JPS5813030A - Analog switch device - Google Patents

Abstract

PURPOSE:To reduce variation in the on-resistance of a switch and to prevent the generation of distortion by using a depletion type transistor as one of two MOS type field effect transistors (FET) which constitute the switch. CONSTITUTION:To the substrate electrode B of an N channel depletion type MOSFET5, a lower negative voltage than the voltage of an input signal IN is applied. When a clock signal phi has a level H and its signal phi' has a level L, MOSFETs 2 and 5 both turn on. As the voltage of the input singal IN varies, the voltage between the source of the MOSFET5 and the substrate electrode also varies, but a negative voltage is applied previously to the substrate electrode B, so the MOSFET5 has less variation in on-resistance. Thus, the generation of the distortion of the switch composed of the MOSFETs 2 and 5 is prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an analog switch device using an MOa field effect transistor.

An analog switch device is a clock signal that controls this device. −z, its state is switched to the on (conducting) state or the off (non-conducting) state, and when it is in the on state, 1 input power information, i.e.:: The analog input signal is transmitted to the output ′-; The device is such that no analog input signal is transmitted when it is in the off state.

FIG. 1 is a circuit diagram of a conventional analog switch device. This device is an N-channel enhancement type M
o8 g Field effect transistor (hereinafter abbreviated as MO8 transistor) 10 Enhancement type Mol! with source electrode B and P channel. ) Connect the drain electrode of transistor 2, and connect this connection point to the supply terminal S of the analog input signal IN, and also connect the above MO8) to the drain electrode of transistor 1.
Connect the drain electrode of Mo8) to the source electrode B of the transistor 20, and connect the connection point to the analada output signal OUT.
Furthermore, the f-) electrode GK of the MO8) transistor 1 is connected to the output terminal 4 of the MO8), and the electrode GK of the MO8)
) Transistor 2, f-) Electrode G is supplied with black and red signals i, which are a complementary pair with black and red signals φ, respectively, and N
A voltage Vll (corresponding to the low potential of the clock signal φ,i) is applied to the substrate electrode B of the channel Mo8) run raster 10.
For example, if the negative polarity voltage of the P channel is
o8) On the substrate electrode 11 of transistor 2: “□
Voltage VDD corresponding to the high potential of clock signal φ, ″i
(for example, positive polarity voltage), the signal φ is set to H level VDDs, the clock signal i is set to L level Vl
When both MO8) transistors 1 and 2 of the N-channel and P-channel are set to 1, their respective resistances RN and Rp become small. The output signal OUT is transmitted through the terminals 4 and 2, and the output signal OUT is taken out from the terminals 4 and 5. On the other hand, the clock signal φ is set to L level, and the clock signal φ is set to the L level.
When set to level □, both MO8) Lanzostar 1゜2 are turned off and their resistance Rx t RP
If ti is extremely large, the input signal IN will not be transmitted to the terminal 4'' and the output signal OUT will not be taken out.

By the way, in an analog switch device, the input signal IN is M
o8) It is necessary to make the voltage of the output signal OUT equal to the voltage of the input signal IN, or to make it proportional to the linear IMK, even if the output signal OUT passes through 2, and for this purpose, both MO8
) It is necessary to always keep the resistance value between terminals 3 and 4 constant when Lanzostars I and 2 are turned on. However, in the conventional analog switch device, the resistance between the terminals 3 and 4 changes according to the voltage at the terminals 3 or 4. This is a source group for Mo8) 7 resistors! There is a bias effect (pack r-bias effect), and this effect changes the threshold value of the Mo8) transistor.
This is because the on-resistance of the Mo8 transistor is affected by K. That is, an expanded proportional equation holds true for the on-resistance R of the Mo8 transistor.

Van: Bias voltage between the boot electrode and the source electrode, and Mo8) The threshold value Vth of the transistor is calculated by the following formula %
(Formula %) (2) vtho: Intrinsic threshold (when the bias voltage between the source electrode and the substrate electrode is Ov) tox: Thickness of the boot oxide film g, x: f) Dielectric constant εsI of the oxide film : Dielectric constant q of silicon : Amount of electron charge N : Substrate impurity concentration v■ : Bias voltage between the source electrode and substrate electrode φr : Fern level As is clear from equation (2) above, if Kv■ increases, The threshold value Vth also becomes large, and as Vth becomes large, R becomes large according to the above-mentioned equation (1).

Furthermore, the N-channel M08 transistor 1 of the analog switch device shown in FIG.
! A P channel MO transistor 2 is installed in a P channel region 12 formed by a diffusion method or the like in a semiconductor substrate 11, and a P channel MO8'
1, the impurity concentration of the P-well region 12 is naturally higher than that of the substrate 11, so that the sensitivity to the source-substrate bias effect of the threshold voltage of the N-channel MOB transistor 1 is higher than that of the P-channel MOB transistor 1. MO5! ) The price of Lanzosta 2 is also high, and it is usually about 3 times as expensive.

Therefore, when both MOB) transistors 1.2 are on,
When the voltage of the input signal IN applied to the terminal S is changed from Vll (Ov) to vDD (+5v)t, as shown in the characteristic diagram of Fig. 3, the resistance R of the MOB transistor l
, and the resistance R of MOB) 9 resistor 2 are not symmetrical, and as a result, the input (hi at the No. 8 INO intermediate voltage:
s'Voo (+2.5V) - In the past, the resistance between the input and output terminals is not constant, so the output Signal OUTK has the disadvantage that large distortion occurs.

By the way, the saw pre-substrate bias of the formula (2) is 5'.

(4) That is, it can be seen that if v■ is an extremely large value, the rate of change in ΔVth is small and ΔVth itself becomes saturated.

This invention was made in consideration of the above-mentioned circumstances, and its purpose is to apply the source-substrate bias effect to the MO8ml08ml field effect transistor pole by changing the analog signal voltage in advance. By supplying a sufficiently large bias voltage to give the above transistor a source-substrate bias effect exceeding The present invention provides an analog switch device that can obtain an output signal with less distortion.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 4 is a circuit diagram of the analog switch and slave device according to the present invention. In this device, an enhancement type MOB is used in the N f channel. Star 1. This MOB was replaced with an N-channel, degree, and N-type MOB ) Langistaro.
The substrate electrode BK is designed to supply a bias voltage V, which is a voltage (negative polarity voltage) even lower than the lowest voltage of the input signal IN, and the above-mentioned 11108)
The transistor 5 is provided in a P well region formed by diffusion or the like in an Nxl semiconductor substrate, as in the conventional case.
ing.

In the analog switch device having the above configuration, first,
Clock signal 9 φ is at L level and black.

When the signals are set to the 1t-II level, the N-channel dipleg and N-type MOBs are generated. The threshold value VthN of the second transistor 5 changes from a negative value to a positive value due to the north-substrate bias effect. Therefore, at this time, the N-channel M08 transistor Ad is turned off and its resistance R)1 is extremely large. value. On the other hand, since the black and red signals φ are at H level, the P-channel MOB
The resistance R of the transistor 2 also has an extremely large value, and as a result, the input signal IN is not transmitted to the terminal 4 and the output signal OUT is not taken out.

Next, the clock signal φ is set to H level, and the clock signal i is set to H level. input signal I at this time.
It is assumed that the voltage of N changes in the range from Ov to +5v. Source due to voltage change of input signal IN
N-channel Mo8 is more susceptible to substrate bias effects
) Since the substrate electrode B of the transistor 6 is supplied with a negative bias voltage vs in advance, the source-substrate/4 bias effect applied to the transistor 5 is caused by a change in the voltage of the input signal IN. 1 can be reduced to 5 with almost no change.

Therefore, there is no fluctuation in the threshold value of the transistor 5 (B10g), and the influence of threshold fluctuations in the on-resistance can be almost eliminated.

Figure 5 shows the intrinsic threshold value vthM of the N-channel Mo8 transistor 5 -2.5V, and the intrinsic threshold value vthP of the P-channel Mo8 transistor 2 -1.0V%.
MO8) The bias voltage vn supplied to the substrate electrode B of the range meta 50 is -5V, and both MOB) range transistors 5.
The voltage of the input signal IN applied to terminal JK when 2 is on is Ov
Resistance R of Mo8) transistor i and resistance RP% of Mo8) transistor 2 when changed from to +5V
and.

RN and R? This figure shows the characteristics of the resistance RO)I between terminals 3 and 4, which is expressed as a parallel resistance. In the characteristic diagram of the conventional device shown in FIG. 3, jVth of the N-channel Mo8 transistor increases when the voltage of the input signal IN is around +2.5V, and the value of R changes greatly. In the device, as shown in Figure 5, RH and R
, indicates that the potential of the input signal IN changes in a line-symmetric manner around +2.5V. That is,
This is an N-channel MOB) By supplying a bias voltage v1 to the substrate electrode l of the transistor 5 in advance, a source-substrate bias effect that exceeds the source-substrate ΔIas effect caused by the voltage change of the input signal IN is given to the Mo8 transistor 5. This is because changes due to changes in the threshold value of BM are minimized. Therefore, terminals 3, 4
The resistance between the input signal I and I has a nearly flat characteristic.
It is not affected by the voltage of N and can be set to a constant value.

As a result, distortion generated in the output signal OUT can be extremely reduced.

Note that the present invention is not limited to the above-mentioned embodiment. For example, in the above-mentioned embodiment, the source electrode 8 of the Mo8) las resistor 5 and the drain electrode of the Mo8) las resistor 2 are connected, and this connection point The input signal supply terminal 3
9 MO8) 5 Drain electrode D of Inzostar 6,! : Mo8) The case where the source electrode 8 of the transistor 2 is connected and the ζO connection point is connected to the output signal range output terminal 4 has been described. may be used as an output signal range output terminal.

In the above embodiment, an N-channel kID8) transistor is provided in a P-well region formed in the semiconductor substrate by a diffusion method, a P-channel Mo8) transistor is provided in the N-type semiconductor substrate, and the We have explained the case where a bias voltage vl is supplied to the O substrate electrode of a channel M08 transistor, but this is a case in which a P channel transistor is formed in a pH semiconductor substrate by a diffusion method or the like, a P channel transistor is provided in a 9N well region, and P′m When an N-channel Mo8) transistor is provided in a semiconductor substrate, the sensitivity of the threshold value of the P-channel Mo8) transistor to the source-substrate bias effect is greater than that of the N-channel Mo8) transistor. In the case of 0M, this P-channel 0M is applied to the substrate electrode of the P-channel Mo8 transistor due to the voltage change of the input signal IN.
A bias voltage Vm that provides a source-substrate bias effect that exceeds the source-1 plate bias effect applied to the O8 transistor (for example, input signal I
5 V (7), a voltage of +5 V or more may be supplied.

Further, when the impurity concentration of the substrates of the N-channel MOS transistor and the P-channel MOS transistor is high, each bias voltage as described above may be supplied to the respective substrate electrodes.

As explained above, according to the present invention, the bias voltage that gives the transistor a source-substrate bias effect that exceeds the source-substrate bias effect given to the MO8 type field effect transistor is determined by the analog signal voltage. Since the signal is supplied to the substrate electrode, it is possible to provide an analog switch device in which distortion occurring in the output signal can be extremely reduced.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of a circuit 11 of a conventional analog switch device, FIG. 2 is a cross-sectional view of the structure of an MOa field effect transistor constituting the device, and FIG. 3 is a characteristic diagram of the conventional device.
FIG. 4 shows one embodiment of this invention. 1...N-channel enhancement type MO8 type field effect transistor, 2...P channel enhancement type MO8111 field effect transistor, 3...
- Input signal supply terminal, 4 - Output signal output terminal, 5... N-channel degradation type MO8 field effect transistor, 11 - N-type semiconductor substrate, 12
-...P well region. Applicant's agent Patent attorney Takehiko Suzue ■ Figure 1, Figure 21! ! I *3B 1N(V)

Claims (3)

[Claims] (1) A source electrode and a drain electrode for inputting or outputting an analog-pda signal to a MOS m field effect transistor, and a control signal for controlling conduction of this transistor are input. A source F electrode and a substrate electrode are provided on the substrate electrode of the transistor so that the source-substrate bias effect imparted to the transistor due to the change in the analog signal voltage is reduced to a level where the change in threshold value due to the source-substrate bias effect is small. An analog switch device characterized in that, by using the transistor in the region, a change in the resistance of the transistor with respect to a voltage change of the input analog signal can be minimized, thereby minimizing distortion of the output analog signal. (2) The first channel of the first channel provided in the semiconductor substrate
a second MO of a second channel provided in an island region formed in the substrate and having an impurity concentration higher than that of the substrate;
B-type field effect transistor; The signal transmission electrodes of the second MOB field effect transistors are connected so that both transistors are connected in parallel, and each electrode connection point of both transistors is used as an analog signal input terminal or an analog signal output terminal, and the above-mentioned A substrate electrode of the second MOS m field effect transistor is provided in the island region, and a source-substrate bias effect is given to the MOS fi field effect transistor of the ji2 by a signal voltage change at the analog signal input terminal or the analog signal terminal. A bias voltage is supplied to the substrate electrode to provide the second MO8 field effect transistor with a source-substrate bias effect exceeding An analog switch device characterized in that it is configured to minimize resistance change and minimize distortion of an output analog signal. (3) The first MO8m field effect transistor is a P-channel enhancement type transistor, and the second M08m field effect transistor is a P-channel enhancement type transistor.
3. The analog switch device according to claim 2, wherein the O8 type field effect transistor is N-channel and manufactured by Deprezi Ren.