JPH0219080A - Semiconductor photodetector - Google Patents

Abstract

PURPOSE:To obtain an accurate signal output by constituting the photodetector by a circuit discharging the photodetector till a reference potential in time series after the photoelectric conversion of all the photodetectors is finished. CONSTITUTION:A transistor(TR) DTn discharges each photodetector 1 to a reference potential, a transmission gate TGn receives a signal of a shift register SRn, is in sequential conduction and outputs a signal of each photodetector. Then the TR DTn is driven after the signal of all the photodetectors is finished. Thus, the timing driving the transmission gate TGn outputting a signal of the photodetector 1 and driving the TR DTn discharging the photodetector 1 to a reference voltage are deviated and the noise component caused in the signal output is reduced. Thus, the read signal for an original or drawing or the like is outputted with high accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor light-receiving device that can receive reflected light from a document irradiated with light and convert it into an electrical signal.

[Summary of the Invention] The present invention comprises a circuit driven by a discharge circuit that resets all photoelectric conversion light receiving elements (hereinafter referred to as light receiving elements) to a reference potential after completing photoelectric conversion. It is a semiconductor photodetector. Therefore, noise components are not added to the signal output during photoelectric conversion, making it possible to accurately obtain the signal output.

Furthermore, since the discharge circuit can be driven by the shift register constituting the reading circuit, the present invention can be implemented by simply adding a simple circuit.

(Prior Art) Conventionally, as shown in Fig. 3, a semiconductor light receiving device is equipped with a light receiving element, a reading circuit that converts the electric signal obtained by the light receiving element in time series, and a discharging circuit that discharges the light receiving element to a reference voltage. was configured.

[Problems to be Solved by the Invention] However, in the case of the circuit configuration shown in Fig. 3, when all the circuits are created as an integrated circuit on the same semiconductor substrate, after the metal wiring is formed, SiOx etc. Since the entire surface is covered with an insulating film, an equivalent circuit is formed in which capacitors C1 and C1 are connected between the output terminal of the light-receiving element 1 and a wiring that applies a gate voltage for driving a discharge transistor. In addition, the state transition diagram of the circuit of FIG. 3 is shown in FIG. 4. Note that the signal SI is input to the shift register data input signal terminal,
A signal SO is output from the shift register data output terminal, a control signal INH is input to the control signal input terminal, and a video signal SIG is output from the video signal output terminal. Signals DT1', DT2',
DT3', . . . DT(n-1)' and DTn' are respectively switching transistors DT1. DT2, DT
3. Applied to the gates of DT(n-1) and DTn.

Also, the signals TGI', TG2', TG3',...T
G(n-1)' and TGn' are transmission gates TGI, TG2, TG3,...TG(n-1), respectively.
) and the gate of the transistor on the N-channel side of TGn. Due to the equivalent circuit in which the capacitors C1 and C1 are connected, the switching transistor DTI turns 0FFL and the switching transistor DT2 turns ON at the time when the light receiving element 1 outputs a signal, that is, at the timing when the transmission gate 1-TG3 turns ON. Since the noise component is added to the signal output of the light receiving element 1 via the capacitor CC2, it is impossible to accurately measure the signal output. Also, at the timing when transmission gate TG3 turns on,
Including the shift registers SR1, .

Furthermore, at the timing when the transmixing gate TG3 turns on, the switching transistor DTI turns 0FF.
L, switching transistor DT2 is turned on.

However, at the timing when the transmission gate TG1 turns on, none of the discharge transistors is driven, and at the timing when the transmission gate TG2 turns on, the switching transistor DTI turns on.
6, that is, transmission gate T
The noise components added to the signal output of each light receiving element differ at the timing when GI, TG2, and TG3 turn on.
Variations occur between signal outputs. This is 1. This is particularly noticeable in the dark output state because the signal output is at a low voltage.

[Means to solve the problem]

In order to solve the above problems, the present invention includes a circuit that discharges the light receiving elements in time series to a reference potential after the photoelectric conversion of all the light receiving elements is completed. That is, as shown in the state transition diagram of FIG. 2, the discharge transistor is not driven during the period when the light receiving element is outputting, and after the photoelectric conversion of all the light receiving elements is completed, the discharge transistor is turned ON one after another.
During photoelectric conversion, the discharge transistor is
It is in an FF state, no noise component is added to the signal output, and the circuits driven at the timing when each transmission gate turns on are all the same.

[Example] Examples of the present invention will be described in detail below based on the drawings.

FIG. 1 is an equivalent circuit diagram of a semiconductor light receiving device of the present invention. FIG. 2 is a state transition diagram of the semiconductor light receiving device of the present invention. In FIG. 2, for example, a signal input to transmission gate TGI is indicated by TGl'. In FIG. 1, the transistor TGn discharges each light receiving element to a reference potential. The transmission gate TGn receives a signal from the shift register SRn, sequentially becomes conductive, and outputs a signal from each light receiving element. The transistor DGn is driven only after the signals from all the light receiving elements have finished outputting. For this purpose, as shown in FIG. 1, transmission gate TG3 and switching transistors DGl and DG2 are
Even if capacitances C1 and C8 exist between the transmission gates TG3 and TG3, noise components are added to the transmission gate TG3 after the light-receiving element signal is output, so this is not a problem. Since all driving circuits are the same, there is no variation in signal output.

Further, in order to carry out the present invention, the circuit used does not require a special circuit and can be easily configured. In Figure 1, the shift register is initially driven to sequentially output the light receiving elements, and is also used primarily to drive the discharge transistor, resulting in a circuit configuration that reduces the number of elements. The third aspect of the present invention is to reduce noise components added when a signal from a light receiving element is output, and it is obvious that it can be implemented with a circuit configuration other than that shown in FIG.

The semiconductor light receiving device of the present invention is formed by the circuit described above, and it is possible to detect a clear signal without adding noise components to the photoelectrically converted signal output.

[Effects of the Invention] As explained above, the present invention is composed of a simple circuit, and controls the timing of driving the transmission gate that outputs the signal of the light receiving element and the transistor that discharges the light receiving element to a reference voltage. This has the effect of reducing noise components generated in the signal output. Like this,
The present invention has the effect of providing an inexpensive semiconductor light receiving device in which signals from a device for reading manuscripts, drawings, etc. can be output with high precision.

[Brief explanation of the drawing]

FIG. 1 is an equivalent circuit diagram of the semiconductor photodetector of the present invention, and FIG.
The figure shows a timing chart of a semiconductor light receiving device of the present invention;
FIG. 3 is an equivalent circuit diagram of a conventional semiconductor light receiving device, and FIG. 4 is a timing chart of the conventional semiconductor light receiving device. l... Light receiving element t,... TGI ON timing t,... TG
Timing t when TG 2 turns on,...Temperature when TG3 turns on

Claims (1)

[Claims] A semiconductor device including a plurality of photoelectric conversion elements, a reading circuit that sequentially reads output signals of the photoelectric conversion element, and a discharge circuit that resets the photoelectric conversion element to a reference potential, the reading circuit including a plurality of photoelectric conversion elements. A semiconductor light-receiving device characterized in that the discharge circuit is driven after all output signals of the conversion element are read out.