JPH0670239A - Solid state image pickup device - Google Patents

Abstract

PURPOSE:To provide a solid state image pickup device which contains an output amplifier that can vary the gate potential of a load transistor TR. CONSTITUTION:The signal charge generated by the signal light which is made incident on a photodiode 1 that performs the photoelectric transformation on a semiconductor substrate is transferred by a vertical CCD 2 and a horizontal CCD 3. An output amplifier detects the transferred signal charge as a voltage charge component of the signal detecting capacity provided on the semiconductor substrate and then outputs the signal voltage in accordance with the detected voltage change component. Then the driving power generating circuits are provided to the TR 20-23 which construct the output amplifier.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a solid-state image pickup device using a charge transfer device.

[0002]

2. Description of the Related Art A solid-state image pickup device using a charge transfer device represented by a charge-coupled device (CCD) has recently been put into practical use due to its superiority in low noise characteristics.

A conventional solid-state image pickup device will be described below with reference to the drawings. FIG. 2 shows a circuit configuration diagram of a conventional solid-state imaging device. The photodiodes 1 arranged two-dimensionally are connected to the vertical CCDs 2 for each column. Further, the vertical CCD 2 is connected to the horizontal CCD 3. The horizontal CCD 3 is connected to the output amplifier via the charge detection capacitor 5. The output amplifier is composed of a two-stage source follower circuit including a driver transistor 6, a load transistor 7, a driver transistor 8, and a load transistor 9. Further, the transistors 10 and 11 are voltage generating circuits and are connected to the gates of the load transistors 7 and 9 of the output amplifier.

Signal charges generated by photoelectric conversion in the photodiode 1 are transferred to the vertical CCD 2 and the horizontal CCD 3,
The voltage is converted by the charge detection capacitor 5 and input to the gate of the driver transistor 6 of the output amplifier. Then, a signal voltage corresponding to the input voltage is output from the output terminal 15 of the two-stage source follower circuit. The transistor 4 is a reset transistor for resetting the charge detection capacitor 5, the terminal 12 is a control terminal of the reset transistor 4,
The terminal 13 is a terminal that applies a reset potential.

In the solid-state image pickup device configured as described above, the output amplifier is an important constituent element that influences the characteristics of the entire solid-state image pickup device.

[0006]

The characteristics of the output amplifier are
It can be controlled by the size of the transistors 6, 7, 8 and 9 forming the output amplifier and the impurity concentration of the semiconductor substrate.
However, for the simplest and surest control, the gate potentials of the load transistors 7 and 9 should be controlled.
In the above-described conventional solid-state imaging device, the gate potential is uniquely determined by the output voltage of the circuit including the transistors 10 and 11, and in particular, the gate potential cannot be changed after the solid-state imaging device is manufactured. There were challenges.

There is also an example in which an input terminal is provided so as to supply the gate potentials of the load transistors 7 and 9 from the outside of the solid-state image pickup device, but since the number of power supplies for driving the device is increased, each device is There was a problem that it was necessary to adjust the voltage value every time.

Therefore, an object of the present invention is to provide a solid-state image pickup device having an output amplifier whose gate potential of a load transistor is variable.

[0009]

In order to solve the above problems, the present invention transfers a photoelectric conversion means formed on a semiconductor substrate and a signal charge generated by signal light incident on the photoelectric conversion means. Of the signal charge transfer means and the signal charge carried by the signal charge transfer means are detected as a voltage change amount of the signal detection capacitance provided on the semiconductor substrate, and a signal voltage corresponding to the voltage change amount is output. An output amplifier is provided, and a plurality of power supply generation circuits for driving the transistors forming the output amplifier are provided.

[0010]

According to the above construction, the most suitable value among the plurality of load transistor gate potentials can be easily set.

[0011]

1 is a diagram showing the configuration of a solid-state image pickup device according to an embodiment of the present invention. In the figure, the same reference numerals as those in FIG. 2 showing the conventional example indicate the same things. The difference from the conventional circuit is that the voltage generation circuit includes two circuits, a voltage generation circuit composed of transistors 20 and 21, and a voltage generation circuit composed of transistors 22 and 23, and the output of each circuit is the load of the output amplifier. That is, it is connected to the gates of the transistors 7 and 9.

In general, the characteristics of a MOS transistor are greatly influenced by the drain current, and the design of this current value is the basis of circuit design. Therefore, in the output amplifier of the solid-state imaging device, the load transistors 7 and 9 cause the driver transistors 6 and 8 to operate as constant current sources.
As a result, the drain currents of the driver transistors 6 and 8 are kept constant and stable operation becomes possible. Also,
Since the voltage between the gate and the source controls the drain current of the MOS transistor, the gate potential of the load transistor is a major factor that determines the characteristics of the output amplifier. That is, the solid-state imaging device of this embodiment includes a plurality of voltage generating circuits, and the output of each voltage generating circuit is connected to the gate of the load transistor of the output amplifier.

In other words, the signal charge generated by the signal light incident on the photodiode 1 for photoelectrically converting on the semiconductor substrate is transferred by the vertical CCD 2 and the horizontal CCD 3, and this signal charge is transferred to the signal provided on the semiconductor substrate. It is composed of an output amplifier that detects the voltage change of the detection capacitance and outputs a signal voltage corresponding to the voltage change. In addition, the transistor 20 which constitutes this output amplifier
23 to 23 are provided. The output amplifier is composed of a source follower circuit, and the outputs of the driving power supply generation circuits of the transistors 20 to 23 are connected to the gate electrodes of the load transistors 7 and 9 of the source follower circuit.

Specifically, when the gate potential of the load transistor is increased, the gain of the output amplifier is decreased, the high cutoff frequency is increased, and the power consumption is increased.

Transistor 2 which constitutes a voltage generating circuit
The gate length and the gate width of 0 and 21 are L ₂₀ , W ₂₀ , and
Assuming that L ₂₁ and W ₂₁ , the voltage V _LG supplied to the gates of the load transistors 7 and 9 is given by the following equation, with the voltage supplied to the terminal 14 being V _OD .

V _LG = V _OD / (1 + k) -V _T · (1-k) / (1 + k) where k = (L ₂₀ · W ₂₁ / L ₂₁ · W ₂₀ ) ^1/2 V _T : Threshold Value voltage In this way, a desired voltage can be easily designed from the gate sizes of the two transistors 20 and 21. In this embodiment, this voltage generating circuit has two different gate sizes.
A circuit is provided.

By adjusting the output amplifier characteristics when the signal charge amount transferred from the photodiode deviates from the design value due to variations in the manufacturing process or when it is desired to simultaneously manufacture solid-state image pickup devices having different characteristics. There are many things we can handle. For example, when the same solid-state imaging device is required to reduce power consumption, to increase the cutoff frequency, or to increase the output voltage for the purpose of use, the output amplifier characteristic can be used.

For example, if the output voltage of the voltage generating circuits 22 and 23 is set to be 10% lower than the output voltage of the voltage generating circuits 20 and 21, the voltage generating circuits 22 and 23 are set.
Is selected, the drain currents of the load transistors 7 and 9 of the output amplifier are reduced by about 20%, the cutoff frequency is reduced by about 20%, and the gain of the output amplifier is reduced compared to the case where the voltage generation circuits 20 and 21 are selected. The output voltage of the solid-state imaging device also increases by about 10%.

The selection of the voltage generating circuit is performed by selecting, for example, the circuit 20,
The wiring 31 may be cut when selecting 21 and the wiring 30 may be cut by using a laser trimmer or the like when selecting the circuits 22 and 23. This can be done after manufacturing the solid-state imaging device while confirming the characteristics, which is simple and reliable.

Although an example in which two voltage generating circuits are provided has been described above, it is clear that more detailed measures can be taken by increasing the number of these circuits.

[0021]

As described above, according to the solid-state image pickup device of the present invention, even after the solid-state image pickup device is manufactured, a circuit for providing a plurality of voltage generating circuits and generating the most suitable voltage value is provided. It can be easily selected.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of a solid-state imaging device that is an embodiment of the present invention.

FIG. 2 is a circuit diagram showing a configuration of a conventional solid-state imaging device.

[Explanation of symbols]

 6 Driver Transistor 7 Load Transistor 8 Driver Transistor 9 Load Transistor 20-23 Voltage Generation Circuit Transistor 30, 31 Wiring

Claims (2)

[Claims] 1. A photoelectric conversion means formed on a semiconductor substrate,
The signal charge transfer means for transferring the signal charge generated by the signal light incident on the photoelectric conversion means, and the signal charge carried by the signal charge transfer means are stored in the signal detection capacitor provided on the semiconductor substrate. Detected as a voltage change,
A solid-state imaging device comprising: an output amplifier that outputs a signal voltage according to the voltage change amount; and a plurality of power supply generation circuits for driving the transistors that form the output amplifier. 2. The output amplifier is composed of a source follower circuit, and the output of the transistor driving power supply generation circuit is connected to the gate electrode of the load transistor of the source follower circuit. Solid-state imaging device.