Regenerating Amplifier for CCD Arrangements

This invention relates to a regenerating amplifier for charge-coupled-device arrangements (CCD arrangements).

In CCD arrangements which operate without a basic charge, at short intervals regenerating amplifiers are required, the surface space requirement of which must be as small as possible. In addition, these amplifiers should be insensitive to start voltage fluctuations and supply voltage fluctuations.

It is the purpose of this invention to provide a regenerating circuit for a CCD arrangement whose space requirement is small and which amplifies the change in voltage of a capacitance which has been pre-charged to a reference voltage. This objective is achieved by a regenerating circuit of the type hereinafter to be described.

A fundamental advantage of the invention consists in that the reference voltage is produced in such a manner that effects of changes in the start voltage and in the supply voltage are eliminated. Also, the amplifier transistor is advantageously biased in such a manner that it possesses a maximum amplification.

In the following, the invention will be explained in detail making reference to the description and the Figures.

FIG. 1 shows a circuit diagram of a dynamic amplifier in accordance with the invention;

FIG. 2 shows a time diagram for the operation of the dynamic amplifier shown in FIG. 1;

FIG. 3 schematically illustrates the interconnection of a dynamic amplifier in accordance with the invention and two CCD arrangements;

FIG. 4 shows a time chart of the circuit of FIG. 3;

FIGS. 5a to 5e show the surface potentials which occur at the individual points of the two CCD arrangements at different times; and

FIG. 6 diagrammatically illustrates a layout for a CCD regenerating amplifier embodying the present invention.

The illustrated embodiment of a regenerating amplifier 2 embodying the teachings of the present invention is illustrated in FIG. 1. The amplifier 2 has an input terminal 24 and an output terminal 25'. The amplifier 2 includes a transistor 26 which can be controlled by the potential .phi.26 connects the input 24 to the gate of transistor 27 at the connection point 28. The transistors 21 and 22 serve to produce a reference voltage across the capacitance 23. For this purpose, these transistors 21 and 22 have their source terminals connected together, and they also have their drain terminals connected to each other, as shown in the drawing. In this way, these transistors act as opposingly connected diodes. The gate terminal of the transistor 22 is connected to the point 25, which is connected to a potential .phi.25, from which the reference voltage is produced. The gate terminal of the transistor 21 is connected to the point 28. The transistor 27 connects the output terminal 25 to the terminal 271, to which the potential .phi.27 is connected. The current sink 13, which is connected to the input 24, represents the binary states "1" and "0" by the presence and absence of a current I.sub.s. As will be described in detail further in the description, this current sink represents the output of the CCD arrangement.

In the following, the mode of functioning of the dynamic regenerating amplifier in accordance with the invention will now be described, making reference to FIGS. 1 and 2. At the time t.sub.0, the control signals .phi.25 and .phi.27 have a voltage of U.sub.DD, as a result of which the parasitic capacitance 23 is biased via the transistor 22 to a voltage of U.sub.DD - U.sub.T and the parasitic capacitance 29 is biased to a voltage of U.sub.DD - 2 U.sub.T. Here U.sub.T signifies the start voltage of the transistors 22 and 27. At the time t.sub.1 the control signal .phi.25 has a voltage of U.sub.B as a result of which the capacitor 23 is recharged to a voltage of U.sub.B + U.sub.T with the aid of the transistor 21. The transistor 22 is then blocked. The voltage across the capacitor 29 here remains unchanged. When the transistor 26 has been switched on at the time t.sub.2, the capacitor 23 is discharged or is not discharged, in accordance with the binary state of the current sink 13. At the time t.sub.3 the control signal .phi.27 has a voltage of U.sub.B - .delta..

If the capacitor 23 has not been discharged, a voltage of U.sub.E - .phi.27 = (U.sub.B + U.sub.T) - (U.sub.B - .delta.) = U.sub.T + .delta. is connected between gate and source of the transistor 27. As this voltage exceeds the start voltage U.sub.T by the amount of .delta., the transistor 27 goes conductive, as a result of which the capacitance 29 is discharged to a voltage of U.sub.A = U.sub.B - .delta..

If, on the other hand, the capacitor 23 has been discharged by an amount of .DELTA.U, a voltage of U.sub.E - .phi. 27 = (U.sub.B + U.sub.T) - .DELTA.U - (U.sub.B - .delta.) = U.sub.T - .DELTA.U + .delta. can be noted between the gate and the source of the transistor 27. If it is assumed that .DELTA.U is greater than .delta., the transistor 27 is non-conductive, and the capacitor 29 retains the voltage of U.sub.A = U.sub.DD - 2 U.sub.T.

Thus, we have,

(1) for .DELTA.U = 0, an output voltage of U.sub.A = U.sub.B - .delta., and

(2) for .DELTA.U > .delta. an output voltage of U.sub.A = U.sub.DD - 2 U.sub.T.

As the magnitude of the output voltage U.sub.A = U.sub.B - .delta., or U.sub.A = U.sub.DD -2 U.sub.T is dependent only upon .DELTA.U, fluctuations in voltage supply and start voltage advantageously have no influence on the function of the dynamic regenerating amplifier in accordance with the invention.

The voltage change .DELTA.U can be calculated or predetermined for the various cases of use, so that the voltage can be predetermined and thus the pulse generation circuits for .phi. 25 and .phi. 27 can be integrated on the same chip.

In the following, the use, of the dynamic regenerating amplifier as a regenerating stage in CCD registers, will be described in association with FIGS. 3, 4 and 5.

FIG. 3 illustrates the use of the dynamic regenerating amplifier shown in FIG. 1 as a regenerating stage for the CCD arrangement without a basic charge generation. Details of FIG. 3 which have already been described in association with the other Figures bear the corresponding references. The last electrode 12 of the CCD output stage 1 here assumes the function of the transistor 26 and that of the current sink 13 in FIG. 1, whereas the transistor 27 in FIG. 1 represents the input stage of the CCD arrangement 2 with the diffusion zone 31 and the gate electrode 32. The capacitance 29 is governed by a potential well located beneath the electrode 33.

The regeneration of the CCD output signals of the CCD citcuit 1 will now be explained with the aid of the time diagram shown in FIG. 4, and the associated surface potentials .phi. 5 shown in FIGS. 5a to 5e. At the time t.sub.0 (FIG. 5a) the capacitance 23 is biased to the voltage U.sub.DD - U.sub.T. When the signal .phi. 25 has been reduced to a voltage of U.sub.B (time t.sub.2, FIG. 5b), the gate voltages .phi. 121 and .phi. 331 are connected to the gate electrodes 12 and 33. To avoid electrons from passing from the diffusion zone 11 into the potential well beneath the electrode 12, the gate voltage .phi. 121 has a value which produces a surface potential which is smaller than that of the diffusion zone 11. If electrons representing a binary "1" reach the output diffusion zone 11, the parasitic capacitance 23 composed of the capacitance of the diffusion zone 11 and the parasitic capacitances of the transistors 21, 22 and of the capacitance of the electrode 32, is discharged. If, at the time t.sub.2, no electrons (binary "0") reach the output diffusion zone 11, the voltage U.sub.E = U.sub.DD - U.sub.T remains unchanged. As can be seen from FIG. 5c, a potential well exists beneath the electrode 32 and a potential barrier with a surface potential of .phi..sub.B exists beneath the electrode 32. This surface potential has a value of .phi..sub.B = .phi..sub.B1 or .phi..sub.B = .phi..sub.B0, in dependence upon whether charge or no charge reaches the diffusion zone. At the time t.sub.3 (FIG. 5d), the diffusion zone 31 is pulsed with the aid of the signal voltage .phi. 311 to a voltage of U.sub.B - .delta., as a result of which it assumes a surface potential of .phi..sub.31. If .phi..sub.31 > .phi..sub.B, i.e., .phi..sub.B = .phi..sub.B1, charge carriers pass from the diffusion zone into the potential well.

Otherwise, when .phi..sub.31 < .phi..sub.B and .phi..sub.B = .phi..sub.B0, no charge carriers can pass into the potential well. At the time t.sub.4, the signal voltage .phi. 311 again has a value of U.sub.DD, as a result of which the surface potential .phi. 31 is of sufficient magnitude for the diffusion zone to be cut off from the potential well (FIG. 5e).

FIG. 6 illustrates the construction of the CCD regenerating amplifier of FIG. 3 in a silicon-gate-technique. Details of FIG. 6 which have already been described in association with FIG. 3 bear the corresponding references. The CCD circuit 1, the regenerating amplifier 2 of the invention, and the CCD circuit 3 are constructed on a substrate 19. This substrate is preferably a p-conducting silicon substrate. The n-diffusion zones represented by obliquely shaded areas are introduced into this substrate. The n-diffusion zone 11 of the CCD arrangement 1 simultaneously serves as source zone of the transistor 21. The n-doped drain zone of this transistor simultaneously represents the terminal 25 and the drain terminal of the transistor 22. The source zone of the transistor 22 is connected via the contact hole 221 outlined by the dotted area 221, to the aluminum line 111 and thus via the contact hole 211 to the diffusion zone 11 and to the source zone of the transistor 21. The silicon gate electrode, indicated by the dash-dotted line 212 of the transistor 21, is likewise connected via the contact hole 211 to the aluminum conductor path 111. The silicon gate electrode, represented by the dash-dotted line 223, of the transistor 22 is electrically connected via the diffusion silicon gate contact 22, arranged next to the n-diffusion zone 31, of the CCD arrangement 3 is connected to the aluminum conductor path 111 via the contact hole 321 shown by the dotted area. The electrode 32 is likewise a silicon electrode which is represented by the dash-dotted line.

It will be apparent to those skilled in the art that many modifications and variations may be effected without departing from the spirit and scope of the novel concepts of the present invention.