JPS6210918A - Pulse generating circuit - Google Patents

Abstract

PURPOSE:To attain start of pulse oscillation only with application of a power supply even when variation exists in characteristics between FETs by providing an active load field effect transistor (FETs) and the 1st resistor connected in parallel. CONSTITUTION:A couple of inverters comprising the active load FETs 13, 14 connected in parallel and a FET using the 1st resistors 19, 20 as loads a couple of capacitors 15, 16 connecting mutulaly input and output terminals of the inverters, and the 2nd resistors 17, 18 connected between the input terminal of each inverter and a constant potential are provided. Since the current saturation characteristic of the load of the inverters slows down by the 1st resistors 19, 20, the input input voltage range having >=1 voltage gain is widened. Thus, even when variation exists in the characteristic of each FET, positive feedback is applied by the application of power supply only and the pulse oscillation is started automatically.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a pulse generation circuit that can be used for digital signal processing and the like.

2. Description of the Related Art In recent years, pulse generation circuits have been used for clock signal generation in digital signal processing systems, and since they are built into MO8 type integrated circuits, field effect transistors (
Hereinafter referred to as rFETJ) is used! 1 is required.

Hereinafter, such a conventional pulse generating circuit will be explained using FIG. 4. FIG. 4 is a circuit diagram of an astable multivibrator which is a conventional pulse generating circuit, and 2 is an N-channel switching FET having a negative threshold voltage, which repeats switching alternately. 3.4 is a switching FET, and 2 is an active load transistor serving as a load, which is composed of FETs. 5 and 6 are capacities,
7 and 8 are resistors that form a delay circuit and determine the oscillation frequency of the astable multivibrator.

Next, the operation will be explained. First, the switching FET 1 and the active load transistor 3, and the switching FET 2 and the active load transistor 4 together form an inverter.If we consider the gate terminal of the switching FET 2 as the input and the drain terminal as the output, we can see that the switching FET 1 and the active load transistor 3 have mutual input/output. is capacity 5,6
connected through. These two inverters have voltage gain, so if some noise occurs, =
2 - The noise is amplified and positive feedback is applied, so the capacitance 5,6
A pulse oscillation is generated which is determined by the time constant of the resistors 7 and 8.

Therefore, in order to start pulse oscillation just by turning on the power, it is necessary that the voltage gains of the two inverters be 1 or more when the gate potential of the switching FET 2 is zero.

Problems to be Solved by the Invention However, according to the above conventional configuration, since an active load with good current saturation characteristics is used, the range of gate potentials in which the voltage gain of the inverter is 1 or more is extremely narrow. If there are variations in characteristics between FETs, the voltage gain when the gate potential is zero becomes 1 or less, and pulse oscillation cannot be started simply by turning on the power.

The present invention solves the above-mentioned conventional drawbacks, and aims to provide a pulse generation circuit that can start pulse oscillation simply by turning on the power even if there are variations in characteristics between FETs. .

Means for Solving the Problems In order to solve the above-mentioned problems, the pulse generation circuit of the present invention consists of field effect transistors whose loads are an active load field effect transistor and a first resistor connected in parallel with each other. a pair of inverters, a pair of capacitors connecting the input terminals and output terminals of these inverters to each other, and a second capacitor connected between the input terminal of each inverter and a constant potential.
The structure has a resistance of .

Effects According to the above configuration, the current saturation characteristic of the load of the inverter is made gentle by the first resistor, so that the input voltage range in which the voltage gain is 1 or more can be widened. Therefore, even if there are variations in the characteristics of each FET, positive feedback is applied just by turning on the power, and pulse oscillation is automatically started.

EXAMPLE Hereinafter, an example of the present invention will be described based on FIGS. 1 to 3.

FIG. 1 is a circuit diagram of an astable multivibrator which is a pulse generation circuit in an embodiment of the present invention, and 11 and 12 are N-channel switching FEs having negative thresholds.
T, 13.14 is an active load transistor consisting of an FET, 15.16 is a capacitance, and 17.18 is a resistance, which are the same as the conventional configuration shown in FIG. 19.20
is a resistor connected in parallel with the active load transistors 13 and 14 to moderate the current saturation characteristics of the load.

Next, the operation will be explained. First, to explain the input/output characteristics of the inverter, FIG.
A) is a conventional FET active load, (B) is a resistive load, (C
) respectively show the load curves in this example.

Figure 3 is an explanatory diagram of the input/output characteristics of the inverter, (D) (
E) and (F) respectively show the input/output characteristics of the FET active load, resistive load, and this example. When using a FET active load, the output voltage changes rapidly and a large voltage gain can be achieved, but as shown in Figure 2, when variations occur in the FET characteristics and active load current, the input/output characteristics shift left and right. , the voltage gain becomes less than 1 when the input voltage is zero, and self-oscillation does not start just by turning on the power. Further, with a resistive load, a large gain cannot be obtained, and if the resistance is too small, the gain will be less than 1, resulting in the same result. In this example, the current saturation of the FET active load is made gentle by the resistor, so the input/output characteristics of the inverter are such that the input voltage range can be controlled while maintaining the voltage gain, as shown by (F) in Figure 3. Since it can be made wider, it is possible to construct a pulse oscillation circuit that reliably generates oscillation even if there are variations in elements.

Effects of the Invention As described above, according to the present invention, a resistor is provided in parallel with the active load as the load of the astable multivibrator circuit composed of FETs, so even if there are variations in the elements, the power can be turned on without fail. can start self-oscillation.

[Brief explanation of drawings]

Figure 1 is a circuit diagram of an astable multivibrator as a pulse generation circuit in one embodiment of the present invention, and Figure 2 is a circuit diagram of an FE.
FIG. 3 is an explanatory diagram of the relationship between T and load, FIG. 3 is an explanatory diagram of the input/output characteristics of an inverter, and FIG. 4 is a circuit diagram of an astable multivibrator as a conventional pulse generating circuit. 11, 12... switching FET, 13.14.
...Active load transistor, 15.16...Capacity, 1
7-20...Resistance agent Yoshihiro Morimoto Figure 1 ti, tz-11 SWINASIG FET t7. History - @ 177゜Figure 2 Source P'L〉M voltage

Claims (1)

[Claims] 1. A pair of inverters consisting of a field effect transistor whose load is an active load field effect transistor and a first resistor connected in parallel to each other, and a pair of capacitors that interconnect the input terminal and output terminal of these inverters. and a second resistor connected between the input terminal of each of the inverters and a constant potential.