JPS60254935A - Method and device for analog multiplexing - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of the Invention The present invention relates to an analog signal multiplexing method and apparatus, and more particularly, when a relatively high power supply impedance is coupled to the multiplexer, The present invention relates to a multiplexing system that minimizes crosstalk.

(B) Description of the Prior Art Analog signals for multiplexing are generally input to the input terminal of a multiplexer via an active filter. These active filters typically include an operational amplifier with a low output impedance that increases the output voltage charge when the multiplexer switch closes and the charge is transferred to the multiplexer's output capacitance. Restrict. Minimizing this accumulated charge reduces crosstalk between channels, thus increasing the accuracy of multi-channel signals. Although inexpensive operational amplifiers are commonly used, the large number required makes them expensive. Additionally, amplifiers add weight to the multiplexer, occupy significant space on the circuit board, require assembly and test time, contribute to multiplexer failure rates, consume extra power, and are slow to react. it takes time.

Replacing the active filter with a passive filter significantly reduces the cost of the multiplexer, requires less space and weight, reduces assembly and test time, saves power, and increases the reliability of the multiplexer. . However, by using a passive filter,
The power supply resistance coupled to the input terminals of the multiplexer is increased, thus giving the charge stored on the output capacitor an opportunity to act on the input voltage during channel coupling. The charge accumulated on the signals of the channels that are in momentary contact during the previous channel coupling period constitutes inter-channel crosstalk, which adversely affects the accuracy of the multi-channel signal. Therefore, the capacitance at the output terminal of the multiplexer substantially reduces the charge accumulated during the previous channel coupling period, or the like, which is achieved before coupling the multiplexer output terminal to the next input channel. It would be desirable to provide a multiplexing system that utilizes passive filters.

e9 Arrangement of the Invention According to the principles of the invention, each input terminal of a multiplexer is coupled to a signal source via a passive filter, while its output terminal is coupled via a switch operated in conjunction with the sequential operation of the multiplexer. and connected to ground. Before coupling the input channels to the output terminals of the multiplexer, the full coupling switch wires of the multiplexer are opened and
Allowing the output terminal capacitance to be discharged through an energized switch coupled to the output terminal. After the output capacitance is discharged, the switch to ground is opened and the next coupling switch in the switch sequence is closed to provide the next signal in the sequence to the multiplexer output terminal. This order of operation is determined by the preceding multiplexed signal.
Removes residual signal accumulated on the output capacitance, thus significantly reducing inter-channel crosstalk.

DESCRIPTION OF THE EMBODIMENTS In FIG.
2 through multiple filters such as V, 8. and ■
It is coupled to a series of power supplies denoted s1. Combining switches such as switches 13, 14 and 15 sequentially couple the input terminal of the multiplexer 10 to its output terminal 16 and thus the signal sources to the output terminal 16 sequentially.

Before coupling the next input terminal in the sequence to the output terminal 16, the coupling switches 13, 14 and 15 are placed in the open position by the controller 17, which then energizes the switch 18 to connect the output terminal 16 to provide a path to ground. The controller 17 maintains the coupling switch in the open position and the grounding switch 18 in the closed position for a sufficient time interval so that the capacitor can be discharged at the output terminal 16 and thus approximately at ground potential level. A voltage is set at the output terminal 16. At the end of this period, switch 18 is opened and the next coupling switch 13 , 14 and 15 in the sequence is closed, coupling its corresponding signal source to output terminal 16 .

When the time interval for coupling this signal to the output terminal 16 ends, the controller 17 couples the signal to the multiplexer 10 to open the full coupling switch therein, and couples the signal to the ground switch 18 to couple the signal to the output terminal 16. gives a path to ground for the , and the above grosses are repeated.

The passive filter that couples the signal source to the input terminal of the multiplexer 10 may be of the type with a single pole, such as the filter 11, or a more complex multi-section filter, such as the two-pole filter 12. It's okay. For ease of presentation, the operational analysis below considers only a single-pole filter 11, but the operational principles described are equally applicable to more complex input filters.

In FIG. 2A, elements equivalent to those in FIG. 1 have the same reference letters and numbers, and coupling switch 13 is shown in the open position. Switch 1 in the switch sequence
Due to the residual charge on the capacitor CL due to the signal coupled by the previous switch 3, a voltage .L appears at the output terminal 16. In this case, the total charge in the multiplexing system is equal to the charge on the filter capacitor cB and the charge on the output capacitor CL.

This total charge is given by equation (1) in Figure 2A.

When switch 13 is closed as shown in FIG. 2B, the charges on capacitors CB and CL are distributed to produce a voltage v1 at the output terminal.

The load resistor tag is very large so that the total charge of the system remains unchanged for a relatively long period of time and the voltage 1 can be determined from equation (2a). If VL is placed at ground potential in the manner described above, the voltage 1 given by equation (2b) is no longer a function of VL and crosstalk in the system is significantly reduced.

In the circuits of FIGS. 2A and 2B, switch 1
3 is closed, current flows only during the time period.

Since the switch is operated periodically, FIGS. 2A and 2
Switch of the circuit shown in figure B.

The average current per period, representing the charge transfer through Sochi,
That is, there is an AVT, where T is the time interval between switch actuations. Therefore, the voltage 1 for steady state operation is as shown in equation (3) of FIG. 2B. Equation (3) clearly shows that FIGS. 2A and 2B
The circuit shown operates as a voltage divider formed by resistor R8 and equivalent resistance RBQ, where RBQ is the product f (CB
+cL), where f is the frequency of the switch operation. Multiplexer combination switch 1
3.14 and 15, this voltage 1 is subsequently coupled to the output terminal 16 for the input signal corresponding to each switch.

Although preferred embodiments of the invention have been described, the terminology used is intended to be descriptive, not limiting, and may depart from the true scope and spirit of the invention in its broader aspects. However, it should be understood that various modifications may be made within the scope of the claims.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a preferred embodiment of the invention, and FIGS. 2A and 2B are simplified diagrams of the coupling of input channels to the output terminals of multiplexers, which are useful in explaining the invention in detail. It's a circuit diagram. In the figure, 10 is a multiplexer, 11.12 is a filter,
13, 14, 15 and 18 are switches, and 17 is a control device, respectively. 11107-vscs+ VLCL FIG, 2A.

Claims (3)

[Claims] (1) A multiplexing method for minimizing inter-channel crosstalk in a multiplexing system, comprising: coupling a passive filter between a multiplexing signal source and an input terminal of a multiplexer; and connecting a passive filter between the multiplexer output terminal and ground. coupling a ground switch to the ground so that the output terminal is switchably grounded to the ground; providing a signal to the multiplexer to open the full coupling switch; and the coupling switch of the multiplexer being opened to connect the ground to the ground. after operating the switch, applying a grounding signal to the grounding switch to connect the output terminal to ground; and after the grounding signal operates the grounding switch, sending the grounding switch signal at predetermined time intervals; providing a signal to decouple the output terminal from ground; and providing a signal to the multiplexer to energize the next one of the coupling switches in the sequence, the signal source corresponding to the one switch; said method, comprising the steps of: coupling to said output terminal. (2) a multiplexer having a plurality of input terminals and one output terminal; a plurality of passive filters correspondingly coupled to the plurality of input terminals; and a plurality of passive filters coupled to the output terminal and having a plurality of input terminals; an apparatus for discharging a capacitor at the output terminal before coupling a selected one of the output terminals to the output terminal. (3) An analog multiplexing system according to claim 2, characterized in that the passive filter is of a type having resistor and capacitor elements.