JPS62214664A - Driving circuit for charge coupled device - Google Patents

Abstract

PURPOSE:To drive a CCD with low power consumption even if a pause time is provided in a driving signal by connecting a series circuit of an inductance and a capacitance between the electrodes of the CCD. CONSTITUTION:Driving electrodes 3, 4 are formed through an oxide insulating film 2 on a silicon substrate 1, and charge is transferred through a potential well of a silicon substrate, generated by applying driving waveforms phi1, phi2. An MOS capacitance C1 is formed of the electrode 3, the film 2 and the substrate 1 in a CCD equivalent circuit of such an electrode structure, and an MOS capacitance C2 is formed of the electrode 4, the film 2, and the substrate 1. An inductance L and a capacitance C are connected in series. Since an energy is concentrated in the frequency of 1/t1 when the driving signal is applied to the circuit in this configuration, if circuit constant are set so that reactance X increases in this frequency, a current which contributes to charging/ discharging of the CCD hardly flows to the driving circuit, thereby alleviating power consumption.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drive circuit for a charge-coupled device, and particularly to a drive circuit for reducing power consumption.

[Conventional technology]

Charge-coupled devices (hereinafter referred to as CCDs) are small.

In recent years, it has been widely used in image sensors etc. due to its features such as light weight and low power consumption.However, the drive circuit that transfers charge cannot necessarily be said to have low power consumption.The reason is that the drive circuit has a COD charge transfer electrode capacitance. This is also because power is consumed when charging and discharging the interelectrode capacitance.

Therefore, in order to solve these problems, for example,
In the coupling method of the i-charge transfer element disclosed in Publication No. 6-80893, an inductance is provided between the electrodes, and the resonance point due to the inductance and inter-electrode capacitance is made equal to the transfer frequency, thereby reducing electrode consumption. .

[Problem that the invention seeks to solve]

However, although this driving method is useful for applications that continuously transfer signals, such as a CCD delay line, it is useful for applications such as image sensors where the driving signal is periodically paused.
In D, current flows through the inductance while the drive signal is paused, so there is a problem that power consumption increases on the contrary.

This invention has been made to solve the above-mentioned problems, and aims to provide a charge-coupled device drive circuit that can drive a CCD with low power consumption even if the drive signal has a pause period. It is something.

[Means for solving problems]

A charge-coupled device drive circuit according to the present invention has a series circuit of an inductance and a capacitance connected between electrodes of a COD.

[Effect]

In this invention, the capacitance in the series circuit prevents the COD electrode current from flowing during the pause period of the drive signal, thereby achieving low power consumption of the charge coupled device.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

First, prior to explaining a drive circuit for a charge coupled device according to an embodiment of the present invention, the structure of a CCD will be explained.

FIG. 3 shows a cross-sectional view of the electrodes of a two-phase CCD.

In the figure, reference numeral 3.4 denotes drive electrodes, which are formed on the silicon substrate 1 via the oxide insulating film 2, and charges are transferred to the electrodes using a drive waveform φ1. It is transferred through a potential well in the silicon substrate created by applying φ2.

The equivalent circuit of a COD with such an electrode structure is the fourth
Illustrated in the figure. In FIG. 4 (al), C8 is electrode 3.
Insulating oxide film 2. A MOS capacitance C2 formed of a silicon substrate 1 is an electrode 4. Insulating oxide film 2. This is a MOS capacitor formed from a silicon substrate. Also, C
3 is an interelectrode capacitance formed by the overlap of electrodes 3.4, etc.

Here, if c and hc2, then C, +C3=C2 plus c3=c
A capacitance of @ can be assumed, and this is considered to be the equivalent capacitance of a two-phase CCD. FIG. 4 (bl is an equivalent circuit expressed using this equivalent capacitance C).

Next, drive signals φt and φt applied to the electrodes 3 and 4 are shown in FIG.

FIG. 5(a) shows the transfer period t1. Between the resting bodies t, the drive signal φ3. with a repetition period T. φ2 is shown, and φ1 and φ2
The phase differs by 180'. Applying this signal waveform to the horizontal transfer COD of the image sensor, t is one pixel transfer period, 1. is a horizontal blanking period, and T corresponds to one horizontal period. Figure 5(b) is an analysis of the energy distribution of the drive signal in Figure 5(a) in the frequency domain, with 1/T
and 1/l.

It can be seen that energy is concentrated at the frequency of

FIG. 1 shows a drive circuit for a charge-coupled device according to an embodiment of the present invention. This figure shows its configuration using the equivalent circuit of FIG. 4 (bl). In FIG.
, 4, if the resistance bones are ignored, the impedance Z becomes only the reactance X, which is expressed as .

Figure 2 (a) is a graphical representation of the relationship in the above equation,
"+" of reactance X indicates inductive property, and "-" indicates capacitive property. Also, foo is the frequency at which reactance It will be done.

Further, fo is the frequency at which the reactance X becomes O, that is, the series resonance point between the inductance L and the capacitance C, which is given by ".-□ 2πττ.

When the drive signal in Figure 5 is applied to the circuit in Figure 1, it is known from Figure 5(b) that the energy is concentrated at a frequency of 1/tl, so the reactance X at this frequency is If the circuit constants shown in FIG. 1 are set so as to be large, almost no current contributing to charging and discharging the CCD will flow into this drive circuit, reducing power consumption. That is,
Increasing the reactance X at 1/11 means setting the parallel resonance point at the transfer frequency, and the constant in this case satisfies the following equation or is given by C.

■ f oo -- The frequency at which the reactance X becomes 0 in the 1° order (series resonance point) is preferably set to the frequency at which the power is the least as shown in FIG. 5(b). The relationship between the power consumption P when the drive signal is the horizontal drive signal of the image sensor and the series resonance point f0 is expressed as the second
Shown in Figure (b). From this, it can be seen that ro should be set at the center between the transfer frequency and the pause repetition frequency, and the constant in this case satisfies the following equation or is given by C.

It can be seen that by setting the parallel resonance point at the transfer frequency and the series resonance point at the center between the transfer frequency and the pause repetition frequency as described above, the circuit shown in FIG. 1 achieves low power consumption.

In the above embodiment, the case of a two-phase CCD was explained, but even in the case of a four-phase CCD or a three-phase CCD, the equivalent capacitance conversion of the drive electrode is performed in the same manner as in FIG. 4, and the equivalent capacitance tco
It is only necessary to connect an inductance and a capacitance connected in series to each of the above, and the same effect as in the above embodiment can be obtained.

〔Effect of the invention〕

As described above, according to the charge-coupled device drive circuit according to the present invention, by connecting an inductance and a capacitance connected in series to a drive electrode, a CCD used in an image sensor or the like can be driven with low power consumption. I can do it.

[Brief explanation of drawings]

FIG. 1 is an equivalent circuit diagram of a drive circuit for a charge-coupled device according to an embodiment of the present invention, and FIG. 2 is a diagram illustrating the characteristics of FIG. 1.
FIG. 3 is a sectional view of the electrodes of the COD, FIG. 4 is a diagram showing the equivalent capacitance of a two-phase CCD, and FIG. 5 is a diagram showing the drive signal waveform and its energy distribution. In the figure, L is inductance, C is capacitance, and C0 is the equivalent capacitance of the CCD. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (2)

[Claims] (1) In a circuit that drives a charge-coupled device by generating a plurality of drive signals having a rest period and different phases, each drive signal is connected to a drive electrode of the charge-coupled device and to which the plurality of drive signals are applied. A charge-coupled device drive circuit comprising a series circuit including an inductance and a capacitance connected between lines. (2) The series circuit has a series resonance point set between the pause repetition frequency and the transfer frequency of the drive signal, and a parallel resonance point of the parallel circuit consisting of the series circuit and the equivalent capacitance of the charge-coupled device. 2. The drive circuit for a charge-coupled device according to claim 1, wherein circuit constants thereof are set to be near the transfer frequency.