JPS622835Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a multiplexer drive circuit.

A conventional example of a multiplexer using a field effect transistor (hereinafter referred to as FET) as a switch element is shown in FIG. In FIG. 1, Q ₁₁ , Q ₂₁ , . . . Q _o1 represent a plurality of signals e ₁ , e ₂ , .
These FETs are respectively provided in series in the paths of e _o , and are driven by drive circuits consisting of transistors Q ₁₂ , Q ₂₂ , ...Q _o2 and inverters I ₁ , I ₂ , ... I _o , respectively. The signal path is designed to be intermittent. Each FETQi ₁ (i=1~n)
is of the depletion type, its gate is connected to the source by a resistor Ri ₁ , and
It is connected to the output end of each drive circuit through a parallel circuit of a diode D _i and a capacitor C _i . The drive circuit consists of an open collector type inverter I _i and a transistor Qi ₂ connected in cascade, and by turning on the previous stage inverter I _i by a multiplexer control signal, the transistor Qi ₂ is turned on. The collector potential, which had been on the voltage _V2 side and forward biased the diode D _i , is shifted to the opposite voltage _V1 side, thereby reverse biasing the diode D _i . FETQi ₁ is a depletion type, so
Depending on the order and reverse of the bias of the diode D _i , it is turned off and on, respectively. Each drive circuit operates sequentially at a predetermined timing to drive each FET.
Turn on one at a time.

In such a conventional multiplexer, the transistor Qi ₂ of the drive circuit is driven to saturation and performs a switching operation, so high-speed multiplexing cannot be performed due to its storage. One of the countermeasures is the transistor Q
It is possible to combine _i22 with a separate transistor for storage absorption, but transistor Q
Since there are the same number of _i22 as the number of signal points of the multiplexer, the same number of storage absorption transistors to be combined with them are also required, which is not economical.

Additionally, the circuit shown in Figure 1 has the disadvantage that if multiple transistors are turned on at the same time due to a failure in the drive circuit, the current consumption of the drive circuit increases in proportion to the number of transistors turned on, resulting in an increase in power loss. There is.

An object of the present invention is to provide a multiplexer drive circuit that has a simple circuit configuration and achieves high-speed multiplexing and prevents increase in power loss when turned on simultaneously.

In this invention, a common emitter resistor is provided at the emitters of the transistors in all the drive circuits, and by utilizing the negative feedback effect caused by the voltage drop of this emitter resistor, the transistors are operated at a constant current, and the power supply current when turned on at the same time is It is also designed to perform control.

Hereinafter, the present invention will be explained in detail with reference to the drawings.
FIG. 2 is an electrical connection diagram of the embodiment of the present invention.
In FIG. 2, parts similar to those in FIG. 1 are given the same symbols. The difference from Fig. 1 is that the emitter of the transistor Q _i22 of each drive circuit is connected to the application point of the power supply voltage V ₁ by a common resistor R ₂ , and the base of the transistor Q _i22 is It is connected to the dividing point of the output pull-up resistor of the inverter I _i in the previous stage.

In a circuit configured in this way, for example,
When the inverter _I1 of the first drive circuit is driven and turned on, the other end of its output pull-up resistor is connected to the common point, so that the divided value of the voltage _V1 is applied to the base of the transistor _Q12 as a bias voltage. given as. Therefore, transistor Q ₁₂ conducts and produces an output current, but due to the negative feedback effect due to the voltage drop across resistor R ₂ , equilibrium is reached at the point where the voltage drop across resistor R ₂ is approximately equal to the base bias voltage. , the output current is made constant. As this output current flows through the collector resistor and its voltage drop increases, diode _D1 is reverse biased, _FETQ11 is turned on, and a path for signal _e1 is opened.

Since the transistor _Q12 operates in an unsaturated state due to the negative feedback effect of the resistor _R2 , no storage effect occurs, and therefore high-speed multiplexing can be performed. The output transistors of other drive circuits also operate in a similar manner.

Since the resistor R ₂ is common to all transistors, even if multiple transistors are turned on at the same time for some reason, the sum of the currents of those transistors is
Since the value is the same as when only one transistor is conductive, power loss does not increase.

As described above, the present invention provides a common emitter resistor to the emitters of the transistors in all drive circuits, and utilizes the negative feedback effect due to the voltage drop of this emitter resistor to operate the transistors at a constant current and turn them on at the same time. It also limits the power supply current. Therefore, according to the present invention, with a simple circuit configuration, it is possible to realize a multiplexer drive circuit that achieves high-speed multiplexing and prevents increase in power loss when simultaneously turned on.

[Brief explanation of the drawing]

FIG. 1 is an electrical connection diagram of a conventional multiplexer, and FIG. 2 is an electrical connection diagram of an embodiment of the present invention. Q _i21 ... field effect transistor, Ri ₁ ... resistance,
D _i ... diode, C _i ... capacitor, Q _i22
...transistor, I _i ...inverter, R ₂ ...
resistance.

Claims (1)

[Scope of utility model registration request] A common resistor with one end connected to one terminal of the power supply, a plurality of voltage dividing resistors having one end connected to one terminal of the power supply, and a plurality of voltage dividing resistors provided in pairs with these voltage dividing resistors and operated according to a multiplexer control signal. A plurality of open collector inverters each having the other end of the voltage dividing resistor connected to a common point of the power supply voltage, and a pair of voltage dividing resistors provided in pairs with the plural voltage dividing resistors. A plurality of transistors each having a base connected to a voltage dividing point, an emitter connected to the other end of the common resistor, a collector connected to the other terminal of the power supply through each resistor, and outputting the potential of the collector as a multiplexer drive signal. Multiplexer drive circuit.