JPH09307357A - Oscillation circuit for microcomputer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the current consumption of a microcomputer. SOLUTION: The oscillation circuit is constituted by using an inverter circuit 1 outside of the microcomputer 11. Thereby the current consumption of the inverter circuit 1 is reduced by inserting current limiting resistors 9 and 10 to the current path of the inverter circuit 1. In addition, as a rectangular wave is applied to the microcomputer 11 itself, current consumption in a Schmidt inverter 13 is also reduced to be suitably used for a battery driving equipment, etc., as the result.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microcomputer oscillator circuit suitable for reducing the current consumption of a microcomputer.

[0002]

2. Description of the Related Art A microcomputer operates in synchronization with a clock signal. An oscillation clock, which is the basis of this clock signal, is generated by free-running oscillation by the microcomputer itself, or it is rectangular from the outside of the microcomputer. It is necessary to apply a wavy oscillation clock.

Here, consider a case where the oscillation clock is generated by the former free-running oscillation. The oscillator circuit in this case is a crystal,
It is composed of an oscillator such as ceramics, a feedback resistor, a limiting resistor, a load capacitance, and an inverter circuit. Only this inverter circuit is built in the microcomputer, and other components are externally connected to the microcomputer. This is because the feedback resistance, the limiting resistance, the load capacitance, etc., are external components because they are indispensable for adjusting the state of the oscillation clock, and only the inverter circuit is an internal element. Since this inverter circuit is integrated in a microcomputer with a mask, the frequency of ceramics or the like is high (for example, 4 MHz).
z) The P-channel MOS transistor and the N-channel MOS transistor having a large size are used so that the oscillation vibrator can be sufficiently connected even when it is externally connected.

[0004]

However, since the inverter circuit built in the microcomputer converts the sine wave obtained from the oscillator into a rectangular wave, the slope portion near the amplitude center of the sine wave is an inverter circuit (P channel). Type and N-channel type MOS transistor common gate)
, The P-channel type and N-channel type MOS transistors connected in series are turned on at the same time, and the P-channel type MOS and N-channel type M transistors are turned on.
A through current will flow in the drain-source path of the OS transistor. As described above, since the size of both transistors is increased, the shoot-through current is also increased accordingly.

Incidentally, the oscillation frequency of the oscillator is 400 KHz under the condition that the power supply voltage of the microcomputer is 5 V and the inverter circuit is of a size that can support the oscillation frequency of up to about 6 MHz.
Then, as an example, a current of about 512 μA is consumed, and in the case of a general-purpose general-purpose microcomputer, this current consumption varies depending on the system scale, but is up to about half the current consumption of the entire microcomputer. turn into. Needless to say, the higher the oscillation frequency, the larger the current consumption.

To reduce the shoot-through current, the size of both the transistors forming the inverter circuit is reduced, or a resistor is connected to a power supply terminal, a ground terminal, etc. provided in the microcomputer, and the current of the inverter circuit is reduced. It is necessary to limit the current of the path. However, as in the former case, if the size of both transistors is made small, the versatility of the microcomputer is lacking and it is not possible to cope with a high oscillation frequency. Furthermore, since the gain of the inverter circuit is small, oscillation is sought to obtain the desired current consumption. Even if the frequency is changed, it is difficult to adjust the current consumption. Further, if a resistor is connected to the power supply terminal and the ground terminal of the microcomputer as in the latter case, the power supply input of the AD conversion circuit, the amplifier, etc. built in the microcomputer will change, and the microcomputer will operate normally. However, the above method is not a preferable means.

Therefore, the current consumption of the microcomputer is large, and this microcomputer has a problem that it is not suitable for a battery driven application set or the like. Therefore,
An object of the present invention is to provide an oscillator circuit of a microcomputer that can reduce current consumption and prolong battery life of battery-driven equipment.

[0008]

The present invention has been made to solve the above problems, and is characterized in that it has an external terminal to which a rectangular wave oscillation clock is applied from the outside. Then, a microcomputer that operates based on the oscillation clock is connected to the oscillation oscillator to convert an oscillation sine wave of the oscillation oscillator into a rectangular wave, and a limiting resistor is connected to the power supply line of the oscillation sine wave. An inverter circuit in which a wave-based through current is limited, and the microcomputer is operated by applying a rectangular wave output of the inverter circuit to an external terminal of the microcomputer.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be specifically described with reference to the drawings. FIG. 1 is a circuit block diagram showing an oscillator circuit of the microcomputer of the present invention. In FIG. 1, (1) is an inverter circuit, which is a P-channel type M
The drain and source paths of the OS transistor (2) and the N-channel type MOS transistor (3) are connected in series. The inverter circuit (1) forms a part of an oscillation circuit that forms an oscillation clock for the microcomputer. Reference numeral (4) is an oscillator such as crystal or ceramic, which is connected in parallel to the inverter circuit (1). (5)
Is a feedback resistor, which is a resistor that determines the bias of the oscillation point. (6) and (7) are load capacitors, which are connected between both ends of the oscillator (4) and the ground, and act as parameters that determine the stability of the oscillator circuit.
Reference numeral (8) is a limiting resistor, which is connected between the output of the inverter circuit (1) and one end of the feedback resistor (5) and the oscillator (4) to lower the gain in the high frequency range of the oscillation frequency, It suppresses abnormal oscillation of the frequency band. The limiting resistor (8) suppresses the oscillation amplitude and reduces unnecessary ringing in which the oscillation amplitude overshoots or undershoots the power supply or more. The oscillator circuit is configured by the above configuration.

Here, it is assumed that the inverter circuit (1) is configured to have a size capable of supporting an oscillation frequency of, for example, about 6 MHz at the maximum so as to support various oscillation frequencies of the oscillator (4). . However, as it is,
The through current of the inverter circuit (1) remains large.
Therefore, by utilizing the fact that the inverter circuit (1) is not built in the microcomputer, the inverter circuit (1)
A resistor can be inserted in the power supply path of the inverter circuit (1) in order to suppress the through current. Specifically, the power source V
Current limiting resistors (9) and (10) are respectively interposed between the DD and the source of the P-channel type MOS transistor (2) and between the ground VSS and the source of the N-channel type MOS transistor (3). To do. As a result, regardless of the operation of the microcomputer, the inverter circuit (1)
The through current can be limited.

Reference numeral (11) is the microcomputer described above, and the Schmitt inverter (13) is internally connected via the oscillation terminal (12). Oscillation terminal (12)
The output of the inverter circuit (1) is applied to. The output of the Schmitt inverter (13) serves as an oscillation clock, and the microcomputer (11) operates based on this oscillation clock. Schmidt inverter (13)
Is for removing a noise component included in the output of the inverter circuit (1). That is, a reliable oscillation clock without noise is applied to the microcomputer (11), and malfunction of the microcomputer (11) can be prevented. Further, since the rectangular-wave-shaped oscillation clock is applied to the oscillation terminal (12) of the microcomputer (11), M which constitutes the Schmitt inverter (13).
The through current does not flow through the OS transistor, and the current consumption of the microcomputer (11) itself can be reduced as compared with the conventional one.

Here, experimentally, an ammeter (14) was connected between the power supply VDD and one end of the current limiting resistor (9), the oscillation frequency of the oscillator (4) was 400 KHz, and the power supply VD was VD.
Current limit resistor (9)
When the values of (10) are both set to 3.9 KΩ, the ammeter (1
In 4), 244 μA could be measured. Therefore,
The current consumption of the microcomputer (11) can be reduced,
It can be applied to battery-powered equipment.

Further, if an oscillating inverter IC is used as the inverter circuit (1), a two-chip configuration with a microcomputer can be obtained, but the mounting area on the printed circuit board can be made as small as possible.

[0014]

According to the present invention, it is possible to provide an oscillator circuit for a microcomputer that consumes less current than before, and therefore, even when applied to battery-operated equipment, there is an advantage that the life of the battery can be extended.

[Brief description of drawings]

FIG. 1 is a circuit block diagram showing an oscillator circuit of a microcomputer of the present invention.

[Explanation of symbols]

 (1) Inverter circuit (4) Oscillator (9) (10) Current limiting resistor (11) Microcomputer (13) Schmidt inverter

Claims (2)

[Claims] 1. A microcomputer having an external terminal to which a rectangular wave oscillation clock is applied from the outside and operating based on the oscillation clock, and an oscillation oscillator connected to an oscillation sine wave of the oscillation oscillator. An inverter circuit for converting into a rectangular wave and limiting a through current based on the oscillating sine wave by connecting a limiting resistor to the power supply line, and outputting a rectangular wave output of the inverter circuit to an external terminal of the microcomputer. An oscillator circuit for a microcomputer, characterized in that the microcomputer is operated by applying the voltage to the microcomputer. 2. The microcomputer has a Schmitt inverter circuit, to which the rectangular wave output of the inverter circuit applied to the external input terminal is applied, and which performs an internal operation by the output, and a consumption current in the microcomputer. 2. The oscillator circuit for a microcomputer according to claim 1, wherein: