the input S(4l) of the delay circuit 5l is inverted by the inverter 6l. The output S(6l) of the inverter 6l is supplied to the other input terminal of the AND gate 7l. Accordingly, after the LOW level period of the input clock signal S(CLK) exceeds 4 cycle periods of the reference signal S(REF) and the potential of the Q output S(3, Q ) of the flip-flop circuit 3 becomes HIGH level, when the potential of the clock signal S(CLK) rises, the AND gate 7l produces a first pulse S(7l) having a length of, for example, 2 cycle periods of the reference signal S(REF). The produced first pulse S(7l) is supplied to the OR gate 8l. The AND gate 42 passes the inverted clock signal S(CLK) during the period in which the potential of the signal S(3, Q) is HIGH level. The output inverted clock signal of the AND gate 42 is supplied to one input terminal of the AND gate 72 and the delay circuit 52. The output S(52) of the delay circuit 52, which is delayed by a predetermined time of, for example, 2 cycle periods of the reference signal S(REF), from the input S(42) of the delay circuit 52 is inverted by the inverter 62. The output S(62) of the inverter 62 is supplied to the other input terminal of the AND gate 72. Accordingly, after the HIGH level period of the input clock signal S(CLK) exceeds 4 cycle periods of the reference signal S(REF) and the potential of the Q output S(3, Q) of the flip-flop circuit 3 becomes HIGH level, when the potential of the clock signal S(CLK) falls, the AND gate 72 produces a second pulse S(72) having a length of, for example, 2 cycle periods of the reference signal S(REF). The produced second pulse S(72) is supplied to the OR gate 8l. The OR gate 8l to which the first and second pulses S(7l) and S(72) are supplied produces a pulse signal S(8l) which is delivered from the output terminal 82. In accordance with the sequence of the levels of the potential of the input clock signal S(CLK), the following four examples of the operation of the frequency multiplying circuit of Fig. 3 are considered. (Case-l) Each of the HIGH level period and the LOW level period of the potential of the input clock signal S(CLK) exceeds 4 cycle periods of the S(REF). The waveforms of the signals in Case-l are shown in Fig. 4. In the case of Fig. 4, each of the HIGH level potential period tl and the LOW level potential period t2 of the S(CLK) exceeds 4 cycle periods of the S(REF). The setting and the resetting of the flip-flop circuit 3 are carried out at 4 cycle period of the S(REF) after the rising and the falling of the S(CLK), as shown in S(2l) and S(22). The Q and Q outputs of the flip-flop circuit 3 are as shown in S(3, Q) and S(3, Q ). The outputs of the AND gates 4l and 42 are as shown in S(4l) and S(42). The outputs of the delay circuits 5l and 52, which are delayed by 2 cycle periods of S(REF) from the inputs, are as shown in S(6l) and S(62). The outputs of the AND gates 7l and 72 are as shown in S(7l) and S(72). Thus, the output signal ql, q2, ... of the OR gate 8l is as shown in S(8l). Accordingly, in the case of Fig. 4, the frequency of the output signal S(8l) is twice that of the input clock signal S(CLK). (Case-2) The length of the preceding LOW level period of the potential of the input clock signal S(CLK) exceeds 4 cycle periods of the S(REF), and the length of the present HIGH level period of the potential of the input clock signal S(CLK) is less than 4 cycle periods of the S(REF). The waveforms of the signals in Case-2 are shown in Fig. 5. In the case of Fig. 5, the preceding LOW level periods t2, t4 exceed 4 cycle periods of the S(REF), and the present HIGH level periods t3, t5 are less than 4 cycle periods of the S(REF). The input clock signal S(CLK) is not delivered from the shift register 2l. After 4 cycle periods of the S(REF) from the falling of the S(CLK), the reversal of the outputs of the flip-flop circuit 3 does not take place, so that the potential of the Q output S(3, Q ) of the flip-flop circuit 3 is maintained at a HIGH level. The outputs of the AND gate 4l, the inverter 6l, the AND gate 42, the inverter 62, the AND gate 7l, and the inverter 72 are as shown in S(4l), S(6l), S(42), S(62), S(7l), and S(72). The AND gate 7l delivers the output pulses at the risings of the input clock pulses S(CLK), but the AND gate 72 does not deliver the output pulses. Therefore, the OR gate 8l delivers only the signals q3, q4, ... as shown in S(8l). Accordingly, the frequency of the output signal is not multiplied from the frequency of the input clock signal but is maintained at the same levels as the frequency of the input clock signal. (Case-3) The length of the preceding HIGH level period of the potential of the input clock signal S(CLK) exceeds 4 cycle periods of the S(REF), and the length of the present LOW level period of the potential of the input clock signal S(CLK) is less than 4 cycle periods of the S(REF). The waveforms of the signals in Case-3 are shown in Fig. 6. In the case of Fig. 6, the preceding HIGH level period t7 exceeds 4 cycle periods of the S(REF), and the present LOW level period t8 is less than 4 cycle periods of the S(REF). The outputs of the shift registers 2l and 22 are as shown in S(2l) and S(22). At the time of the pulse p5, the reversal of the outputs of the flip-flip circuit 3 does not take place, so that the potential of the Q output S(3, Q) is maintained at a HIGH level, and the potential of the Q output S(3, Q ) is maintained at a LOW level. The outputs of the AND gate 4l, the inverter 6l, the AND gate 42, the inverter 62, the AND gate 7l, and the inverter 72 are as shown in S(4l), S(6l), S(42), S(62), S(7l), and S(72). The outputs q5, q6, q7, ... of the OR gate 8l are as shown in S(8l). The pulses q5 and q6 are produced immediately after the rising and the falling of the input clock signal p4, and the pulse q7 is produced immediately after the falling of the input clock signal p5. Accordingly, after the input of the clock signal p5, the frequency of the output signal is not multiplied by the frequency of the input clock signal but is maintained at the same level as the frequency of the input clock signal. (Case-4) Each of the HIGH level period and the LOW level period of the potential of the input clock signal S(CLK) is less than 4 cycle periods of the S(REF). The waveforms of the signals in Case-4 are shown in Fig. 7. In the case of Fig. 7, each of the HIGH level periods t9, tll, tl3, ... and the LOW level periods tl0, tl2, ... is less than 4 cycle periods of the S(REF). In the case of Fig. 7, each of the potentials of the outputs of the shift registers 2l and 22 is maintained at a LOW level. The Q output S(3, Q) of the flip-flop circuit 3 is maintained at a HIGH level, and the Q output S(3, Q ) of the flip-flip circuit 3 is maintained at a LOW level. The outputs of the AND gate 4l, the inverter 6l, the AND gate 42, the inverter 62, the AND gate 7l, and the inverter 72 are as shown in S(4l), S(6l), S(42), S(62), S(7l) and S(72). The outputs q7, q8, q9, ... of the OR gate 8l are as shown in S(8l). The pulses q7, q8, q9, ... are produced only immediately after the falling of the input clock signals p5, p6, p7, ... Accordingly, the frequency of the output signal is not multiplied by the frequency of the input clock signal but is maintained at the same level as the frequency of the input clock signal. The output signal S(8l) of the frequency multiplying circuit of Fig. 3 is used for an input clock signal S(20l) of a data latch circuit shown in Fig. 8 as a data reading circuit. The data latch circuit shown in Fig. 8 includes a circuit 202 for generating double cycle period clock signals ⊘₁ and ⊘₂ , a toggle flip-flop circuit 2l3, a D type flip-flop circuit 2l4, a sequence of three latch elements 2l5, 2l6, and 2l7, and an exclusive OR gate 2l8. The latch circuit shown in Fig. l delivers an output signal S(READ DATA) from the exclusive OR gate 2l8. In the data latch circuit shown in Fig. 8, the double cycle period clock signals ⊘₁ and ⊘₂ delivered from the circuit 202 are supplied to one input terminal of the D type flip-flip circuit 2l4 and the Latch elements 2l5, 2l6, and 2l7.

Claims: A frequency multiplying circuit comprising: a reference input frequency (S(REF)); a first time counting means (21) responsive to input pulse signals for producing a first detection signal when said input pulse signals maintain a HIGH level for a time greater than that required for a predetermined number of periods of the reference input; a second time counting means (22) responsive to the input pulse signals for producing a second detection signal when said input pulse signals maintain a LOW level for a time greater than that required for a predetermined number of periods of the reference input; a pulse generation determining means (3) responsive to said produced first and second detection signals for realizing a SET state by said produced first detection signal and realizing a RESET state by said produced second detection signal to generate gate signals; a first pulse generating means (41,51,61,71) responsive to one of said generated gate signals for detecting rising edges of said input pulse signals to generate first pulses which are substantially synchronous with said rising edges; a second pulse generating means (42,52,62,72) responsive to the other of said generated gate signals for detecting falling edges of said input pulse signals to generate second pulses which are substantially synchronous with said falling edges; said first and second pulses being delivered as frequency multiplied signals of said input pulse signals; whereby the frequency multiplication of said input pulse signals only occurs when the period of said input pulse signals exceeds the time required for a predetermined number of periods of the reference input. A frequency multiplying circuit according to claim 1, wherein said first pulse generating means comprises: a first delay circuit (51) for delaying by a predetermined period a detected signal which is detected according to one of said generated gate signals and the rising edge of a said input pulse signal, and a first output circuit (71) for outputting said first pulse by combining said detected signal and said delayed signal. A frequency multiplying circuit according to claim 1, wherein said second pulse generating means comprises: a second delay circuit (52) for delaying by a predetermined period a detected signal which is detected according to the other of said generated gate signals and the falling edge of a said input pulse signal, and a second output circuit (72) for outputting said second pulse by combining said detected signal and said delayed signal.

Inventors: SATOH, NAKATOSHI
Applicants: FUJITSU LIMITED
Application year: 1987
Main classification: H03M5
IPC codes: H03K5, G11B20, H04L7, H03K6