JPS62610B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to current switched logic circuits, and more particularly to set-reset flip-flop circuits.

There are various types of circuits that process digital signals, but current-switching circuits are widely used when high speed is required. One of the circuits to be stored is a set/reset flip/flop circuit.

An example of a conventionally widely known current switching type set-reset flip-flop circuit is shown in FIG. This consists of a first transistor set (flip-flop circuit) for holding information, consisting of transistors 2 and 3 connected to one constant current source 1, and a second transistor set for writing information, consisting of transistors 4 and 5. a first and a second transistor set connected to a further current source (not shown).
It consists of level shift circuits 6 and 7 that shift the collector potential of the transistor set by a constant voltage and feed back the state to the first transistor set, and apply it to the second transistor set (base of transistor 4 or 5). The input signal threshold to be shifted is determined by the shifted potential, and some extra elements and power are required for the shift. Note that 8 and 9 are collector resistors, 10 and 11 are output terminals of the flip-flop circuit, and 12 is a constant voltage power supply terminal.

Another conventionally known example is shown in FIG. 2, which aims to reduce the number of elements and power consumption. In this case, a first transistor set for holding information consisting of transistors 2 and 3 and a second transistor set for writing information consisting of transistors 4 and 5 are connected in the same way as in the example shown in FIG. However, the circuit configuration is simple as it is fed back from the collector potential without going through a shift circuit, but the threshold of the input signal is determined by the collector potential, and in order to use the transistor only in the non-saturation region, This has the disadvantage that the input signal potential cannot be set high enough, resulting in reduced noise margin.

An object of the present invention is to provide a set/reset flip-flop circuit which fixes the input threshold voltage without increasing the number of elements or power consumption and has a large noise margin.

According to the present invention, a pair of switching elements each having a load connected in series are inserted in parallel between a power supply terminal and a constant current source, and each of the pair of switching elements is provided with means for feeding back the output of one to the input of the other. In the set/reset flip-flop circuit, the basic flip-flop circuit is constructed by connecting a pair of current switching type switches between the constant current source and the output of each switching element to enable setting and resetting. A set-reset flip-flop circuit characterized in that another switching element equipped with a control terminal to supply a predetermined reference potential is inserted in series between the flip-flop basic circuit and the constant current source. is obtained.

Next, the present invention will be described in detail with reference to Examples and drawings.

FIG. 3 is a circuit connection diagram showing an embodiment of the present invention, in which a transistor is used as a switching element. The emitter of the transistor 14 (the other switching element) is connected to the constant current source 1, and the base is connected to the reference voltage. The collectors are connected to the common emitters of transistors 2 and 3 for holding information, which constitute the flip-flop basic circuit, and the transistors 2 and 3 are connected to the common source (not shown).
The bases of 3 are connected to the collectors of transistors 3 and 2, respectively, and the collectors 15 and 16 are connected to resistors 8 and 2, respectively.
9 to the power supply 12, and also to the collectors of transistors 4 and 5 for writing information, the emitters of the transistors 4 and 5 are connected to the constant current source 1, and the bases each have a set voltage. A reset signal is input. now,
When the two input signals are both at low level, the current flowing through the constant current source 1 flows through the transistor 14, which has a higher base potential of the holding transistor group, for example, the transistor 2, and is further connected to the collector 15 of the transistor 2. The current flows from the power source 12 through the resistor 8. Therefore, the collector 15 is at a low level, and the transistor 3 to which this potential is applied to its base is in a non-conducting state, and its collector 16 is at a high level, so that a high level is applied to the base potential of the transistor 2. Transistor 2 remains conductive, ie, remains in its previous state. Next, when the input signal applied to the base of transistor 5 becomes higher than the reference voltage applied to the base of transistor 14, transistor 1
4 is cut off, the current from the constant current source 1 flows through the transistor 5, and when the potential at the collector 16 is brought to a low level by the resistor 9, at the same time, the potential at the collector 15 is brought to a high level. Here, when the input signal becomes low level again,
As mentioned above, the transistor 14 becomes conductive, but at this time, the base potential of the transistor 3 is at a higher level, so in the holding transistor group, the transistor 3 side becomes conductive, and the collector 16 potential remains at a low level, while the collector 15 remains at a high level. be. Furthermore, even if the input signal becomes high level again, the above-described operation is performed. Furthermore, with respect to the input signal applied to the base of transistor 4, the operation of the transistor group and the resistor group is exactly the same as described above for the input signal applied to the base of transistor 5, except that the operation of the transistor group and the resistor group is in opposite phase to that in the above case. Perform the following actions. Therefore, it operates as a set/reset flip-flop circuit with one of the two inputs serving as a set input and the other input serving as a reset input.

The conventional circuit example shown in FIGS. 1 and 2 also operates in substantially the same manner as in FIG. 3, except for the operation of the transistor 14.

However, the threshold value for the input signal is determined by the potential generated within the flip-flop in conventional circuits. That is, in the example of FIG. 1, the potential is determined by shifting the potential of the higher level of the outputs 10 or 11.In the example of FIG. 2, the potential is determined by the potential of the higher level of the outputs 10 or 11. It is determined by the potential of the reference voltage source applied to the base of the transistor 14, and therefore can be fixed at an appropriate value. To be precise, in all of the above examples, the threshold value will be slightly shifted due to the hysteresis characteristic, but this can be easily corrected by adjusting the potential of the reference voltage source.

In addition, in the example shown in Figure 2, if the high level of the voltage applied to the input side transistor is set higher than the high level that can be applied to the base of the holding transistor set, the collector potential will be lower than the base potential when the input side transistor set is conductive. If the voltage decreases too much, the transistor will enter the saturation region, impairing high-speed performance, and therefore the input signal level cannot be increased above a certain value. Therefore, a sufficient noise margin cannot be obtained. Furthermore, failure to set the input signal sufficiently above the threshold voltage may slow down the operating speed of the driven transistor. On the other hand, according to the present invention, by appropriately setting the potential of the reference voltage source to a value sufficiently lower than the potential that the collector of the input side transistor can take, the transistor can be operated in the non-saturation region and the noise can be suppressed to a sufficient level. The input signal level can be set with a certain margin.

As described above, according to the present invention, a stable threshold level can be achieved without increasing power consumption and only by adding one transistor (assuming that the reference voltage is drawn from other parts of the LSI), and the noise can be reduced. A high-speed set/reset flip-flop circuit with a large margin can be obtained.

[Brief explanation of the drawing]

Figure 1 shows the conventionally known set, reset,
FIG. 2 is a circuit connection diagram showing an example of a flip-flop circuit. FIG. 3 is a circuit connection diagram showing another conventional example, and FIG. 3 is a circuit connection diagram showing an embodiment of the present invention. In the figure, 1... Constant current source, 2, 3... Information holding transistor, 4, 5... Writing transistor, 6, 7... Level shift circuit, 8, 9... Collector load resistance, 10, 11 ... Flip-flop output terminal, 12 ... Constant voltage power supply terminal, 13
. . . Common load resistance, 14 . . . Input threshold level setting transistor, respectively.

Claims (1)

[Claims] 1. A pair of switching elements each having a load connected in series are inserted in parallel between a power supply terminal and a constant current source, and the pair of switching elements each have means for feeding back the output of one to the input of the other. A set/reset flip-flop circuit is provided, which constitutes a basic flip-flop circuit, and is capable of setting and resetting by connecting a pair of current switching type switches between the constant current source and the output of each switching element, A set-reset flip-flop characterized in that another switching element having a control terminal for supplying a predetermined reference potential is inserted in series between the flip-flop basic circuit and the constant current source. circuit. 2. The set/reset flip-flop circuit according to claim 1, wherein the switching element is a bipolar transistor.