JPS61113303A - Semiconductor integrated circuit - Google Patents

Abstract

PURPOSE:To vary easily the oscillating frequency in response to the operating state of a microcomputer by selecting a capacitor being contributing to the time constant of a CR oscillator comprising a C-MOS. CONSTITUTION:The CR oscillator consists of inverters 1,1, a resistor R and a capacitor C. The capacitor C, however, comprises plural capacitors C5-CN connected in parallel, whose connection depends on transfer gates 5-N. That is, the transfer gates 5-N are switched by a control signal of a control circuit 10, and when a gate is turned on, a capacitor corresponding to the gate is connected selectively. Thus, a signal 10a from the microcomputer is inputted to the control circuit 10, the connection of the capacitors C5-CN is decided properly and then the oscillating frequency is decided. Thus, the oscillating frequency is varied easily depending on the operating state of the microcom puter.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a semiconductor integrated circuit which uses a CMOS transistor as an active element, is formed on the same half-circuit substrate including a capacitor, and generates a clock for a microcomputer. Regarding.

[Takumi rice technology]

Conventionally, a CR oscillator like the one shown in Figure @2 has been conveniently used as the system clock of a microcomputer.As for the transistor used in the inverter 1.2, a CM OS l-transistor transistor was used because of its low power consumption. This CR oscillation k & is an astable multivibrator whose oscillation frequency and number f are v v - v f = 1 / [: C, R (An V,."th"
"2V..-v,h)'3. Here, vcc is the voltage, and Vth is the logic threshold voltage of the inverter.

■When th=1/2Vcc, VC is 172.2CR in f becomes.

Incidentally, the oscillation frequency of the CR oscillator of a conventional microcomputer was uniquely fixed as C and R being constant values. This excavation period 111jtdi is determined according to the fastest processing speed of microcomputers), and microcomputers are not necessarily always 1CN.
6CMO is not working hard to make city management a necessity.
When the operating frequency of the 8 transistor increases, the power consumption increases and the advantage of low power consumption disappears. Therefore, if the microcomputer's processing speed is not the highest, @vc reduces the oscillation frequency mantissa of the C8 oscillator. If it were possible to do so, it would be extremely advantageous in terms of power consumption.

[Problem that the invention seeks to solve]

The purpose of the present invention is to reduce the oscillation frequency by adjusting the oscillation frequency by considering the above-mentioned circumstances,
A variable CR transmitter? The purpose is to provide it as a semiconductor integrated circuit.

Means for solving the CtOJ problem] This semiconductor integrated circuit uses a 0MO8 transistor as an active element and is a CR@oscillator constructed on the same substrate.
Finally, a plurality of fixed rectangular capacitors that determine the oscillation frequency, a transfer gate that electrically connects each two of the capacitors, a control circuit that controls the transfer cost, and all installations/7. The required processing speed of the microcomputer is VC@-.
Programmably operate the control circuit (by turning each transfer gate on and off, you can find the frequency?
change. This allows the power consumption of the oscillation circuit to be minimized.

〔Example〕

Figure 1 shows a circuit block diagram of an embodiment of the present invention.

The configuration of the C8 oscillator is the same as the conventional example, with inverters 1 and 2
are connected in series, and a capacitor C1 is connected between both ends thereof, and a resistor R is connected between both ends of the inverter 1. However, the capacitance C is the same as the one shown in the figure, consisting of multiple capacitances C5 to CM1.
Each volume tcs~CW is a transfer gate 5~
The connection is activated by N. In other words, transfers 5 to N are turned on and off by a control signal from the control circuit 10, and when they are on, their corresponding capacitors are connected.

In the above circuit, a signal 10a is input from the microcomputer (not shown) to the control circuit 10, and the capacitors 05 to CN are connected as appropriate. The generated capacitance C is ＠Maru〇 [Overall effect] As detailed above, depending on the processing speed of the microcomputer, CR＠frequency of the oscillator? Since the clock frequency can be changed even during processing that does not require high processing speed, the generator that generates the clock frequency is fixed and continues to generate the highest frequency, causing unnecessary consumption of power. Never happened. Therefore, for microcomputer systems that must reduce power consumption as much as possible, is this the most suitable @oscillator? can get 0

[Brief explanation of drawings]

FIG. 1 is a circuit block diagram of an embodiment of the present invention, and FIG. 2 is a circuit block diagram of a conventional example. 1, 2..., inverter, 5~N...transfer, 10...control circuit C, C5~CN...each head, R...tooth. Day 1 Figure 2

Claims (1)

[Claims] A CR oscillator using a CMOS transistor as an active element and configured on the same substrate includes a plurality of fixed capacitors that determine an oscillation frequency, a transfer gate that electrically connects each of the capacitors, and a control that controls the transfer gate. A semiconductor integrated circuit characterized by being provided with a circuit.