JPS6122490B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Field of Application of the Invention The present invention relates to a signal detecting section in a MOS type semiconductor integrated circuit device, etc., which has large switching noise.

(2) Prior art MOS transistors have many advantages such as high gate input resistance and are suitable for high integration, and are used in large-scale integrated circuits. It is often used as a switch element. However, MOS transistors have high switching noise. This switch noise
It is essential to the operating mechanism of MOS transistors. The switch noise will be explained using FIGS. 1 to 3.

Figure 1 shows a cross-sectional outline of a MOS transistor. For convenience of explanation, the following describes the case of an n-channel type in which electrons are used as signal charges, but even in the case of a p-channel type in which holes are used as signal charges, the following can be done by reversing the conductivity type and polarity. The explanation can be applied in exactly the same way.

The MOS transistor is composed of a source 2 and a drain 3 made of an n-type diffusion layer formed on a p-type Si substrate 1, and a gate electrode 4 connected therebetween. In order to transfer the signal charge of the source 2 to the drain 3, a positive pulse is applied to the gate electrode 4, an n-type inversion layer 5 is formed on the surface of the Si substrate directly under the gate charge, and a gap between the source 2 and the drain 3 is formed. That's how you connect. If this inversion layer 5 is not formed, information from the source 2 cannot be transmitted to the drain 3.

However, the electrons forming the inversion layer 5 are of the same type as the signal charge, and since these electrons are extracted from the source 2 and drain 3, when viewed from the drain 3 side, these electrons are temporarily stored under the gate electrode 4. This causes spurious signals. Furthermore, the space capacitance between the gate electrode 4 and its wiring 9 and the drain 3 and its wiring 8 is also
A similar pseudo signal is generated by transmitting a voltage pulse applied to the This is switch noise. source 2
If the amount of signal charge on the side is small, the signal will be buried in this switch noise, making detection difficult. This will be explained in more detail using FIGS. 2 and 3.

FIG. 2 is a schematic diagram of a conventional signal detection method.
Charges stored in a signal source on the source 17 side, for example, a capacitor 20, are guided to the drain 18 side by a positive voltage pulse applied to the gate electrode 19 of the MOS transistor 10, and the load 1 connected to the power supply 12
3. For example, a resistor generates a voltage change on the drain 18 side, which is detected at the output terminal 14. This type of signal charge detection method is used in many applications such as one-transistor type MOS memories and imaging devices consisting of photodiode arrays.

FIG. 3 shows a typical voltage waveform 21 applied to the gate electrode 19 and a typical signal waveform 22 appearing at the output terminal 14. As the voltage applied to the gate electrode 19 rises and falls, spike-like peaks 23 and 24, which are switch noise, appear in the signal waveform 22. Depending on the presence or absence of signal charges on the source 17 side, the signal waveform will be as shown by a solid line (absent) or a broken line (present). In the above-mentioned memory or image pickup device, a large number of pairs of transistors 10 and capacitors 20 are connected in parallel with a common drain 18, and the parasitic capacitance 15 on the drain side is larger than the capacitor 20, and the output signal 25 becomes extremely small. Furthermore, as higher integration and higher speeds are desired, the capacitance 20 becomes smaller. Since it is necessary to increase the number of electrons in the inversion layer to increase the conductivity, the ratio of the output signal 25 to the switch noise peaks 23 and 24 becomes smaller and smaller, making it difficult to detect.

Furthermore, changes and asymmetry in the voltage waveform 21, non-uniformity in the shape of the gate electrode 4 in FIG. peak 23
and 24, which changes the output signal 25, making detection even more difficult.

For this reason, in conventional methods, the capacitor 20 is increased at the expense of lowering the degree of integration and complicating the process, or a complicated signal detection circuit is used.
Currently, efforts are being made to reduce parasitic capacitance.

(3) Purpose of the Invention The present invention provides a means for very easily extracting only signals from signals with large switching noise caused by MOS transistors.

(4) General description of the invention The gist of the invention is to cancel the voltage fluctuation on the drain side of a MOS transistor that accompanies switch operation, which causes switch noise, between the beginning and end of the switch operation. , a junction is connected in series between a reference voltage supply source that applies a reference voltage to the drain of a MOS transistor and the drain, preferably in the forward direction with respect to the signal charge.

(5) Examples Hereinafter, the present invention will be explained in detail with reference to examples.

FIG. 4 shows one embodiment of the present invention. In contrast to the conventional example shown in FIG.
A diode 30 is inserted between them as a junction. The n side of the diode 30, which has a conductivity type in which electrons are majority carriers, is connected to the drain 18, and the p side, which has a conductivity type in which holes are majority carriers, is connected to the load 13 side.

FIG. 5 shows a voltage waveform 31 applied to the gate electrode 19, a voltage waveform 32 on the drain 18 side, and a signal waveform 33 appearing at the output terminal 14 in this embodiment. The solid line shows the case where there is no signal charge, and the broken line shows the case where there is signal charge.

Initially, the voltage on the drain 18 side and the output terminal 14 is the reference voltage, that is, the voltage of the power supply 12.

Output 14 serves as a reference voltage source for drain 18 .

The voltage on the drain 18 side rises above the reference voltage due to the positive voltage pulse applied to the gate electrode 19, but since the diode 30 is reverse biased, the drain 18 side and the output end 14 side are electrically isolated and the output end 14 side is electrically isolated. The voltage is the reference voltage, i.e. the power supply 12
does not change equal to the voltage of . Then when the voltage pulse is removed, if there is no signal charge, drain 1
There is no change in the voltage at the output terminal 14, only the voltage on the 8 side returns to the original value. Only when there is a signal charge, the voltage on the drain 18 side decreases from the original voltage, that is, the voltage at the output terminal 14 as shown at 34, and the diode 3
0 becomes a forward bias and conducts. As a result, a charge corresponding to the signal charge flows through the load 13, and an output signal 35 appears at the output terminal 14. That is, only signal components can be extracted.
It goes without saying that similar effects can be obtained by using a Schottky diode instead of the pn junction diode 30.

A feature of the present invention is that the drain 18 side creates an electrically floating state in response to voltage fluctuations on the drain 18 side accompanying the switching operation of the MOS transistor 10, and the voltage fluctuation in the opposite direction occurs when the switching operation is completed. The purpose is to cancel the voltage change due to the voltage fluctuation. Therefore, it is completely unaffected by changes in the voltage waveform 31, characteristics of the MOS transistor 10, changes in parasitic effects, etc.

Conversely, for this purpose, means for preventing the drain 18 side from creating an electrically floating state;
For example, do not connect resistors.

The same applies to the following examples.

FIG. 6 shows another embodiment of the invention. this is,
The drain 18 side of the MOS transistor 10
It is connected to the n-type base of a pnp-type bipolar transistor 40, the p-type emitter is connected to a power source 42 which is a reference voltage supply source, and the collector is connected to a load 43. The output end 44 is placed on the collector side.

FIG. 7 shows a voltage waveform 51 applied to the gate electrode 19 and a signal waveform 52 appearing at the output terminal 44 in this embodiment. The solid line indicates when there is no signal charge,
A broken line indicates the case where there is a signal charge.

When the voltage on the drain 18 side rises above the reference voltage due to the positive voltage pulse applied to the gate electrode 19, the junction between the base of the bipolar transistor 40 and the emitter of the reference voltage becomes reverse biased, and the bipolar transistor 40 becomes reverse biased. No current flows through 40. Then, when the voltage pulse is removed, as in the case of the previous embodiment, if there is no signal charge, the voltage on the drain 18 side simply returns to its original state, and no current flows between the base and emitter of the bipolar transistor 40. There is no change in the voltage at the output terminal 44. A current corresponding to the signal charge flows between the base and emitter of the bipolar transistor 40 only when there is a signal charge. At this time, due to the amplification effect of the bipolar transistor 40, the above current is applied between the emitter and collector of the bipolar transistor 40.
A large current multiplied by the amplification factor flows, and the output terminal 44
A large output signal 55 appears with inverted polarity. Needless to say, no signal due to switch noise appears.

FIG. 8 shows another embodiment of the present invention. A diode 60 is connected to the drain 18 side of the MOS transistor 10 in the same manner as in the first embodiment, and the other end is connected to the base of a bipolar transistor 70 for amplification. The P side of the diode 60 has a higher resistance 73 than the emitter of the bipolar transistor 70.
The steady current flowing through keeps it at a slightly lower voltage than the power supply 72, providing a reference voltage source. The switch noise removal and amplification functions in the second embodiment are performed using a diode 60 and a bipolar transistor 7.
0, and a signal similar to that of the previous embodiment is obtained from the output terminal 74. By adding the high resistance 73, the operating conditions of the bipolar transistor 70 can be made more favorable.

(6) Effects As explained above, according to the present invention, it becomes possible to extract only the signal component from a signal with large switch noise very easily.

Although the case has been described in which the voltage change caused by the amount of signal charge on the drain side of the MOS transistor is smaller than the voltage change caused by switch noise, only the signal component can be similarly extracted in the opposite case. In this case, the signal also appears when applying a positive voltage pulse to the gate electrode.

In addition, in the first and third embodiments, a diode was used to separate the signal and switching noise, but
A special example is a diode such as a backward diode that uses tunneling current.
You may use this. In this case, the direction of bonding is naturally reversed. In short, it is sufficient to connect the junction in series and directly to the drain side so that the junction is in the forward direction with respect to the signal charge.

Further, even when a junction field effect transistor is used (although I can't find any examples of this), problems similar to those of MOS transistors occur. The present invention has exactly the same effect in this case as well.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a MOS transistor, Figure 2
Figures 4 and 3 are explanatory diagrams of the prior art, and Figures 4 to 8
The figure is an explanatory diagram of an embodiment of the present invention.

Claims (1)

[Claims] 1. In a signal detection circuit of a device that uses a field effect transistor as a switch element to connect and disconnect a signal line, a signal charge is connected in series between the reference voltage supply source that applies a reference voltage to the drain of the field effect transistor and the drain. In contrast, the signal detection circuit is characterized in that the signal on the signal line is detected by connecting the junction as far as possible in the forward direction, applying a gate voltage to the field effect transistor and then removing it.