JPS5945249B2 - Filter using charge transfer device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a filter using a charge transfer device, particularly a transversal filter.

Charge Transfer Device (ChargeTransferDevi)
A conventional transversal filter using CE) is generally configured as shown in FIG.

In this figure, SB is a semiconductor substrate, and CTD is a charge transfer device, which includes a transfer electrode TE, a linear charge transfer channel formed in the substrate under the transfer electrode, wirings 11 and 12 to the electrode, and the like. In this example, the charge transfer device uses a two-phase drive system, and therefore there are two wires 11 and 12 that supply the transfer voltage, and the first phase transfer electrode TEI and the second phase transfer electrode TE2 are connected to these, respectively. be done. In the figure, electrode TEI,
TE2 is shown as consisting of two parts, but this indicates that the thickness of the insulating film under the electrode is different in order to determine the direction of charge transfer as is known, and therefore the electrode has a step. . An input gate electrode IGE, a source diffusion region SDR, and an output gate electrode OGE) and a drain diffusion region DDR are provided at input/output portions at both ends of the charge transfer device. Also, a number of field effect transistors (FETs) are formed on the substrate SB along the linear charge transfer device, and the gate electrodes of these FETs are connected to charge sensing diffusion regions SD provided for each bit in the channel. Ru. Furthermore, a large number of bonding pads BP are provided mainly on the three sides of the rectangular substrate SB on the non-charge transfer device side, and these pads are commonly used for all the drain electrodes of FETs, the sources of individual transistors, and the charge transfer device side. It is connected to the source, drain, input/output gate electrodes, and first and second phase electrode wiring via long lead wires RD. The operation of this device is as known. When the gate IGE is manually opened and charge is injected from the source to the channel, this charge is attracted to the deep depletion layer alternately formed by the electrodes TEI and TE2 to which the transfer voltage is applied. The charge is transferred from the input end to the output end, during which it is detected by each diffusion region SD for charge sensing, taken out via the FET, lead wire RD, and bonding pad BP, weighted and combined, and sent to the transversal filter. functions as.

However, as is clear from the drawings, this device tends to be long and thin, and the electrode wiring 1 of the charge transfer device CTD
It is difficult to take out the taps on the 1 and 12 sides, so the transistor FET is arranged only on one side of the charge transfer device as shown in the figure, and the bonding pad BP is mainly placed on the three sides excluding the side where the charge transfer device is located. It is connected to the corresponding part by a long lead wire RD.

Therefore, this method has a low degree of integration, requires long lead wires, and is therefore prone to delays, mutual interference, noise pickup, etc. To prevent this, for example, the charge transfer device may be rounded to shorten its length, but with conventional charge transfer devices, changing the transfer direction is troublesome and such a process is difficult to take. By the way, unlike the conventional CTD in which the channel is straight, the CTD has a channel in which the electrode is straight and curved.
The inventor previously proposed TD.

In this type of CTD (hereinafter referred to as a meander channel type CTD), changing the transfer direction is extremely easy. What about this invention?
Focusing on this point, we constructed an annular CTD using a meander channel CTD, formed an FET group on the outside of it, and formed a bonding pad section on the outside of it.In this way, the degree of integration was improved, and since it is close to square, The present invention provides a filter whose substrate also has high mechanical strength. A filter using the charge transfer device of the present invention has a meandering charge transfer channel formed in a long annular shape in the center of a semiconductor substrate, a pair of semi-concentric annular transfer electrodes provided on the channel, and these channels and electrodes A plurality of field effect transistors for weighting are arranged on the entire outer periphery of the substrate portion of the annular charge transfer device constituted by, and a plurality of bonding pads are further provided on each side of the edge portion of the substrate. The gate of the transistor is connected to a charge sensing diffusion region formed in the channel, and the source and drain are connected to the pad, which will be explained in detail below with reference to embodiments. .

FIG. 2 shows an embodiment of the present invention, in which the same parts as in FIG. 1 are given the same reference numerals. As shown in this figure, in this embodiment, a charge transfer device CTD is formed in a rectangular ring shape at the center of the tenon of the semiconductor substrate SB, and field effect transistors FET are similarly arranged in a rectangular ring shape around the outer periphery of this charge transfer device. The bonding pads BP are similarly arranged in a rectangular ring shape around the substrate. This charge transfer device is a meander channel type charge transfer device previously proposed by the present inventor, and is formed by parallel channel stops CS, , CS on both sides and alternately protruding channel stops CS3, CS4 as shown by dotted lines. It includes a shaped channel CH and a pair of parallel transfer electrodes TEa and TEb formed on this channel with an insulating film interposed therebetween. These band-shaped transfer electrodes have a rectangular ring shape and a concentric shape as shown in FIG. Bonding pad BP installed here using the central void of the annular CTD
Connect to 2. Connection between this bonding pad and an external circuit is made by a wire that connects the CTD, transistor group, etc. Of course bonding pad BP
2 can also be provided outside the ring. The charge detection diffusion region SD provided in the channel CH is a transistor FET.
The drains of each transistor are collectively connected to the bonding pad BP3 around the substrate,
Similarly, the source of each transistor is padded BP4,
BP,..., the source diffusion region SDR of the CTD is connected to the pad BP,O, and the input gate electrode 1GE is connected to the pad BP1,
The drain diffusion region DDR is connected to the pad BPl2, and the output gate electrode 0GE is connected to the pad BPl3.

The operation is the same as that of the previously proposed meander channel CTD and transversal filter, with source and drain voltages S, D, input and output gate voltages 1G, 0G1 first,
When two-phase transfer voltages φ1 and φ2 are applied, charges are injected from the source diffusion region into the channel CH through the input gate, and the charges are transferred in a meandering manner along the channel.
During this time, each bit is detected by a charge sensing diffusion region provided for each bit and a transistor connected thereto, weighted, and then combined to perform the function of a known transversal filter. As is clear from a comparison between FIG. 2 and FIG. 1, in the present invention, the elongated CTD 5 is bent into an annular shape, so that transistor groups and bonding pad groups can be similarly arranged annularly around the outer periphery of the CTD 5. Can be summarized compactly.

In such equipment, the bonding pad is the most important thing that requires a large area, at least 100 x 100μ.
It requires about 100 m. However, if they are arranged around the entire circumference of the board as in the present invention, the number of pads is 38 in a 31-stage CTD as shown in the figure, and if these are arranged at equal intervals, 10 vertically and 11 horizontally, the board will be 2x2. 211 rectangular plates are sufficient, and the substrate area can be halved compared to the case of FIG. Further, the lead wires RD can be wired in a radial pattern as shown in the figure, that is, over the shortest distance, and there is no need to make a large bend as shown in FIG. Further, since each element and wiring are evenly distributed over the entire surface, sufficient space is available even when a resistor for assigning a weighting coefficient to each tap is provided on the substrate, which facilitates processing. In this respect, in the one in Fig. 1, one side of the CTD (the upper part of the drawing) is occupied by the wiring 11 and 12 that supplies the transfer voltage, and the transistor group is concentrated only on the other side, and if a weighting resistor etc. is placed in this area, becomes even more complex. Also, since the board can be made into a square shape, it is less likely to break than if it were long and thin.
Mechanical strength increases. As described above in detail, according to the present invention, it is possible to obtain a filter with an increased degree of element integration and a high degree of freedom in element arrangement.

Of course, the present invention is not limited to the illustrated embodiment and can be modified in various ways.
For example, the charge transfer device is not in the shape of a square ring, but may be in any polygonal shape, or even in a circular shape.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing the structure of a conventional transversal filter, FIG. 2 is a plan view showing the structure of the transversal filter of the present invention, and FIG. 3 is a plan view showing the shape of a part of the electrodes. In the drawing, SB is a substrate, CH is a channel, TEa and TEb are transfer electrodes, FET is a field effect transistor, SD is a charge sensing diffused resistor, and BP is a bonding pad.

Claims (1)

[Claims] 1 A meander-shaped charge transfer channel is formed in the center of a semiconductor substrate, a pair of substantially concentric ring-shaped transfer electrodes are provided on the channel, and the entire annular charge transfer device constituted by these channels and electrodes is A plurality of field effect transistors for weighting are arranged on the substrate portion on the outer periphery,
Furthermore, a plurality of bonding pads are provided on each edge of the substrate, and the gate of the transistor is connected to a charge sensing diffusion region formed in the channel, and the source and drain are connected to the pads. A filter using a characteristic charge transfer device.