Image reading apparatus and image forming apparatus

An image reading apparatus that converts light reflected from an original into an analog image signal by a photoelectric conversion element, that converts the obtained analog image signal, to which analog signal processing is applied, into a digital image signal by an analog-digital converter, and that outputs the digital image signal, the image reading apparatus comprising:

• a driving unit that drives the photoelectric conversion element by a clock whose frequency is modulated;
• a signal generating unit that generates an analog signal corresponding to a frequency change of the clock whose frequency is modulated;
• an amplification inversion unit that is capable of amplifying an alternating current component of the analog signal with an amplification factor by a setting value that is set from outside, and that is capable of switching the alternating current component between inversion and non-inversion;
• a signal superimposing unit that superimposes the analog image signal on an analog signal that is output from the amplification inversion unit;
• and
• a controlling unit that converts analog image signal that is superimposed by the signal superimposing unit into a digital image signal by using the analog-digital converter, and that controls the amplification factor and the inversion and non-inversion of the amplification inversion unit based on a feature amount that appears on the digital image signal,
• wherein the driving unit includes a phase locked loop (PLL) circuit for feeding a reference clock whose frequency is modulated,
• wherein the signal generating unit generates an analog signal corresponding to a frequency change of the reference clock by performing a frequency-voltage conversion on a clock signal output from the PLL circuit, and
• wherein the frequency-voltage conversion is performed by a circuit for smoothing the clock signal output from the PLL circuit.

An image reading apparatus that converts light reflected from an original into an analog image signal by a photoelectric conversion element, that converts the obtained analog image signal, to which analog signal processing is applied, into a digital image signal by an analog-digital converter, and that outputs the digital image signal,

• the image reading apparatus comprising:
• means for driving the photoelectric conversion element by a clock whose frequency is modulated;
• means for generating an analog signal corresponding to a frequency change of the clock whose frequency is modulated;
• means for amplification inversion that is capable of amplifying an alternating current component of the analog signal with an amplification factor by a setting value that is set from outside, and that is capable of switching the alternating current component between inversion and non-inversion;
• means for signal superimposing the analog image signal on an analog signal that is output from the means for amplification inversion;
• and
• means for controlling that converts analog image signal that is superimposed by the means for signal superimposing into a digital image signal by using the analog-digital converter, and that controls the amplification factor and the inversion and non-inversion of the means for amplification inversion based on a feature amount that appears on the digital image signal,
• wherein the means for controlling uses a detection value of a peak-bottom difference of the digital image signal in a predetermined image area as the feature amount.