Pulse modulation signal generation circuit, and semiconductor laser modulation device, optical scanning device and image formation device using the same

• US 6,731,317 B2
• Filed: 03/13/2002
• Issued: 05/04/2004
• Est. Priority Date: 03/14/2001
• Status: Active Grant

• Current Assignee: Ricoh Company Limited
• Original Assignee: Ricoh Company Limited
• Inventors: Ishida, Masaaki, Nihei, Yasuhiro, Ema, Hidetoshi
• Primary Examiner(s): LEE, SUSAN SHUK YIN
• Application Number:
  US10/095,913
• Publication Number:
  US 20020130944A1
• Time in Patent Office: 783 Days
• Field of Search: 347/135, 347/143, 347/144, 347/252, 347/253, 347/132, 347/248
• US Class Current: 347/135
• CPC Class Codes: H04N 1/40037 the reproducing element being a laser
• CPC Class Codes: H04N 1/4056 the pattern varying in one dimension only, e.g. dash length, pulse width modulation [PWM]

Abstract

A clock generating part generates a high-frequency clock signal having a frequency higher than that of a pixel clock frequency; a serial modulation signal generating part generates a serial modulation signal having a serial pulse sequence based on the high-frequency clock signal, and, light emission is modulated according to the serial modulation signal, and, thus, each pixel of an image is formed according at the pixel clock frequency.

Claims

1. A pulse modulation signal generating circuit comprising:

a clock generating part generating a high-frequency clock signal having a frequency higher than that of a pixel clock frequency; and

a serial modulation signal generating part generating a serial modulation signal having a serial pulse sequence based on the high-frequency clock signal,

wherein light emission is modulated according to the serial modulation signal, and, thus, each pixel of an image is formed according to the pixel clock frequency.

2. The pulse modulation signal generating circuit as claimed in claim 1, further comprising a modulation data generating part generating modulation data comprising a predetermined bit pattern according to given image data, said serial modulation signal generating part generating the serial modulation signal based on the modulation data.

3. The pulse modulation signal generating circuit as claimed in claim 2, wherein said modulation data generating part changes a number of bits of the modulation data.

4. The pulse modulation signal generating circuit as claimed in claim 3, wherein said modulation data generating part makes a pulse occurrence rate on the modulation data uniform while changing the number of bits.

5. The pulse modulation signal generating circuit as claimed in claim 3, wherein said modulation data generating part makes a pulse occurrence pattern on the modulation data unchanged while changing the number of bits.

6. The pulse modulation signal generating circuit as claimed in claim 2, wherein said modulation data generating part comprises a look-up table for converting given image data into corresponding modulation data.

7. The pulse modulation signal generating circuit as claimed in claim 6, wherein said look-up table comprises a plurality of look-up tables, and switching is made from among outputs of said plurality of look-up tables to determine one to be used according to the given image data.

8. The pulse modulation signal generating circuit as claimed in claim 7, wherein said plurality of look-up tables have different bit lengths.

9. The pulse modulation signal generating circuit as claimed in claim 7, wherein said plurality of look-up tables comprise two sets thereof, a first one comprising a plurality of look-up tables having different bit lengths, and a second one comprising a plurality of look-up tables corresponding to the configurations of said first one.

10. The pulse modulation signal generating circuit as claimed in claim 2, wherein said modulation data generating part comprises a decoder decoding given image data into corresponding modulation data.

11. The pulse modulation signal generating circuit as claimed in claim 2, wherein said modulation data generating part comprises a look-up table for converting given image data into corresponding modulation data, a decoder decoding given image data into corresponding modulation data, and a selector selecting the output of one of said look-up table and decoder.

12. The pulse modulation signal generating circuit as claimed in claim 1, wherein said serial modulation signal generating part loads the modulation signal according to a given load signal and converts it into a serial pulse sequence according to the high-frequency clock signal.

13. The pulse modulation signal generating circuit as claimed in claim 12, wherein said serial modulation signal generating part comprises a shift register.

14. The pulse modulation signal generating circuit as claimed in claim 12, wherein said serial modulation signal generating part comprises a plurality of shift registers, and a selector selecting one of the outputs of said plurality of shift registers.

15. The pulse modulation signal generating circuit as claimed in claim 14, wherein said plurality of shift registers operate according to a single clock signal having a frequency 1/M that of the high-frequency clock signal, where M denotes a natural number more than 1.

16. The pulse modulation signal generating circuit as claimed in claim 15, wherein said serial modulation signal generating part further comprises a phase adjuster adjusting phases of output pulses of said plurality of shift registers.

17. The pulse modulation signal generating circuit as claimed in claim 14, wherein said plurality of shift registers operate according to a plurality of phase clock signals having a frequency 1/M that of the high-frequency clock signal, where M denotes a natural number more than 1.

18. The pulse modulation signal generating circuit as claimed in claim 1, wherein said clock generating part comprises a PLL comprising a differential-type ring oscillator, wherein the high-frequency clock signal comprises a plurality of clock signals having different phases obtained as a result of a plurality of phases are taken by said ring oscillator.

19. The pulse modulation signal generating circuit as claimed in claim 1, wherein said clock generating part comprises a PLL comprising a delay part delaying a reference clock signal so as to provide a plurality of clock signals having different phases, wherein the high-frequency clock signal comprises said plurality of clock signals having different phases obtained from said delay part.

20. The pulse modulation signal generating circuit as claimed in claim 19, wherein said clock generating part further comprises a control part controlling a delay amount on said delay part.

21. The pulse modulation signal generating circuit as claimed in claim 20, wherein said control part comprises a detection part detecting the delay amount on the clock signal obtained from said delay part, and an error amplifier.

22. A semiconductor laser modulation device comprising:

a semiconductor laser;

a laser modulating part modulating a laser beam emitted from said semiconductor laser according to a pulse modulation signal; and

the pulse modulation signal generating circuit claimed in claim 1 generating the pulse modulation signal to be used by said laser modulating part.

23. An optical scanning device comprising:

a semiconductor laser;

a scanning optical system deflecting a laser beam emitted by said semiconductor laser;

a laser modulating part modulating a laser beam emitted from said semiconductor laser according to a pulse modulation signal; and

the pulse modulation signal generating circuit claimed in claim 1 generating the pulse modulation signal to be used by said laser modulating part.

24. An image formation device comprising:

a semiconductor laser;

a scanning optical system deflecting a laser beam emitted by said semiconductor laser;

an image forming part forming an image according to the laser beam deflected by said scanning optical system;

a laser modulating part modulating a laser beam emitted from said semiconductor laser according to a pulse modulation signal; and

the pulse modulation signal generating circuit claimed in claim 1 generating the pulse modulation signal to be used by said laser modulating part.

25. The image formation device as claimed in claim 24, wherein said semiconductor laser is configured such as to emit a plurality of laser beams simultaneously.

26. An exposure method comprising the steps of:

a) driving a light-emitting unit according to modulation signal; and

b) exposing a photoconductor while scanning it with a laser beam emitted by said light-emitting unit, wherein;

the modulation signal comprises a pulse sequence; and

an exposure energy distribution in which the photoconductor is exposed is determined as a result of control of both a pulse width and a pulse pattern of the pulse sequence.

27. The method as claimed in claim 26, wherein, as a result of control of the exposure energy distribution, a density of a latent image formed on the photoconductor is controlled at each position.

28. The method as claimed in claim 26, wherein as a result of control of the exposure energy distribution, a density of a latent image formed on the photoconductor is controlled on each pixel.

29. The method as claimed in claim 26, wherein the exposure energy distribution is controlled not only by control of total light-emission time interval during each unit time but also by controlled of light-emission timing there.

30. The method as claimed in claim 26, wherein the exposure energy distribution is controlled not only by control of total light-emission time interval for each pixel but also by control of light-emission timing thereof.

31. The method as claimed in claim 26, wherein:

modulation in the modulating signal is made in synchronization with an image clock signal;

a scanning speed on the photoconductor is detected; and

phase of pulses of the image clock signal is controlled according to the thus-detected scanning speed.

32. The method as claimed in claim 31, wherein

a polygon mirror is used for scanning the photoconductor;

the detected scanning speed is stored for each of the number of polygon surfaces of the polygon mirror; and

phase of pulses of the image clock signal is controlled according to the thus-detected scanning speed for each polygon surface.

33. An exposure device comprising:

a part driving a light-emitting unit according to modulation signal; and

a part exposing a photoconductor while scanning it with a laser beam emitted by said light-emitting unit,

wherein;

the modulation signal comprises a pulse sequence; and

an exposure energy distribution in which the photoconductor is exposed is determined as a result of control of both a pulse width and a pulse pattern of the pulse sequence.

34. The exposure device as claimed in claim 33, wherein, as a result of control of the exposure energy distribution, a density of a latent image formed on the photoconductor is controlled at each position.

35. The exposure device as claimed in claim 33, wherein, as a result of control of the exposure energy distribution, a density of a latent image formed on the photoconductor is controlled on each pixel.

36. The exposure device as claimed in claim 33, wherein the exposure energy distribution is controlled not only by control of total light-emission time interval during each unit time but also by control of light-emission timing there.

37. The exposure device as claimed in claim 33, wherein the exposure energy distribution is controlled not only by control of total light-emission time interval for each pixel but also by control of light-emission timing therefor.

38. The exposure device as claimed in claim 33, wherein:

modulation in the modulating signal is made in synchronization with an image clock signal;

a scanning speed on the photoconductor is detected by a detecting part; and

phase of pulses of the image clock signal is controlled according to the thus-detected scanning speed.

39. The exposure device as claimed in claim 38, wherein

a polygon mirror is used for scanning the photoconductor;

the detected scanning speed is stored for each of the number of polygon surfaces of the polygon mirror; and

phase of pulses of the image clock signal is controlled according to the thus-detected scanning speed for each polygon surface.

40. An image formation device, comprising:

a part driving a light-emitting unit according to modulation signal; and

a part exposing a photoconductor while scanning it with a laser beam emitted by said light-emitting unit, so as to form a latent image on the photoconductor,

wherein;

the modulation signal comprises a pulse sequence; and

an exposure energy distribution in which the photoconductor is exposed is determined as a result of control of both a pulse width and a pulse pattern of the pulse sequence.

41. An optical modulation signal generating circuit generating a modulation signal for exposing a photoconductor, comprising:

a part generating a pulse sequence as the modulation signal; and

a part controlling of both a pulse width and a pulse pattern of the pulse sequence so as to control an exposure energy distribution in which the photoconductor is exposed.

42. The optical modulation signal generating circuit as claimed in claim 41, wherein, as a result of control of the exposure energy distribution, a density of a latent image formed on the photoconductor is controlled at each position.

43. The optical modulation signal generating circuit as claimed in claim 41, wherein, as a result of control of the exposure energy distribution, a density of a latent image formed on the photoconductor is controlled on each pixel.

44. The optical modulation signal generating circuit as claimed in claim 41, wherein the exposure energy distribution is controlled not only by control of total light-emission time interval during each unit time but also by control of light-emission timing there.

45. The optical modulation signal generating circuit as claimed in claim 41, wherein the exposure energy distribution is controlled not only by control of total light-emission time interval for each pixel but also by control of light-emission timing therefor.

46. The optical modulation signal generating circuit as claimed in claim 41, wherein:

modulation in the modulating signal is made in synchronization with an image clock signal;

a scanning speed on the photoconductor is detected by a detecting part; and

phase of pulses of the image clock signal is controlled according to the thus-detected scanning speed.

47. The optical modulation signal generating circuit as claimed in claim 46, wherein:

a polygon mirror is used for scanning the photoconductor;

the detected scanning speed is stored for each of the number of polygon surfaces of the polygon mirror; and

phase of pulses of the image clock signal is controlled according to the thus-detected scanning speed for each polygon surface.