JPS5941928A - Electronic switch - Google Patents

Abstract

PURPOSE:To improve a distortion characteristic and to extend the use range of switch, by constituting a circuit so that a well is connected to a signal path when the switch is turned on, and connecting a capacity element, which cancels the voltage dependence of p-n junction capacitance between the well and a substrate, between the well and a reference potential point. CONSTITUTION:An electronic switch circuit is provided with a circuit consisting of p type insulated gate FETs (MISTs) 1 and 2 and n type MISTs 3 and 4, and analog signal input and output terminals 8 and 9 and a switching signal input terminal 7 are connected to MISTs 1, 2, 3, and 4. MISTs 1 and 2 are formed in a p type semidonductor base material, and MISTs 3 and 4 are formed in an n type well formed in this base material. The circuit is so constituted that the well is connected to the signal path when the switch is turned on, and a disotortion suppressing capacity element 13 which cancels the voltage dependence of an pn parasitic capacitance 12 formed between the well and the semiconductor substrate and has the voltage dependence in the connection relation is connected between the well and a reference potential 11, thus improving the distortion characteristic.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application Inventively, an insulated gate field effect transistor (hereinafter abbreviated as MIST) formed integrally within a single semiconductor substrate. It relates to electronic switches that open and close passages for analog signals such as signals.

Conventional configuration and its problems As shown in Figure 1, a conventional electronic switch consisting of MISTs integrated into a single semiconductor substrate has p-channel MISTs 1 and 2, and n-channel MISTs. M: [S
A circuit in which T3+4+5 and inverter 6 are connected, terminal 7 is an input terminal for a switching signal that prevents the switch from closing, terminal 8 is an input terminal for an analog signal, and terminal 9 is an output terminal for an analog signal. The structure is as follows.

Note that 10 is a positive %JE (VDD) (7) application terminal, and 11 is a negative voltage (Was) application terminal. By the way, the conductivity types of the channels of MIST1, 2 and MIST3-5 are opposite, and MIST3.4 is placed in the same well, for example, a p-well, and MIST5 is placed in a different p-well.
Assuming that it is built in the well, MIST3
and 4 are formed between the p-well and the substrate.
A capacitance 12 due to the n-junction is present in the circuit in the relationship shown.

With the above circuit configuration and conventional electronic switch, MIST1 and 3 become a path for analog signals,
When MIST2 and 4 are on, the p-well, which is the back gate of MIST3, is connected to the analog signal input terminal, and the MIST
It functions to enhance the effect of canceling out the nonlinearity of the on-resistances of ST1 and ST3 with respect to the input bias. Furthermore, when MIST5 is off, the p-well, which is the back gate of MIST3, is connected to the negative voltage (Vss) terminal 11, which serves to reduce the decrease in feedthrough between input and output. By the way, since the p-well, which is the back gate of the MIST 3, is connected to the analog signal input terminal 8 when it is on, the p-n junction between the p-well and the n-type substrate is reverse biased. Therefore, the parasitic capacitance 12 caused by the pn junction
is where it exists. As is well known, this capacitance value depends on the voltage. Therefore, the capacitance value changes depending on the peaks and valleys of the input signal, and the impedance also changes. When the frequency of the input signal increases, the voltage of i is divided by the signal source impedance and the impedance of this parasitic capacitance 12, and the voltage division ratio changes between peaks and valleys of the input signal, causing distortion in the signal. . The input signal frequency dependence of distortion in a conventional electronic switch is shown by the curved line in FIG. In this example, the signal source impedance is 3.3Ω and the load impedance is 15Ω.

As explained above, in conventional electronic switches, it is impossible to prevent distortion caused by capacitance caused by the fabrication of small wells when the circuit is fabricated on a single semiconductor substrate. 1. OBJECTS OF THE INVENTION It is an object of the present invention to provide an electronic switch that suppresses distortion that is a problem in conventional electronic switches and improves distortion characteristics.

Structure of the Invention The electronic switch of the present invention is composed of a p-channel MIST and an n-channel MIST, and a well of one conductivity type in which one of the conduction channel type MISTs is formed serves as a signal path when the switch is turned on. A variable capacitance element having a basic configuration connected to the well and having a voltage dependence due to a connection relationship that cancels the voltage dependence of the pn junction capacitance formed between the well and the substrate. is connected between the well and a reference potential point, and this variable capacitance element is used to suppress distortion that becomes noticeable especially when the signal frequency is high.

DESCRIPTION OF EMBODIMENTS A second example of a circuit course regarding an uninvented electronic switch is shown below.
A detailed explanation will be given below with reference to the drawings and FIG. 4 showing an example of the structure of a variable capacitance element.

FIG. 2 is a diagram showing an embodiment of the electronic switch of the present invention, which differs from the conventional electronic switch shown in FIG. 1 only in the presence of a capacitive element 13, and other configurations. is the same as the configuration of a conventional electronic switch. However, the capacitive element 13 is added as a pn junction capacitor like the capacitive capacitor 12, but the conductivity type on the side connected to the back gate 1 of the MIS T3 gives the capacitive capacitor 12. The conductivity type of the well is opposite to that of the well. Next, the operation of the inventive electronic switch will be explained. Assuming that the conductivity type of the well is p-type, the parasitic capacitance 12 is p-type on the open gate side of MIST 3 and n-type on the positive voltage (Vnn) terminal 10 side, so the potential of analog human power 3 increases in the positive direction. Then, the potential difference between both ends of the capacitive capacitor 12 becomes small, and its capacitance increases. On the other hand, since the potential difference between both ends of the capacitive element 13 becomes small at this time, its capacitance decreases and acts to cancel out the increase in the capacitance of the parasitic capacitor 12. Therefore, the dependence of the signal source impedance and the voltage division ratio by these capacitances on the input voltage level is reduced, and therefore the occurrence of distortion is reduced. By fully optimizing the capacitance value of the capacitive element 13, a large canceling effect can be achieved.

Curve B in FIG. 3 shows the input signal frequency dependence of distortion in the electronic switch of the present invention constructed as described above. It is clear that there is a large kina canceling effect compared to curve A of the conventional electronic switch.

FIG. 4 is a diagram showing a specific example of the formation of the capacitive element 13 shown in FIG. 2, and has a structure in which the drain diffusion of the MIST 5 is expanded in the illustrated structure. That is, n-type silicon substrate 1
MIST 6 is formed in the p-well 16 for forming MIST 5 prepared in step 4.

A - type drain region 16 and a 1 type source region 17 are all formed for this purpose, and a capacitive element 13 is formed entirely by a pn junction formed between the n+ type drain region 16 and the p well 16. In addition, in the figure, 18 is an oxide film, 191Ml5T5
(7) a gate electrode, an electrode that also serves as the drain electrode of 20[1JIsT5 and the cathode electrode of the pn junction capacitor 13;
21iq is an electrode serving as the source electrode and back gate electrode of MIST5, and 22ta is an f-type guard band region. In this way, the MIST 5 also serves as the capacitive element 13 for distortion suppression, and by connecting the MIST 5 to the circuit 9 shown in FIG. 2, the connection between the bank gate of the MIST 2 and the negative voltage (Vss) terminal has a capacitive element 13
will be connected.

ADVANTAGEOUS EFFECTS OF THE INVENTION The electronic switch of the present invention enables the opening and closing of an analog signal path without causing distortion due to the addition of a capacitive element, and is highly effective in improving the performance of audio equipment. In addition, the distortion characteristics are improved up to the signal frequency range with high
This also has the effect of expanding the range of use of electronic switches.

In the example described above, the circuit is realized with an 0MO3 structure in which a p-well is formed in an n-type substrate, but on the contrary, it is realized as an 0MO8 structure in which an n-type well is entirely formed in a p-type substrate. The present invention can also be applied to the case of realizing a circuit, and the same effects as those described above can be obtained. In addition, capacitive element 1
According to the structure of the embodiment in which MIST 3 is integrally formed with one of the MISTs, the effect of increasing the utilization rate of the substrate area is achieved.
If this effect does not need to be particularly important, the capacitive element 13 may be built as an independent circuit element. Furthermore, the capacitive element 13 may be added as an MIS type variable capacitive element without being particular about the pn junction capacitance.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of a conventional electronic switch, Fig. 2 is a circuit diagram of an electronic switch according to the invention, and Fig. 3 shows the distortion characteristics of the conventional electronic switch circuit and the electronic switch of the invention. A comparative diagram, FIG. 4, is a diagram illustrating a configuration example of a capacitive element for suppressing distortion. 1.2...p channel MIST, 3-6...
... n-channel MIST16 ... inverter, 7 ... switching signal input terminal, 8 ... analog signal input terminal, 9 ... analog signal output terminal, 1o...Positive voltage (VDD) terminal, 11
...Negative voltage (Vss) terminal, 12...
・Parasitic appearance, 13...Capacitive element for distortion suppression, 1
4.°°°°°n-type silicon substrate, 15...p
Type well, 16...1 type drain region, 17.
....-type source region, 18... ... oxide film,
19...Gate electrode, 2o...Drain electrode (capacitive element electrode), 21...Source electrode (back gate electrode), 22...p++ guard band region. Name of agent: Patent attorney Toshio Nakao (1st person)
Figure 2

Claims (1)

[Claims] (1) Insulated gate type field effect with complementary polarity, in which the drain and source circuits are connected in parallel between the signal input terminal and the signal output terminal, and switching signals are applied to the gates in an opposite phase relationship. One of the transistors is formed in a semiconductor substrate of one conductivity type, and the other is formed in a well of an opposite conductivity type formed in the same semiconductor substrate, and the well is connected to a signal path when the switch is turned on. and a voltage-dependent capacitive element is connected between the well and the reference potential point in a connection relationship that cancels the voltage dependence of a pn junction capacitance formed between the well and the semiconductor substrate. Features an electronic switch. (The electronic switch according to claim 1, wherein the capacitive element is formed of a pn junction capacitor. (3) The capacitive element is formed of a capacitor of a metal-insulator-semiconductor structure. The electronic switch according to claim 1, characterized in that: (4) a pn junction between different wells and regions of opposite conductivity type in which capacitive elements are formed; An electronic switch according to claim 1, characterized in that it is formed of a capacitor.