JPS5822884B2 - Input weighting method of charge transfer type transversal filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an input weighting method for a charge transfer type transversal filter in which each weighting coefficient of a signal charge can be programmed by an external electric signal.

As is well known, charge transfer devices (hereinafter referred to as CTD) such as charge-coupled devices (hereinafter referred to as CCD) and bucket brigade devices (hereinafter referred to as BBD) utilize their delay fitting ability to perform transversal transfer. It can be applied to filters.

Recently, a transversal filter with high integration and excellent frequency percentage has been developed by weighting multiple branched input signals using predetermined coefficients, and sequentially adding and delaying them using CTD. has been done.

This is called an input weighted charge transfer type transversal filter, and MOSFET is used as the input signal weighting circuit.
By using a variable impedance element such as the above, a transversal filter in which each weighting coefficient can be programmed can be easily constructed.

However, due to its structure, input weighting circuits using variable impedance elements such as MOSFETs require an area several to ten times larger than the delay and addition sections made up of charge transfer elements, and are difficult to integrate. This significantly reduces the degree of integration as a circuit.

FIG. 1 is a general block diagram of an input weighted charge transfer type transversal filter.

The human input signal is inputted to the input weighting circuits 2a, 2b, 2c, and 2d from the terminals 1atlb, 'Ic, and ld, respectively, and the gain of this signal is controlled by the electric signal given from each of the terminals 3a, 3b, 3c, and 3d, and the signal charge is converted into a signal charge. The signal is input to each stage of the charge transfer element 4.

The signal charge input to each stage of the charge transfer element 4 reaches the output terminal while being delayed and added in sequence, and is taken out by the output detection circuit 5 from the terminal 6 as an output signal.

With such a configuration, the output signal addition circuit required in the output weighting type transversal filter is not required, so the number of circuit elements is significantly reduced.

Furthermore, since the charge transfer device itself is an extremely highly integrated device, the input weighted charge transfer type transversal filter shown in FIG. 1 can be said to have a circuit configuration extremely suitable for integration into an integrated circuit.

However, when a variable impedance element such as a MOSFET is used as an input signal weighting circuit, its integration density is lower than that of a charge transfer element, so if the number of delay stages is large, the chip size integrated circuit as a whole becomes quite large. There are drawbacks such as:

This invention was developed in view of the above points, and maintains a high degree of integration of charge transfer elements by providing electrodes for electrically controlling the gain of signal charges in the signal charge injection means provided at each stage. Another object of the present invention is to provide an input weighting method for a charge transfer type transversal filter in which the weighting coefficient of each stage can be arbitrarily set.

Furthermore, by providing two independent sets of input weighting means corresponding to each inverted input signal at each stage and selecting and using one of them, positive and negative weighting coefficients can be set arbitrarily. The purpose of this paper is to provide an input weighting method for a transfer type transversal filter.

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

FIG. 2 is a diagram showing the basic circuit configuration of the present invention.

The input signal Vin is superimposed with the bias voltage VB and is applied from the terminal 11 to the signal charge injection means 120 of each stage, and the inverted input signal Vin is also superimposed with the same bias voltage VB and is applied to the other signal charge injection means 120 of each stage from the terminal 11'. Signal charge injection means 12
′ is given.

Each of these signals corresponds to an electrode 13, 13' that corresponds to a switch.
Either one is selected by , and is then inputted to a variable capacitor 15.15' via an electrode 14.14' corresponding to a sampler.

The signal charges input to the variable capacitors 15 and 15' are output to the charge transfer element through electrodes 16 and 16' each corresponding to a sampler.

The capacitance of the variable capacitor 15.15' changes depending on the control voltages Vhk and Vhk' applied through the terminals 1γ and 11', and the charge Qs i g stored in each capacitor 15.15' is expressed by the following equation. It will be done.

Q s i g (+; 2C [■hk]・(Vc (
v1n+VB)) -(]) or Qsig HC(
Vhksu・(vo (vin+VB))-(2) Kokote C [■hk] Oyohi C [■hk'] Ha■hk no vhk
The quantity determined by the value of 'Vo represents the charging voltage of the capacitance 15.15'.

Charge Qsig (-1-1 is the input signal Vi when the electrode 13 corresponding to the switch is closed) expressed by the formula (1)
The charge QsigH expressed by equation (2), which is the accumulated charge for n, is the accumulated charge for the inverted input signal vin when the electrode 13' corresponding to the switch is closed.

Therefore, the charge sent to the charge transfer element is
' selects the polarity of the input signal, and the control voltage Vhk
, Vhk'.

Therefore, the signal charge injection means 12.1 having the configuration shown in FIG.
By providing 2' in each stage of the charge transfer element, it is possible to realize an input weighting system of a charge transfer type transversal filter that has a high degree of integration and can weight arbitrary positive and negative coefficients.

FIG. 3 is a plan view showing the configuration of an embodiment of the present invention.

In the figure, 12a to 12d are signal charge injection means, 1
8 is a charge transfer element, and 19 is an output detection circuit.

The first stage signal charge injection means 12a each include a set of source regions 20a, 20a' and first gate electrodes 21a, 21a'.
, second gate electrode 22a.

22a', third gate electrode 23a, and fourth gate electrode 2
4a.

Similarly, the second to fourth stage signal charge injection means 12b~
12d are 'north regions 20b, 20b', 20c, 20
c', 20d, 20d', first gate electrodes 21b, 21
b'21c, 2'lc', 21d, 21d', second gate electrodes 22b, 22b', 22c, 22c', 22d.

22d', third gate electrodes 23b to 23d, and fourth gate electrodes 24b to 24d, respectively.

The first gate electrodes 21a to 21d, 21a' to 21
d' includes selection signals VS4 to ■80, ■'s4 for selecting one of the two sets of signal charge injection means in each stage.
~V'81 is given.

This signal is used by switch 2 to switch between DC voltage ■8 and ground.
It is made by switching each of 5a to 25d.

Second gate electrodes 22a to 22d, 22a'
~22d' is applied with a human input signal ``in'' biased by a DC voltage vB or an inverted input signal door.

In addition, a control voltage ■h4. is used to set the capacitance under the third gate electrodes 23a to 23a to a desired value. ■h3゜V
h 21 Vh t is applied.

The capacitance C (Vhk) under the third gate electrode 23a23d varies depending on the control voltage Vhkj, and within a certain range of Vhk, it is approximately C[■hk]2K·Vhk...
3).

Here K is a constant. Therefore, the signal charge accumulated under the third gate electrode changes as shown in FIG. 4 depending on the polarity of the input signal and the control voltage.

In other words, the custom-made curve shown by the solid line in Fig. 4 is Qsi
The characteristic curve that shows the change in
Each represents a change in .

A pulse φ is applied in parallel to the source regions 20a to 20d and 20a' to 20a', and the fourth gate electrode 24a
~24d, pulse φ is applied in parallel.

-3 is applied to the source regions 20a to 20d,
From each of 20a' to 20d' to each second gate electrode 22a to
While charges are being injected under each of the third gate electrodes 23a to 23d through 22d22a' to 22d', each of the fourth gate electrodes 24a to 24d is closed, and the source region 20
During the period when charge injection from each of a to 20d and 20a' to 20d' is stopped, each of the fourth gate electrodes 24a to 24d is opened and the charges accumulated under each third gate electrode 23a to 23d are transferred to the transfer electrode 26a. Transfer injection to ~26d.

The signal charges injected into each of the transfer electrodes 26a to 26d are delayed by the subsequent transfer electrodes 2γa to 2γd and 28a to 28d,
After being added, the signal enters the floating diffusion region 29 and is taken out as a transversal filter output from the output terminal 32 of a north follower amplifier consisting of an MO8FET 30 and a resistor 31 connected thereto.

Further, the charge input to the floating diffusion region 29 is reset every clock by the reset gate electrode 33 and the drain region 34 in synchronization with the pulse φR applied to the reset gate electrode 33.

As described above, each stage is provided with a signal charge injection means for an input signal and a signal charge injection means for an inverted input signal.
By selecting either one and controlling the gain of the charge injected into the signal charge injection means using a control voltage, an input weighting method for a charge transfer type transversal filter with arbitrary positive or negative weighting coefficients is realized. can.

By the way, the input weighting method of the transversal filter shown in Fig. 3 is based on the potential under the second gate electrode and the third gate electrode.
Near the cutoff voltage, where the potential under the gate electrode approaches, the linear relationship between the input signal and the signal charge may deteriorate.

FIGS. 5 and 6 are circuit configuration diagrams showing other embodiments of the present invention, respectively, and show one method for improving the above-mentioned linear relationship.

The same input signals Vin and Vin applied to the second gate electrodes 22a and 22a' are partially superimposed on the control voltage applied to the third gate electrode 23a.

As a result, the second gate electrode 22a22 near the cutoff
When the input signal a' changes, the voltage at the third gate electrode 23a changes proportionally, improving the linear relationship between the input signal and the signal charge.

As described in detail above, by using the signal charge weighting method of the charge transfer type transversal filter of the present invention, it is possible to easily obtain a transversal filter with a high degree of integration and a programmable weighting coefficient.

Note that the present invention is not limited to the embodiments described above; for example, although the charge transfer element has been described using a three-phase drive type CCD, this invention can be applied to single-phase, two-phase, and four-phase one-drive type CCCDs.
It may be D or even BBD.

Further, the electrode structure does not have to be a single metal electrode.

Needless to say, a stacked electrode structure may also be used.

As described above, according to the present invention, it is possible to increase the degree of accumulation and to provide an input weighting method for a charge transfer type transversal filter in which the weighting coefficient is programmable.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an input weighted charge transfer type transversal filter, FIG. 2 is a basic circuit diagram of an embodiment of the present invention, and FIG. 3 is a diagram of the configuration of an embodiment of the invention. A plan view and FIG. 4 are characteristic diagrams for explaining the above embodiment, and FIGS. 5 and 6 are circuit configuration diagrams showing other embodiments of the present invention. 2a to 2d... Input weighting circuit, 4, 18...
...Charge transfer element, 5, 19...Output detection circuit, 12°12', 12a-12d...Signal charge injection means, 13.13', 14.14', 16 .16
'... Electrode, 15.15'... Variable capacitance, 20 a to 20 d, 20 a' to 20 d'...
...source region, 21a-21b, 21a'-21d
'...First gate electrode, 22a to 22d. 22 a′ to 22 d′-” second gate electrode, 23 a to
23d...Third gate electrode, 24a to 24a.
...Fourth gate electrode, 25a to 25d...
・Selector switch, 26a to 26d, 2γa to 2γd, 2
8a-28d...Transfer electrode, 29...
Floating diffusion region, 30...MOSFE
T, 31...Resistor, 33...Reset gate electrode, 34...Drain region.

Claims (1)

[Claims] 1. Charge transfer means for delaying and adding signals, input means for weighting input signals with desired coefficients and inputting them corresponding to each stage of the charge transfer means, and the delayed and added signals. In the input weighted charge transfer type transversal filter, the input means includes an electrode for temporarily accumulating a charge proportional to the input signal, and the input means includes an electrode for temporarily accumulating a charge proportional to the input signal. The capacitance is varied to a desired value by an external electric signal, and two sets of input means are provided for each stage of the charge transfer means, and either one of the two sets of input means is connected to the input means. An input weighting method for a charge transfer type transversal filter, characterized in that it is selectively used. 2. The two sets of input means provided for each stage of the charge transfer means each include a source region, a first gate electrode, a second electrode, and a third gate electrode connected adjacently to the source region in sequence. and a fourth gate electrode, a selection signal for selecting one of the input means is applied to the first gate electrode of one input means, and an input signal biased by a DC signal is applied to the second gate electrode. and applying an inverted signal of the selection signal to the first gate electrode of the other input means,
An inverted input signal biased by a DC signal is applied to the second gate electrode, and an electric signal is applied to each third gate electrode to set the capacitance of the potential well formed under this electrode to a desired value. , each fourth gate is closed while charges are injected from each source region under each selected third gate electrode through under each selected first gate electrode and second gate electrode, and charges are injected from each source region. 2. An input weighting system for a charge transfer type transversal filter according to claim 1, wherein each fourth gate is opened during a period when injection of the charge is stopped to transfer charges to the bottom of each transfer electrode. 32. The input of the charge transfer type transversal filter according to claim 2, wherein part or all of the input signal applied to the second gate is superimposed on the electric signal applied to the third gate electrode. Weighted method.