JPS61187367A - Output circuit of charge coupled device - Google Patents

Abstract

PURPOSE:To obtain an output circuit in which electric current flowing in a follower circuit is small and the zero level period of the output voltage and signal period are long, by a method wherein a source follower circuit using P channel MOSFET is connected to an output circuit of a charge coupled device which is an N-type transmitting channel. CONSTITUTION:A floating connecting type detecting circuit is made by providing a source follower circuit 107 using a P channel MOSFET in the output circuit of the charge coupled device which is the N-type transmitting channel. Drain voltage VD is applied through the intermediary of a load resistor 110 to a drain 108 of this P channel MOSFET, and a source 109 is grounded, and an output terminal 111 is taken out from between the resistor 110 and the drain 108. A signal load under the last stage transmitting electrode 101, is transmitted in a floating diffusion area 103 through an output gate 102 when applying voltage VP3 becomes large, and increased load at this rate is accumulated. Accordingly, electric potential of the area 103 is determined by the electric static capacity C, signal load volume Q, and reset level VR, and the relation of Vd= VR-Q/C is established.

Description

[Detailed description of the invention] [Technical field of invention] The present invention relates to an output circuit for a charge coupled device.

[Technical background of the invention and its problems]

A floating junction detection circuit is known as one of the output circuits that converts charge, which is a signal from a charge-coupled device, into voltage and detects it. This is because the signal charge (Q) is the depletion layer capacitance of the pn junction and the capacitance (C
), which causes a potential change in Q/C, and further obtains this potential change as the output voltage of the source follower circuit.

FIG. 5 is a block diagram of a conventional 70-Ting junction type detection circuit. An output voltage (vO
) is provided, and an n-channel MO8FET is provided next to it. In the channel MO8FET, the floating diffusion region (503) corresponding to the source region is connected to the north follower circuit (507).
) of the n-channel MO8FET (504), a reset drain voltage (vBD) is applied to the drain (506), and a reset voltage (VB2') having a pulse waveform is applied to the gate (505).

In the source follower circuit (507), an n-channel MO8FI
The drain voltage (VD) is applied to the drain (508) of the 3T, and the source (509) is grounded via the load resistor (510).The output terminal (511) is connected between the source (509) and the load resistor (510). take. This is an output circuit that converts the potential of the floating diffusion region (503), which changes depending on the amount of signal charge transferred, into an output voltage by a source follower circuit (507) using an n-channel MO8FET.

However, in such a conventional output circuit, when the load resistance (510) of the source follower circuit (507) is increased in order to reduce power consumption, the following problems occur.

Figure 6 shows the voltage applied to the final stage transfer electrode (Vp3), the voltage applied to the reset gate (VB2), the output voltage when the load resistance of the source follower circuit is small (Vou is human), and the output voltage when it is large (vout B). ) shows the relationship between voltage waveforms.

floating diffusion region (503) and reset voltage)
(505) is capacitively coupled and reset gate (50
7 when the reset voltage (va s ) is applied to
A voltage is also applied to the 0-ting diffusion region (503) and reset noise (61') is generated in the output voltage. Rise of reset noise (61) (At, A2, As)
At this time, the n-channel MO8IT is turned on and the drain voltage (VD) is output from the output terminal (511). Falling edge of reset noise (61) (Bl, B2.
B3. B4, 85) to I/Ni Te, n channel MO8F
ET is in the OFF state, and the charges accumulated in the stray capacitance of the source (509) and output terminal (511) are transferred to the load resistance (
510) to the ground potential, the load resistance (5
10), the fall of the output voltage becomes gradual because the time required for the voltage to drop to the reset level is used. Therefore, as can be seen from FIG. 6, when the load resistance (510) of the source follower circuit (507) is large, the output voltage (Vout
B) Zero level period at K (TzatB, Tzsz
B) and the signal period (T561B, T862B) are the zero level period (T26□ person, Tz62 person) and the signal period (Tss 1 person, Ts s 2A) at the output voltage (Vout person) when the load resistance (510) is small. It is shorter in comparison.

The output voltage (VoutB) has a zero level period (Tzs
xB.

If the signal period (TzszB) and signal period (T$61B, T862B) are short, signal processing in the subsequent stage becomes difficult and the signal power also decreases. Therefore, the characteristics of the output circuit of the charge-coupled device deteriorate.

[Purpose of the invention]

An object of the present invention is to provide a floating junction detection circuit for a charge coupled device in which the current flowing through the source follower circuit is small and the zero level period and signal period of the output voltage are long. An output gate provided next to the final stage transfer electrode of the coupling element, a floating diffusion region that transfers and accumulates signal charges existing under the final stage transfer electrode via a barrier under the output gate, and a voltage In the output circuit of a charge transfer device, which consists of a drain region that becomes conductive through a channel under a reset gate to which a voltage is applied, and a source follower circuit using a MOSFET whose gate is connected to a floating diffusion region, Provided is an output circuit for a charge-coupled device characterized by having a source follower circuit using a MOSFET having a conductivity type opposite to that of the channel.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of a floating junction type detection circuit according to an embodiment of the present invention. The drain (107) of an op-channel MO8FFfT is characterized in that a source follower circuit (107) using a p-channel MO8FET is provided in the output circuit of a charge-coupled device that is an image transfer channel.
8) is connected to the drain voltage (V
The 0 source (109) that applies D) is grounded. The output terminal (111) is connected to the load resistor (110) and the drain (108).
).

The signal charges that are sequentially transferred and exist under the final stage transfer electrode (101) are transferred into the floating diffusion region (103) via the output gate (102) when the applied voltage (Vp3) becomes L. Floating diffusion region (103) and pn junction depletion layer capacitance in the semiconductor below and MOSF
The total capacitance consisting of the capacitance of (104) and the capacitance between the output gate (102) and reset gate (105) is increased by the amount of signal charge transferred. is accumulated.

Therefore, the potential (V
d) is determined by the capacitance (C) in this region, the amount of signal charge (Q) flowing into this region, and the reset level (VB) in this region1, Vd = VR-Q/
The relationship C holds true. In addition, the reset gate (105)
When the applied voltage (VR8) becomes H, the signal charges transferred into the bloating region (103) are transferred to the drain region (103).
106). Potential CVd of the 70-ting expansion region (103) that changes depending on the amount of signal charge transferred
) 'r: The output voltage (vout) is converted to K by a source follower circuit (107) using a p-channel MO8FET.

2 and 3 show the p-channel M of the source follower circuit.
A cross-sectional view of an output circuit device of a charge transfer element including an O8FET is shown. Actual devices include the device shown in Figure 2, in which a p-type well is formed in an n-type semiconductor substrate, and a charge transfer element is formed within this region, and the device shown in In the output circuit shown in FIG. 1, an n-type well is formed in a type semiconductor substrate, and an element forming a p-channel MO8FET of a source follower circuit is located in this region.
The relationship between the applied voltage (Vp3) of the final stage transfer electrode (101), the applied voltage (V, , ) of the reset gate (105), and the voltage waveform of the output voltage (vout) is shown. The 70-ting enemy expansion region (103) and the reset gate (105) are capacitively coupled, and when a reset voltage (V, ) is applied to the reset gate (105), the floating diffusion region (
103) is also applied, and reset noise αD is generated in the output voltage. Rise of reset noise (goods) (Cx
, C2, C3), the p-channel MO8FET, which is of the opposite conductivity type to the transfer channel of the charge-coupled device, is in the OFF state. The rise and fall of set noise I (DI, D2, D3, D4
, D5), the p-channel Mo5i'g'r, which is of the conductivity type opposite to the transfer channel of the charge-coupled device, is turned on and rapidly drops to the reset level.

Therefore, in order to reduce power consumption, the load resistance (110)
Even if the output voltage is increased, the zero level period (Tz4
1. Tz42) and signal period (Ts4t #TS42)
does not become shorter, signal processing at the subsequent stage is easier to perform, and the power of the signal becomes larger.

Note that the present invention is not limited to the embodiments described above, and may be modified without departing from the spirit thereof. For example, the conductivity type of the semiconductor substrate may be reversed.Also, since the source follower circuit is the most basic circuit, other circuit designs are possible using MOSFETs with channels of conductivity type opposite to the charge transfer channel. According to the present invention, by using a source follower circuit using an MO81Tt channel having a conductivity type opposite to that of a charge-coupled device channel, a charge-coupled device with low power consumption and a long output voltage zero level period and long signal period can be realized. A floating junction type detection circuit can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an output circuit of a charge coupled device showing an embodiment of the present invention, and FIGS. 2 and 3 are output circuits of a charge coupled device including a MOSFET of a source follower circuit showing an embodiment of the present invention. 4 is a voltage waveform diagram showing the relationship between the voltage (Vp3) s reset voltage (vRs) and the output voltage (vOLlt) applied to the final stage transfer electrode in one embodiment of the present invention, and FIG. 5 6 is a configuration diagram of an output circuit of a charge-coupled device showing a conventional example, and FIG. 6 shows a voltage (vp3) applied to the final stage transfer electrode in a conventional example.
It is a voltage waveform showing the relationship with out2). 101.501...Final stage transfer electrode, 102, 502
...output gate, 103.503..., floating diffusion region,
104.504... Source follower circuit MOSFET
gate, 105.505...reset gate, 10
6.506...Drain, 107.507...Source follower circuit, 108.50
8... Drain of MOSFET of source follower circuit,
109.509... Source follower circuit MOSFET
Source, 110.510...Load resistance, 111.511...Output, terminal. Figure 1 Figure 2 Figure 3■ s4 Figure 5 Figure 6

Claims (1)

[Claims] an output gate provided adjacent to a final-stage transfer electrode of a charge-coupled device; and a floating diffusion region in which signal charges existing under the final-stage transfer electrode transferred via a barrier under the output gate are accumulated. , a MOSF including a drain region that is electrically connected to the floating diffusion region through a channel under a reset gate to which a voltage is applied, and a gate that is connected to the floating diffusion region.
An output circuit of a charge transfer device comprising a source follower circuit using an ET, wherein a channel of a MOSFET used in the source follower circuit is of an opposite conductivity type to a transfer channel of the charge coupled device. circuit.