Voltage controlled oscillator, PLL circuit, pulse modulation signal generating circuit, semiconductor laser modulation device and image forming apparatus

• US 7,193,480 B2
• Filed: 05/27/2004
• Issued: 03/20/2007
• Est. Priority Date: 05/30/2003
• Status: Expired due to Fees

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Ishida, Masaaki, Nihei, Yasuhiro, Omori, Atsufumi, Ozasa, Dan
• Primary Examiner(s): Shingleton; Michael B
• Application Number:
  US10/854,268
• Publication Number:
  US 20040251973A1
• Time in Patent Office: 1,027 Days
• Field of Search: 331/57, 331/175, 331/16, 331/185
• US Class Current: 331/57
• CPC Class Codes: H03K 3/0315 Ring oscillators
• CPC Class Codes: H03K 3/0322 with differential cells
• CPC Class Codes: H03L 7/0816 the controlled phase shifter and the frequency- or phase-detection arrangement being connected to a common input
• CPC Class Codes: H03L 7/0891 the up-down pulses controlling source and sink current generators, e.g. a charge pump
• CPC Class Codes: H03L 7/0995 the oscillator comprising a ring oscillator
• CPC Class Codes: H03L 7/18 using a frequency divider or counter in the loop H03L7/20, H03L7/22 take precedence

Abstract

An oscillation frequency control part includes a voltage-to-current converting circuit converting an input voltage to a current having a value corresponding to the input voltage, and outputting a current in proportion to the current obtained from the voltage-to-current converting circuit. An oscillating circuit part includes a ring oscillator, wherein a current in proportion to the output current of the oscillation frequency control part flows through the ring oscillator so that the oscillation frequency in the ring oscillator is controlled by the output current of the oscillation frequency control part. The voltage-to-current converting circuit has linear voltage-to-current conversion characteristics in a predetermined range of the input voltage including a ground potential.

Claims

1. A voltage controlled oscillator comprising:

an oscillation frequency control part comprising a voltage-to-current converting circuit converting an input voltage to a current having a value corresponding to the input voltage, and outputting a current in proportion to the current obtained from said voltage-to-current converting circuit; and

an oscillating circuit part comprising a ring oscillator, wherein a current in proportion to the output current of said oscillation frequency control part flows through said ring oscillator so that the oscillation frequency in said ring oscillator is controlled by the output current of said oscillation frequency control part,

wherein a first power source voltage of said oscillation frequency control part is higher than a second power source voltage of said oscillating circuit part and the oscillation off the oscillating circuit part is carried out between a ground electric potential and the second power source voltage.

2. An image forming apparatus configured to scan a photosensitive body with one or a plurality of laser beams and to form an electrostatic latent image on said photosensitive body, comprising:

a pulse modulation signal generating circuit converting modulation data for modulating said semiconductor laser into a serial pulse series; and

a driving part driving said semiconductor laser according to the serial pulse series output from said pulse modulation signal generating circuit, said pulse modulation signal generating circuit including,

a high-frequency clock generating part generating a high-frequency clock signal from a PLL circuit, and

a serial modulation signal generating part comprising a shift register, providing modulation data having a plurality of bits to the shift register, causing the shift register to perform shift operation according to the high-frequency clock signal so as to convert the modulation data into a serial pulse series to be output,

wherein said PLL circuit comprises;

a voltage controlled oscillator generating a clock signal;

a phase comparing part detecting a phase difference between the clock frequency generated by said voltage controlled oscillator or a frequency obtained from dividing the once oscillated frequency and a reference clock frequency; and

a voltage inputting part inputting a voltage corresponding to the phase difference detected by said phase comparing part to said voltage controlled oscillator,

wherein said voltage controlled oscillator comprises,

an oscillation frequency control part comprising a voltage-to-current converting circuit converting an input voltage to a current having a value corresponding to the input voltage, and outputting a current in proportion to the current obtained from said voltage-to-current converting circuit, and

an oscillating circuit part comprising a ring oscillator,

wherein a current in proportion to the output current of said oscillation frequency control part flows through said ring oscillator so that the oscillation frequency in said ring oscillator is controlled by the output current of said oscillation frequency control part,

wherein the oscillation off the oscillating circuit part is carried out between a ground electric potential and a power source voltage applied to the oscillating circuit, and

wherein said voltage-to-current converting circuit has linear voltage-to-current conversion characteristics in a predetermined range of the input voltage including a ground potential.