JP2003067076A - Semiconductor integrated circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable time measurement (Wake-up operation) with low current consumption while using an RC oscillator capable of ultrasonic welding. SOLUTION: A constant-current source 10 is connected to an external capacitor 12 via an external connection terminal 11 of a microcomputer. The connection point between the constant-current source 10 and capacitor 12 is connected to the uninverted input terminal (+) of a comparator 13. The reference voltage VB of a reference voltage source 14 is connected to the inverted input terminal (-) of the comparator 13. The connection point between the constant-current source 10 and capacitor 12 is connected to an N-channel MOS transistor 15 for discharging. When the microcomputer is in standby mode, the RC oscillation circuit is stopped and the time measurement is performed according to the decision signal from the comparator 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor integrated circuit having a time measuring function.

[0002]

2. Description of the Related Art In a conventional microcomputer, a so-called wake-up operation is performed to measure a standby time. As the oscillation signal source for this time measurement, it is general to use a crystal oscillator whose current consumption is as small as about 5 μA.

That is, during standby, the operation of the microcomputer is stopped and only the crystal oscillator and the frequency divider for dividing the oscillation signal from the crystal oscillator are operated. Then, in accordance with the output of the frequency divider, the microcomputer is woken up (restarted) after a predetermined time has elapsed, and the time during which the microcomputer is in the standby state is calculated by the CPU processing. As a result, the low current consumption of the microcomputer and the highly accurate time measurement were realized at the same time.

[0004]

By the way, in order to externally attach the crystal oscillator to the microcomputer, it is necessary to solder it onto a printed circuit board on which the microcomputer is mounted. However, the crystal oscillator has a problem that ultrasonic welding cannot be performed. This ultrasonic welding includes the step of melting the solder by ultrasonic waves, and therefore the characteristics of the crystal oscillator may deteriorate.

On the other hand, when an RC oscillator capable of ultrasonic welding is used, it consumes a large current of about 100 μA and cannot be used for the wakeup operation of a microcomputer.

Therefore, there has been a demand for a system which enables a wakeup operation of a microcomputer while using an RC oscillator capable of ultrasonic welding.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and in a semiconductor integrated circuit having an RC oscillator for creating an operation clock, a constant current source and , A capacitor charged by the constant current source, a reference voltage source for generating a reference voltage, a terminal voltage of the capacitor and the reference voltage are compared, and a determination signal is output when the terminal voltage reaches the reference voltage. A comparator,
A discharge transistor for discharging the electric charge of the capacitor according to a standby signal, and stopping the operation of the RC oscillator according to the standby signal,
It is characterized in that time measurement is performed according to the determination signal output from the comparator.

According to this structure, since the capacitor is charged by the current of the constant current source, the terminal voltage of the capacitor can be measured for a predetermined time by determining the level using the comparator. At this time, the current of the constant current source is suppressed to, for example, about 1 μA, and the RC oscillator is stopped to realize low current consumption. That is, it becomes possible to measure time (wake-up operation) with low current consumption while using an RC oscillator capable of ultrasonic welding.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Next, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a time measuring circuit incorporated in the semiconductor integrated circuit of the present invention. 2 shows an RC oscillator circuit built in the semiconductor integrated circuit of the present invention. In the following, the semiconductor integrated circuit is assumed to be a microcomputer as an example.

In FIG. 1, the constant current source 10 is connected to an external capacitor 12 via an external connection terminal 11 of the microcomputer. The connection point between the constant current source 10 and the capacitor 12 is connected to the non-inverting input terminal (+) of the comparator 13. Also, the inverting input terminal (-) of the comparator 13
Is applied with the reference voltage VB of the reference voltage source 14.
The connection point between the constant current source 10 and the capacitor 12 is connected to the N-channel MOS transistor 15 for discharging.

In FIG. 2, a NAND circuit 20 has one input terminal to which the external connection terminal 21 of the microcomputer is connected, and the other input terminal to which the standby signal * STBY is input. The output of the NAND circuit 20 is connected to the external connection terminal 22 of the microcomputer via the even-numbered stages of inverters. A resistor 2 having a resistance value R is provided between the external connection terminal 21 and the external connection terminal 22.
3 is connected, and a capacitor 24 having a resistance value C2 is connected to the external connection terminal 21.

During standby, the standby signal * STBY becomes low level and oscillation stops. During the operation of the microcomputer, the standby signal * STBY becomes high level, the oscillation operation is performed with the time constant determined by the resistance value R and the capacitance value C2, and the operation clock is created based on the oscillation signal. The microcomputer executes the program operation based on this operation clock.

Also, an external resistor 23 and a capacitor 2
4 can be soldered on a printed circuit board on which a microcomputer is mounted by ultrasonic welding.

Next, the operation sequence of the microcomputer having the above configuration will be described. When the microcomputer enters the standby state, R
The operation of the C oscillator circuit stops. (Standby signal * STBY
Becomes low level), and at the same time, the gate signal DC of the N-channel MOS transistor 15 for discharging is discharged.
HG becomes high level, the N-channel type MOS transistor 15 is turned on, and the charge of the capacitor C1 is removed. Then, the N-channel MOS transistor 15 is turned off. Only the constant current source 10 is operating in the standby state. The capacitor 12 is charged by the current (for example, 1 μA) from the constant current source 10, and its terminal voltage (= voltage of the non-inverting input terminal (+) of the comparator 13) rises. When the terminal voltage of the capacitor reaches the reference voltage VB, the comparator 13 outputs a determination signal (high level). This determination signal is called a wakeup signal, and the standby state of the microcomputer is released based on this signal. Then, the RC oscillator circuit starts operating again, and the microcomputer starts operating based on the operation clock generated from the oscillation signal from the RC oscillator circuit.

Then, the value of the register (the initial value is assumed to be reset to zero) in the microcomputer is incremented. After that, it enters the standby state again and the gate signal DCHG
Is set to a high level, the discharge N-channel type MOS transistor 15 is turned on, and the capacitor 12
Remove the electric charge. By repeating the above steps, the value of the register when the final exit from the standby state is read out to count the time during which the standby state is entered.

Next, a second embodiment of the present invention will be described with reference to the drawings. FIG. 3 shows a time measuring circuit according to the second embodiment of the present invention. In the first embodiment, the determination signal (wakeup signal) from the comparator 13
Based on, the microcomputer was restarted and the time was measured by software.

In this embodiment, the output of the comparator 13 further detects the determination signal output by the comparison 13 and outputs a detection pulse, and a counter circuit 18 (for example, a counter circuit 18 for counting the number of detection pulses). TFF) is provided, and a function of measuring time by hardware is added.
The detection circuit 19 includes a delay circuit 16 including an odd number of stages of inverters to which a determination signal is applied, and an output of the delay circuit 16 and an AND circuit 17 to which the determination signal is applied.

As described above, in the standby state,
When the terminal voltage of the capacitor 12 rises and reaches the reference voltage VB, the output of the comparator 13 rises to a high level.
The detection circuit 19 detects the determination signal of the comparator 13 and creates a detection pulse. The counter circuit 18 counts the number of detection pulses.

Next, the operation sequence of the microcomputer of the second embodiment described above will be described. When the microcomputer enters the standby state, R
The operation of the C oscillator circuit (FIG. 2) stops. At the same time (the standby signal * STBY becomes low level), at the same time, the gate signal DCHG of the N channel type MOS transistor 15 for discharging becomes high level, the N channel type MOS transistor 15 is turned on, and the charge of the capacitor C2 is removed. Then, the N-channel MOS transistor 15 is turned off. Only the constant current source 10 is operating in the standby state. The capacitor 12 is charged by the current (for example, 1 μA) from the constant current source 10, and its terminal voltage (= voltage of the non-inverting input terminal (+) of the comparator 13) rises. When the terminal voltage of the capacitor 12 reaches the reference voltage VB, the comparator 13 outputs a determination signal (high level).
This determination signal is called a wakeup signal, and the output of the comparator 13 rises to a high level. The detection circuit 19 detects the determination signal of the comparator 13 and creates a detection pulse. The counter circuit 18 counts the number of detection pulses. By repeating the above steps, the value of the counter at the time of finally exiting the standby state is read to count the time in the standby state.

As described above, according to the present embodiment, since all the time measurement is performed by hardware, it is not necessary to operate the RC oscillating circuit on the way unlike the first embodiment. It can be converted to electricity.

[0021]

According to the present invention, R which enables ultrasonic welding
While using the C oscillator, time measurement (wakeup operation) can be performed with low current consumption. In particular, it is effective in building a battery management system for the low end.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a time measuring circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of an RC oscillator circuit according to the first embodiment of the present invention.

FIG. 3 is a circuit diagram of a time measuring circuit according to a second embodiment of the present invention.

[Explanation of symbols]

10 constant current source 11 External connection terminal 12 capacitors 13 Comparator 14 Reference voltage source 15 N-channel MOS transistor 16 delay circuit 17 AND circuit 18 counter circuit 19 Detection circuit 20 NAND circuit 21,22 External connection terminal 23 Resistance 24 capacitors

Claims (3)

[Claims] 1. A semiconductor integrated circuit having an RC oscillator for generating an operation clock, comprising: a constant current source, a capacitor charged by the constant current source, a reference voltage source for generating a reference voltage, and the capacitor. And a discharge transistor for discharging the electric charge of the capacitor in response to a standby signal, and a comparator for outputting a determination signal when the terminal voltage reaches the reference voltage. A semiconductor integrated circuit characterized in that the operation of the RC oscillator is stopped in response to a signal, and the time is measured in response to a determination signal output from the comparator. 2. A detection circuit that detects a determination signal output from the comparator and outputs a detection pulse, and a counter circuit that counts the number of detection pulses. The semiconductor integrated circuit described. 3. The detection circuit includes a delay circuit including an odd number of stages of inverters to which the determination signal is applied, and an output of the delay circuit and a gate circuit to which the determination signal is applied. Item 2. The semiconductor integrated circuit according to item 2.