Apparatus for reproducing a digital signal

Claim 2

Apparatus for reproducing a digital signal, the apparatus comprising: a phase locked loop circuit (5) to be supplied with a reproduced signal and for generating a clock signal; and a detecting means (10 to 12) for detecting the level of said reproduced signal; characterised by: a control means (13, 14) for controlling a feedback loop of said phase locked loop circuit (5) in response to an output signal of said detecting means (10 to 12).

Claim 3

Apparatus according to claim 1 wherein said phase locked loop circuit (5) comprises an oscillator means (9) which has an oscillation frequency which is varied by a control signal, a phase comparing means (6) for phase- comparing said reproduced signal and an output from said oscillator means (9), a charge pump circuit (7) connected to an output of said phase comparing means (6), and a low-pass first filter (8) connected to said charge pump circuit (7) for generating said control signal, and said control means (10 to 12) controls the operation of said charge pump circuit (7) in response to the output of said detecting means (10 to 12).

Claim 4

Apparatus according to .claim 2 wherein said low-pass first filter means (8) includes an amplifier (41) of an integration type.

Claim 5

Apparatus according to claim 1 wherein said detecting means (10 to 12) comprises an envelope detecting means (10) for detecting an envelope of said reproduced signal, a comparator means (11) connected to an output of said envelope detecting means (10), and a second filter (12) connected to said comparator means (11) for removing noise.

Claim 6

Apparatus according to claim 2 further comprising a variable waveform equalization means (3) which is supplied with said reproduced signal and supplies an output signal to said phase locked loop circuit (5), the frequency characteristic of said variable waveform equalization thereof being varied by said control signal.

Claim 7

Apparatus according to claim 2 further comprising a rotary head means (1) for reproducing a digital signal recorded on a tape and generating said reproduced signal, a motor (19) for driving said rotary head means (1) so that it rotates, and a motor driving means,(18) for controlling the rotation of said motor (19) with said control signal such that when said tape is transported at high speed, the relative speed between said tape and said rotary head means (1) is equal to the relative speed during the normal playback mode.

Claim 8

Apparatus for reproducing digital signals from magnetic tape, the apparatus comprising: a rotary head (1) for reproducing digital data from said tape; a motor (19) for driving said rotary head (1) ; a motor drive means (18) for supplying an output to said motor (19); a switch means (17) connected to said motor drive means (18) and in a first position supplying a normal speed signal thereto and in a second position supplying a high speed signal thereto; a comparing circuit (15) connected to said switch means (17) to supply said high speed signal; - a-phase locked loop circuit (5) for receiving an output signal from said rotary head (1) and including a voltage controlled oscillator (9) and a phase comparing/data extracting circuit (6) which receives an input from said voltage controlled oscillator (9); a charge pump circuit (7) connected to receive the output of said phase comparing/data extracting circuit (6); a first low-pass filter (8) for receiving the output of said charge pump circuit (7) and for supplying an input to said voltage controlled oscillator (9); and a second low-pass filter (13) for receiving the output of said first low-pass filter and supplying an input to said comparing circuit (15).

Claim 9

Apparatus for reproducing digital signals from magnetic tape, the apparatus comprising: a rotary head (1) for reproducing digital data from said tape; a motor (19) for driving said rotary head (1) ; a motor drive means (18) for supplying an output to said motor (19); a switch means (17) connected to said motor drive means (18) and in a first position supplying a normal speed signal thereto and in a second position supplying a high speed signal thereto; a comparing circuit (15) connected to said switch means (17) to supply said high speed signal; - a-phase locked loop circuit (5) for receiving an output signal from said rotary head (1) and including a voltage controlled oscillator (9) and a phase comparing/data extracting circuit (6) which receives an input from said voltage controlled oscillator (9); a charge pump circuit (7) connected to receive the output of said phase comparing/data extracting circuit (6); a first low-pass filter (8) for receiving the output of said charge pump circuit (7) and for supplying an input to said voltage controlled oscillator (9); and a second low-pass filter (13) for receiving the output of said first low-pass filter and supplying an input to said comparing circuit (15).

Claim 10

Apparatus according to claim 7 including a variable waveform equalzation means (3) and a wave shaping means (4) connected between said rotary head (1) and said phase comparing/data extracting circuit (6), and a control signal generating means (14) for receiving the output of said second low-pass filter (13) and supplying an input to said variable waveform equalization means (3).

Claim 11

Apparatus according to claim 8 including a high speed envelope detecting means (10) for receiving the output of said rotary head (1), a tracking comparator (11) for receiving the output of said high speed envelope detecting means (10), and a random walk filter (12) for receiving the output of said tracking comparator means (11) and an output from said voltage controlled oscillator (9) and for supplying an input to said charge pump circuit (7).