JPS60214629A - Analog signal selecting circuit - Google Patents

Abstract

PURPOSE:To transmit accurately a selected analog signal while removing the influence of a leak current when an analog switch is turned off by providing a leading-out means which leads another unselected analog signal to an earth side when the analog signal is selected. CONSTITUTION:For example, an ''H'' signal is applied to a control signal input terminal 41 and an ''L'' signal is supplied to a control signal input terminal 42. Then, a transistor (TR)72A turns on through a resistor 72B once an internal switch 11 is turned on, so an input terminal I2 of an analog multiplier 1 is clamped at the on voltage of the TR72A. A terminal 42, on the other hand, is at ''L'', so an internal switch 12 turns off and TR71A also turns on. When the terminal 41 is at ''L'' and the terminal 42 is at ''H'', on the other hand, the switch 11 is off, TR71A on, switch 12 on, and TR72A is off. Consequently, the leak current between the inut and output in the off state becomes extremely small and an offset voltage is not influenced by the input voltages.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention utilizes a conductor analog multiplexer to
The present invention relates to an analog signal selection circuit that can be used in a circuit that converts a plurality of analog signals into digital signals.

[Prior art]

Figure 3 is an example of [Troubleshooting for analog circuits, p. 25]
This is a conventional analog signal selection circuit shown in Figure 9.35 (OQ Publishing), in which (1) is an internal switch Qll, f that operates ON-OFF in response to a selection signal.
121-i5 built-in analog multiplexer, 12
1), gl is resistor t811. t321 indicates a data input terminal that applies an analog signal to the internal switch 011 (12). However, Ta), O 1
respectively close the internal switches αη and (121) to select an analog signal and connect the analog multiplexer (
1) is a control input terminal that outputs the analog signal from the analog multiplexer (1), and (5) is the analog signal output from the analog multiplexer (1).
This is a voltage follower circuit that sends out data to the D converter (6). Note that 1811.132) is a current limiting resistor.

An example of the operation of a conventional analog signal selection circuit having the above configuration will be described. For example, when selecting and outputting an analog signal applied to the data input terminal (21) from among the analog signals applied to the data input terminal (21) and the control signal input terminal, a high-level voltage selection signal is applied to the control signal input terminal. ) to the internal switch (11) via input terminal C. As a result, the internal switch (121) is closed and the analog signal applied to the data input terminal (21) is outputted to the output terminal 02 through the internal switch 01. Next, the analog 1h is connected to A via the voltage follower circuit (6).
/ D converter (6) and converted into a digital value. In the above example, since a low level voltage selection signal is applied to the control 1 input terminal decoy, the internal switch (1
2) is assumed to have been developed.

Next, when selecting the analog signal applied to the data input terminal (〃), the control signal input terminal t4i1
By switching + from high level voltage to low level voltage, and on the other hand switching control signal input terminal 1 from low level voltage to high level voltage, internal switch σ1) is opened and internal switch (12) is closed. The analog signal applied to the data input terminal 02 is outputted to the output terminal 02 via the internal switch 121, and is passed through the voltage follower circuit 5 to the A/D converter 02.
6) and converted into a digital value. In this way, analog signals are switched one by one from multiple analog signals based on the selection signal, outputted, and sequentially A/D.
Convert.

As mentioned above, when switching signals one by one from multiple analog signals and converting them into digital values sequentially, by providing an analog signal selection circuit consisting of an analog multiplexer in the front stage of the A/D converter (6), it is possible to convert multiple analog signals one by one. Even if it is a signal, a single A/Di converter (6) sequentially converts A /
D conversion becomes possible.

However, the analog multiplexer (1
), the internal switch Q"l + (12) is composed of a semiconductor, so for example, when the internal switch α1) is in an ON state, and on the other hand, the internal switch (121) is in an OFF state,
Even if the internal switch (121) is in the OFF state, a leakage current flows between the input and output of the internal switch (121), so that the analog signal on the internal switch α1 side may not be transmitted correctly.For example, when the data input When an analog signal of QV is applied to the terminal (21) and +IOV is applied to the data input terminal (2)), the internal switch 0 is ON, and the internal switch (with the support OFF and the resistor !81) is IOKΩ, Assuming that the leakage current of the internal switch (121) is 1 μA, in this case, the leakage current of the internal switch (Makoto's leakage current is 5- current is internal switch 01) - resistor (81) - data input terminal (211), and the current flows from resistor (81). 1μAX on both ends of
A voltage drop of IOKΩ=1QmV occurs. Therefore, a voltage of 1QmV is applied to the input of the voltage follower circuit (5) (hereinafter, the voltage generated by leakage current is referred to as an offset voltage). If the voltage is sufficiently high compared to the voltage, there is no need to consider it as a circuit error, but if the voltage is very small, it becomes a problem.

That is, in the above example, l is connected to the data input terminal (21).
When a voltage of QmV is applied, 10 mV in addition to the offset voltage is added to the input of the voltage follower circuit (5), and a voltage of 20 mV, which is approximately twice that, is applied to the input of the voltage follower circuit (5). If the pressure is constant, the offset can be easily corrected by processing after A/D conversion or by adding an offset correction circuit to the analog signal switching circuit.

However, the leakage current of an analog switch changes depending on the input voltage applied to the data input terminal, so when dealing with minute voltages in conventional circuits, it is difficult to accurately measure the leakage current unless offset correction is performed according to the voltage of each input. However, there was a problem in that analog signals could not be A/D converted.

[Summary of the invention]

SUMMARY OF THE INVENTION It is an object of the present invention to overcome the conventional drawbacks and to provide an analog signal selection circuit in which the offset voltage is reduced and the offset voltage is not affected by voltage values applied to other data input terminals.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. The same reference numerals as in Fig. 6 indicate the same - or equivalent parts. 0σ1) is the input signal clamp circuit of the data input terminal (D), the question is the input signal clamp circuit of the data input terminal (D), and this clamp circuit is , respectively transistor (71A), (
72A) and its pace resistor (71B).

(72B) and resistors (71c) and (72c) inserted between the base and emitter. Now, control signal input terminal 141)
It is assumed that %HII multiplied signal + voltage) is applied to the control signal input terminal 1, and a ゝゝL〃 signal (YOv) is applied to the control signal input terminal 马1. When XXH// is applied between the control signal input terminals, the internal switch (11) turns on and at the same time the resistor (72B
) because the transistor (72A) is turned on through
The input terminal (2) of the analog multiplexer (1) is clamped to the ON voltage (2□v) of the transistor (72A). On the other hand, the open side 1 signal input terminal (st L /
7, the internal switch (121) is turned OFF and the transistor (71A) is also turned OFF'.
The distance between the control signal input terminals is ゝゝL〃, the control signal input terminal□□
□(If SS H// is, switch (11) is OFF, contrary to the above), transistor (7+A) is ON, internal switch (Mausoleum is ON, transistor (72A) is OFF)
It becomes F.

That is, no matter what voltage is applied to the input terminal, the input voltage of the analog switch whose internal switch is OFF is always clamped to the ON voltage of the transistor. As a result, the leakage current between the input and output at the time of pOFF is extremely small, and the offset voltage is not affected by the input voltage.

Therefore, offset correction of the signal selection circuit can be eliminated. Also, the offset of the input signal itself, the offset of the voltage follower circuit (5), and the A/D converter (6)
Even if offset correction is required, including the offset of

In the above explanation, we have explained the case in which two people input the analog signal, but it goes without saying that the same effect can be obtained even in the case of n inputs.In addition, in this embodiment, it is assumed that a positive voltage is applied as the analog input voltage. do.

Next, referring to FIG. 2, another embodiment will be explained. (8
) is an input signal clamp circuit that uses an analog switch. Control signal input terminals C3, C4 and output terminals 0. of the analog switch (8). and 04 are analog codes → ÷
Control signal input terminal 02 of φ multiplexer (1). The analog switch (8) input terminal channels □ and 2 are connected to the input terminal channels □ and 2, respectively, and the input terminal channels of the analog switch (8) are grounded to the ground side. In other words, when the control signal input terminal becomes XVHI/, the internal switch (111) of the analog 9-log+multiplexer (1) turns on, and at the same time the internal switch (8) of the analog switch (8) turns on. The voltage at the input terminal CH of the multi-1 plexer (1) is clamped to the voltage determined by the ON resistance value of the resistor ('s4) and the switch ((to).On the other hand, the control signal input terminal KATO1 is connected to the SS H// When the internal switch (121) of the multiplexer (1) turns on, it is clamped to the voltage determined by the ON resistance value of the analog switch (light), and the same effect as in the embodiment shown in Fig. 1 is obtained. According to this embodiment, positive and negative voltages can be applied as analog inputs.

According to each of the above embodiments, 1. By clamping the inputs of analog switches other than the analog switches set to approximately Ov, it is possible to make the offset voltage due to leakage current when the analog switch is OFF extremely small, and to eliminate fluctuations in the offset voltage due to changes in input voltage. This has the effect of simplifying the offset correction circuit because the fluctuation in the amount of sheath is reduced. If multiple signals are selected due to a failure or malfunction of the selection signal generation circuit (not shown), all inputs become clamp voltages, which has the effect of making failure detection easier. [Effects of the Invention] As explained above. In particular, on the analog signal selection side M with an analog multiplexer, the analog signal selection is
By providing a deriving means for deriving other non-selected analog signals to the ground side, the influence of leakage current when the analog switch is OFF can be removed, and the selected analog signal can be accurately transmitted. In addition, if a plurality of signals are selected due to a failure or malfunction of a selection signal generation circuit (not shown), all inputs are led to the ground side, which facilitates failure detection.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing one embodiment of the analog selection circuit by Akira Fuko, Fig. 2 is a circuit diagram showing another embodiment of the present invention, and Fig. 6 is a circuit diagram showing a conventional analog signal selection (b) circuit. FIG. (1)...Analog multiplexer (71A), (72A)...Transistor (8)...
Analog Switch Note that in the figures, the same parts are indicated by the same symbols. Agent Masuo Oiwa Figure 3 procedural amendment (voluntary) 2. Name of the invention Analog signal selection circuit 3. Person making the amendment Relationship to the case Patent applicant address 2-2-3 Marunouchi, Chiyoda-ku, Tokyo Name Name
(601) Mitsubishi Electric Co., Ltd. Representative Hitoshi Katayama 4, Agent Address 2-2-3 Marunouchi, Chiyoda-ku, Tokyo Mitsubishi Electric Co., Ltd. Detailed description of the invention in the specification and drawings. 6. Contents of the amendment (1) The statement "However," on page 3, line 7 of the specification is amended to "and J." (2) "Current limiting resistor" on page 3, line 13 of the specification. The description "A resistor that simulates the output impedance of an analog signal source" is corrected. (3) “Internal switch (12)” on page 3, line 20 of the specification
The description J is corrected to ``internal switch (11) J.'' (4) The description ``output terminal 02'' on the second line of page 4 of the specification is corrected to ``output terminal oIJ.'' (5) The description ``output terminal oIJ'' is corrected to ``output terminal oIJ.'' Figure 1, Figure 2, and Figure 3 are corrected as shown in the attached sheet. 7. Attached document catalog drawings 1 copy or more

Claims (1)

[Claims] (1) In an analog signal selection circuit equipped with an analog multiplexer that selects one signal from a plurality of analog signals based on a selection signal, when an analog signal is selected, other unselected analog signals are routed to the ground side. An analog signal selection circuit comprising derivation means for deriving the signal. (2) The above derivation means is a clamp circuit including a transistor whose collector is directly connected to the input terminal of the analog multiplexer, whose emitter is grounded to the ground side, and whose base becomes conductive upon receiving another analog signal selection signal. are installed on each input side of the analog multiplexer, and when receiving a signal for selecting another analog signal, the above-mentioned transistor becomes conductive, thereby sending the non-selected analog signal applied to the collector of the transistor to the ground side. 2. The analog signal selection circuit according to claim 1, wherein the analog signal selection circuit is configured to derive the signal. (8) The deriving means is connected to an analog switch 151+, which has one end directly connected to the input terminal of the analog multiplexer, and the other end is grounded to the ground side, and receives another analog signal selection signal at the control signal input terminal; When the analog switch is installed at each input side of the analog multiplexer and receives another analog signal selection signal, only the analog switch that receives the signal closes, thereby eliminating the unselected analog signal applied to one end of the analog switch. 2. The analog signal selection circuit according to claim 1, wherein the analog signal selection circuit is configured to lead out the signal to the ground side.