JP2000165217A - Changeover circuit for analog signal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a changeover circuit for an analog signal employing even an analog switch switched at a high-speed where an input output voltage is made stable with high precision. SOLUTION: A switching section for an analog signal having the analog switch 2 that has input channels CH1-CH4 of a plurality of analog signals S1-S4 and apply switch connection of the analog signals S1-S4 selectively to an output side A, a discharge circuit 3 that discharges charges stored in a capacitor C0 of the output side A of the analog switch 2 at the selection of the analog signals S1-S4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an analog signal switching circuit, and more particularly, to an analog signal switching circuit capable of stabilizing an input / output voltage in a switching circuit such as an analog switch.

[0002]

2. Description of the Related Art Conventionally, analog switches have been used to selectively connect a plurality of analog signals.
FIG. 8 shows an example of a conventional analog signal switching unit 10 using an analog switch.

In FIG. 8, reference numeral 2 denotes an analog switch having four inputs and one output, 4 denotes a buffer connected to the output side of the analog switch 2, and 5 denotes an AD converter which converts an analog signal output from the buffer 4 into a digital signal. , 6 are CPUs for outputting a control signal Sc for controlling the switching of the analog switch 2 and for inputting a digital signal from the AD converter 5. By periodically switching the internal switch Sw of the analog switch by the control signal Sc, the CPU 6 can sequentially AD-convert and input each of the analog signals S _{1 to} S ₄ .

That is, as described above, the analog switch
2 is used as the analog signal switching unit 10.
And four analyzers using one relatively expensive AD converter 5
Log signal S₁~ S_FourCan be converted to a digital signal.
Wear. Note that each analog signal S ₁~ S_FourIs the resistance R₁
~ R_FourAnd capacitor C₁~ C_FourBy low pass
Through each channel CH of the analog switch 2
1 to CH4 for high frequency noise generation
Minutes are removed in advance, and the analog
Signal S₁~ S_FourInstructions are stabilized.

[0005]

However, generally, there is some capacitance component C _{0 at} the output side of the analog switch 2, and the above-described conventional analog signal switching section 10.
In some cases, the influence of the capacitance component C ₀ may appear remarkably when the internal switch Sw is switched. That is, as shown in FIG. 9, for example, a voltage of the analog signals S ₁ inputted to the channel CH1 is greater than the voltage of the analog signal S ₂ to be input to the channel CH2, the internal switch Sw from the channel CH1 When switching to the channel CH2, a transient voltage fluctuation occurred at the output point A.

The waveform shown in FIG. 9 is output when the charge corresponding to the analog signal S ₁ is stored in the capacitor while the internal switch Sw selects the channel CH ₁ during the time T _{0 to} T _1. It is charged to C _0. Next, switch the internal switch Sw to the channel CH2 at time T _1, the charge stored in the capacitor C ₀ is charged in the capacitor C ₂ flows into the capacitor C _2.

The voltage output to the output point A is
Analog signal S_TwoOf the resistance R constituting the low-pass filter of FIG._Two
And capacitor C_TwoNext constant C_TwoR_TwoWhen determined by
Interval t ₁During this period, it changes transiently. That is, the internal switch
Time T at which Sw was switched₁For a certain period of time t₁Output during
The voltage generated at point A is input to channel CH2.
Log signal S_TwoIs different from the voltage of
Appears.

For this reason, the lower the cut-off frequency of the low-pass filter, the longer the time t ₁ becomes. For example, in the case of a low-pass filter attached to a sensor of a gas analyzer such as an automobile exhaust gas measuring device, A transient phenomenon of about 100 μs has occurred. Further, since the charge stored in the capacitor C ₀ is flowing back to the capacitor C ₂ of the input side, it was not also undesirable in terms of stability of the circuit on the input side of the analog signals S ₁ to S _4.

Usually, as a characteristic of the analog switch 2, when the voltage of the analog signal switched by the switching of the switch Sw becomes large, there is a characteristic that it can quickly follow the change. That is, it is conceivable that not only the capacitor C ₀ but also an internal circuit that can be equivalently represented by the diode D ₀ and the resistor R ₀ exists on the output side of the analog switch 2.

However, input to the analog switch 2
Analog signal S₁~ S_FourI know the size of
In any case, the period when the transient phenomenon occurs
Interval t ₁During the period, the AD converted data cannot be used.
won. And due to this problem, the analog switch 2
The switching speed cannot be increased beyond a certain speed.
Measurement changes fast, for example, according to the rotation of the engine
Analog signal S such as value₁~ S_FourCan not follow the input of
Had become a cause. Also, turn off analog switch 2.
When the replacement is performed at high speed, the input analog signal S
₁~ S_FourAccuracy may deteriorate depending on the magnitude of the voltage difference
There were inconveniences such as getting lost.

The present invention has been made in consideration of the above-mentioned circumstances, and provides an analog signal switching circuit capable of stabilizing an input / output voltage and achieving high precision even in an analog switch which can be switched at a high speed. It is intended to be.

[0012]

In order to achieve the above object, an analog signal switching circuit according to the present invention has a plurality of analog signal input channels, and selectively switches and connects each analog signal to an output side. In an analog signal switching section having an analog switch, a discharge circuit for discharging electric charges accumulated on an output side of the analog switch when the analog signal is switched is provided.

Therefore, by using the analog signal switching circuit of the present invention, the electric charge stored on the output side is discharged when the analog switch is switched, so that when the analog signal is switched, the analog signal in the state before switching is switched. You will not be affected at all. In general, an analog switch has a characteristic of responding at a high speed to a rising edge of an input voltage, and thus enables high-speed switching.

When one input channel of the analog switch is connected to a discharge potential point and this input channel is used as the discharge circuit, the circuit can be simplified and the production cost can be reduced accordingly. Can be.

[0015]

FIG. 1 is a diagram showing a configuration of an analog signal switching circuit 1 which is an example of the present invention. As shown in FIG. 1, an analog signal switching circuit 1 of the present embodiment has an analog switch 2 having, for example, four inputs and one output, and an output point A (connection side) of the analog switch 2 having a discharge potential point (hereinafter referred to as a common). And an analog switch 3 (discharge circuit) connected to G. The output point A of the analog switch 3 is connected to an AD converter 5 via a buffer 4, for example. 6 outputs control signals Sc ₁ and Sc ₂ for controlling the analog switches 2 and 3, respectively.
CP for inputting a digital signal output from the D converter 5
U.

In the following description of the specification, members denoted by the same reference numerals as those shown in FIGS. 8 and 9 are the same or equivalent members, and therefore, detailed description thereof will be omitted, and redundant description will be omitted. Avoid.

FIG. 2 shows an output waveform at an output point A of the analog signal switching circuit 1 shown in FIG.
It is a diagram showing a state of c _1, Sc _2. That is, first, during the period of time T _{0 to} T ₁ , the CPU 6
Its internal switches Sw1 and outputs a control signal Sc ₁ to be connected to the channel CH1, outputs a control signal Sc ₂ to the internal switch Sw2 to the open state with respect to the analog switch 3 against. At this time, the analog signal S
Charge corresponding to the _first voltage is charged in the capacitor C _0.

Next, during the period of time T _{1 to} T ₂ , the CPU 6
The after outputted a control signal Sc ₁ is the first analog switch 2 outputs disabled by the state (in FIG. 2 is being described as "OD"), any channel output point A is a state of not being selected , and it outputs a control signal Sc ₂ to the internal switch Sw2 of the analog switch 3 closed. At this time, the charge charged in the capacitor C ₀ is discharged, and the output voltage at the connection point A becomes 0 V (the same potential as the discharge potential point). The time t ₂ during which the analog switch 3 is in the closed state may be any time required for the potential at the connection point A to become 0 V.
In the case of 3, for example, it may be about 1 μs.

Next, at time T ₂ , the CPU 6 outputs a control signal Sc ₂ for switching the analog switch 3 to the open state, and then switches the internal switch Sw of the analog switch 2.
And it outputs the control signal Sc ₁ to switch 1 to the channel CH2. At this time, the potential at the connection point A, the analog signal S ₂ to be input to quickly channel CH2 at the same potential.

That is, the present invention provides an analog switch 2
When switching the internal switch Sw1 of, after disconnecting the old channel CH1, and, before switching to the new channel CH2, the charge stored in the capacitor C ₀ (the charge accumulated in the output side of the analog switch 2) By adding the discharging circuit 3 that discharges once and then switches to the new channel 2, switching can be performed at high speed without being affected by the analog signal of the previous channel when switching channels.

[0021] In the case of this example, from time T ₁ in which the channel switching after several μs can output a stable analog signal S _2, enable channel change by several tens of times faster when compared to conventional Can be In addition, since there is no influence of the previous channel, the accuracy can be improved accordingly. That is, even in a part where the engine requires high speed such as switching of the analog signals S _{1 to} S ₄ of the exhaust gas measuring device, reliable switching can be performed by using the analog signal switching circuit of the present invention. It is possible.

[0022] In the example described above, the control signal Sc ₂ of analog switch 3 constituting the control signal Sc ₁ and the discharging circuit 3 of the analog switches 2 are given directly from the CPU6, so to speak, the CPU6 analog Although an example of a control circuit for the switches 2 and 3 is shown, the present invention is not limited to this. For example, as shown in FIG. 3, the switching control signal Sc of the analog switch 2
And input control signals C ₁ ,
It may be provided separately control circuit 7 that generates a C _2.

FIG. 4 shows each control signal Sc based on the control signal Sc.
FIG. 3 is a diagram illustrating a method for generating ₁ and Sc ₂ . As shown in FIG. 4, the control circuit 7, when switching channels CH1~CH4 by the control signal Sc, only during a brief period t _2, to generate a control signal Sc ₂ for switching the analog switch 3 in the closed state, It is configured to generate a control signal Sc ₁ by inserting the output disenable period OD of slightly longer period including a period t ₂ with respect to the control signal Sc. By including such a control circuit 7 in the switching circuit 1 for analog signals, the switching circuit 1 for analog signals can be easily handled.

Further, in each example described above, an example of forming a capacitor C ₀ discharging circuit discharges the charge accumulated in the 3 'present at the output side of the analog switch 2 by the analog switch 3 However, the present invention is not limited to this, and can be variously modified.

FIG. 5 shows an example in which a transistor 8 is provided as a discharging circuit instead of the analog switch 3. Further, modifications such as using an FET in place of the transistor 8 can be easily performed. In other words, by using these transistors 8 (including FETs) in place of the analog switches 3, the configuration of the analog signal switching circuit 1 can be made simpler and faster, and the production cost can be reduced accordingly. be able to. Further, instead of the transistor 8 (including the FET), a photo MOS relay or an electromagnetic relay can be used.

FIGS. 6 and 7 show another modification of the present invention. As shown in FIG. 6, the analog signal switching circuit 1 of this embodiment uses the input channel CH5 in which the analog switch 2 is open, without using a separate analog switch 3 or other switching elements 8 or the like as a discharging circuit. A discharge circuit is formed. That is, by connecting the input channel CH5 to the discharge potential point G as shown in FIG. 7, when switching between the channels CH1 to CH4, a control signal S such that one end is connected to the channel CH5.
The c 'by outputting the analog switch 2, it is possible to discharge the charge accumulated in the capacitor C _0.
That is, the channel CH5 of the analog switch 2 forms the discharging circuit 3 ″.

In the case of this embodiment, the configuration of the analog signal switching circuit 1 can be further simplified, and the manufacturing cost can be reduced as much as possible. It is also possible to make a change such as providing a control circuit for converting the control signal Sc for controlling the analog switch to each of the channels CH1 to CH4 into the above-described control signal Sc ′.

In each of the above examples, the selected analog signals S _{1 to} S ₄ are input to the AD converter 5 and converted into digital signals. It is not limited. That is, the present invention can also be used when the selectively connected analog signals S _{1 to} S ₄ are switched and input to various analog arithmetic circuits at high speed. Needless to say, the number of analog signals input to the analog switch 2 is not limited.

Further, in each of the above examples, the example of the analog switch 2 which operates with a single power supply is shown. However, the present invention is not limited to this, and even if it operates with a power supply of ± 12 V, for example. It is feasible. In this case, the discharge potential point to which the discharge circuit is connected is not the common G, but
The negative power supply is -12V.

In addition, in each of the above descriptions, the equivalent circuit of the internal circuit on the output side of the analog switch 2 shown is taken into consideration from the characteristics thereof. It does not indicate that Therefore, in the claims of the present invention, the charge stored in the capacitor C ₀ in the equivalent circuit is expressed as “the charge stored on the output side of the analog switch”.

[0031]

As described above, according to the present invention,
When the analog switch is switched, it is possible to respond to the switch switching at a high speed without being affected by the analog signal in the state before the switching. Further, in the case where one input channel of the analog switch is connected to a discharge potential point and this input channel is used as the discharge circuit, the circuit can be simplified and the production cost can be reduced accordingly. it can.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an example of an analog signal switching circuit of the present invention.

FIG. 2 is a diagram illustrating the operation of the analog signal switching circuit.

FIG. 3 is a diagram showing a modified example of the analog signal switching circuit.

FIG. 4 is a diagram illustrating a control method of the analog signal switching circuit shown in FIG. 3;

FIG. 5 is a diagram showing another example of the analog signal switching circuit.

FIG. 6 is a diagram showing an example in which the analog signal switching circuit is simplified as much as possible.

FIG. 7 is a diagram illustrating a method of controlling the analog signal switching circuit shown in FIG. 6;

FIG. 8 is a diagram showing a configuration of a conventional analog signal switching unit.

FIG. 9 is a diagram showing the operation of the analog signal switching unit.

[Explanation of symbols]

1. Analog signal switching circuit 2: Analog switch
3, 3 ', 3'': discharge circuit, A: output side, CH1 to CH
4: input channel, G: discharge potential point, S _{1 to} S ₄ : analog signal.

Claims (2)

[Claims] 1. An analog signal switching section having an input channel for a plurality of analog signals and having an analog switch for selectively switching and connecting each analog signal to an output side. A switching circuit for an analog signal, comprising a discharging circuit for discharging a charge accumulated on a side of the analog signal. 2. The analog signal switching circuit according to claim 1, wherein one input channel of said analog switch is connected to a discharge potential point, and said input channel is used as said discharge circuit.