JPH09121142A - Oscillation circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stabilize a charging/discharging operation to be stable independently of the fluctuation of a power source voltage by providing a current supply source which is functioned as a constant current source for temp. change and is propotionated to the fluctuation of the power source voltage for the fluctuation of supply voltage and controlling charging/discharging current. SOLUTION: The output of an operational amplifier 201 is transmitted to the gate of NTr 202 and the source terminal output of NTr 202 becomes a negative feedback voltage to the reverse input terminal of the operational amplifier 201. Current I0 permitted to flow in PTr is expressed an expression (number 10) and I0 changes only by relying on the power source voltage VDD regardless of the change of an element characteristic by the temp. change of NTr 202. Then, in a current switch part 103, the charging/discharging current IC1 and IC2 rely on charging/discharging control current which is decided by the output voltage of a current source part 101. Therefore, since the current source part 101 is functioned as the constant current source as against temp. change, a normally stable oscillation frequency is obtained without depending on the change of the element characteristic owing to temp. change.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillation circuit capable of stabilizing frequency characteristics in a CMOS semiconductor device using the charge / discharge characteristics of capacitors.

[0002]

2. Description of the Related Art Conventionally, as an oscillation circuit for generating a sequential control clock inside a CMOS semiconductor device, a CR oscillation circuit utilizing a charge / discharge characteristic of a capacitor and a resistor has been used.

FIG. 4 shows a block diagram of a conventional oscillator circuit. A conventional oscillator circuit has a reference potential generation unit 401 connected to a power supply voltage VDD, a reference output voltage of the reference potential generation unit 401, and an output potential (VC) of a charge / discharge circuit including a capacitor 404 and a discharge resistor 405. And an ON resistance switch section 403 which uses the digital output signal of the comparator section as a control signal. The oscillation output signal is the digital output signal output from the comparator unit 402.

FIG. 5 shows a circuit example of the oscillator circuit of FIG. The reference potential generator 401 is composed of resistors R1, R2, and R3, and is connected by a resistor R1, R2, and R3 connected in series between a power source (hereinafter referred to as VDD) and a ground (hereinafter referred to as GND). This is a resistance voltage dividing circuit that generates potentials VH and VL. The comparator unit 402 includes two comparators (CM
P1, CMP2) and an RS flip-flop 501. The CMP1 has the inverting input of the reference potential VH and the non-inverting input of the output potential (VC) of the capacitor 404 and the discharge resistor 405, and the output is input to the set terminal of the RS flip-flop 501. CMP2 is the reference voltage VL
Is a non-inverting input, and the output voltage (VC) of the capacitor 404 and the discharge resistor 405 is an inverting input, and the output is input to the reset terminal of the RS flip-flop. The on-resistance switch unit 404 is a P-channel MOS transistor (hereinafter PT
r) 502, and the comparator unit 40
The output of the RS flip-flop 2 is input to the gate terminal of the PTr 502, the drain terminal is connected to VDD, and the source terminal is connected to the charging / discharging circuit including the capacitor 404 and the discharging resistor 405.

The operation of the conventional oscillator circuit will be described below with reference to FIG. Immediately after the power source VDD is turned on, the capacitor C has no electric charge, so the voltage VC is at the GND level. As a result, CMP1 compares VC (0V) and VH and outputs the L level, and CMP2 compares VL and VC (0V) and outputs the H level. The RS flip-flop 501 outputs an L level, which is input to the gate terminal of the PTr 502 and turns the PTr 502 ON. When the PTr502 is turned on, the current IC1 flows between the drain and the source of the PTr502, and the charging of the capacitor 404 starts. The capacitance of the capacitor 404 is C, the charging current IC1 and the output potential VC of the charge / discharge circuit are

[0006]

(Equation 1) , And rises with time t.

When VC rises and VC <VL, CM
P2 outputs L level. VC further rises, VC
When> VL, CMP1 outputs the H level. As a result, the RS flip-flop 501 outputs the H level,
This is input to the gate terminal of PTr502, and PTr5
Turn 02 off. When the PTr502 is turned off, the charge accumulated in the capacitor 405 is discharged by the discharge resistor 40.
A current I C2 flows through the capacitor 5 and discharge of the capacitor 404 starts. The output potential VC of the discharge circuit is

[0008]

(Equation 2) It is represented by and falls over time.

When VC drops and VC> VL, CMP
1 outputs an L level. VC drops further and VC <
When it becomes VL, COMP2 outputs H level. As a result, the RS flip-flop 501 outputs the L level,
This is input to the gate terminal of PTr502, and PTr5
Turn 02 on. When the PTr502 is turned on, the current IC1 flows between the drain and the source of the PTr502, and the charging of the capacitor 404 starts again. The oscillation output signal Xo can be obtained by repeating the above operation.

The output potential VC of the charge / discharge circuit at this time,
The relationship between the time t and the oscillation output signal Xo is shown in FIG. When the charging time of the capacitor 404 is Δt1 and the discharging time is Δt2, the oscillation period tOSC is

[0011]

(Equation 3) Can be expressed as Here, when the capacitance of the capacitor 404 is C, the resistance value of the discharge resistor 405 is R, and the on-resistance of the PTr 502 is RONPch,

[0012]

(Equation 4)

[0013]

(Equation 5) Since C and R are constant, the oscillation cycle tOSC is PTr.
It depends on the on-resistance RONPch of 502. Since the PTr502 is a CMOS transistor, the threshold voltage Vth and the on-resistance RONPch change depending on the temperature change. Further, the reference potentials VH and VL, which are the reference for comparison in the comparator section, are

[0014]

(Equation 6)

[0015]

(Equation 7) Therefore, VH and VL change depending on the change of the power supply voltage. Furthermore, due to fluctuations in the power supply voltage VDD, the capacitor 4
04 charging current IC1 also changes, but IC1 is PTr502
It does not change in proportion to VDD because it is determined by the characteristics of. Therefore, when the power supply voltage VDD fluctuates, VC obtained from the equation 1 and VH and VL obtained from the equations 2 and 3 respectively fluctuate, and the operation of the comparator section becomes unstable.

[0016]

As described above, since the conventional oscillation circuit depends on the element characteristics of the on-resistance switch section and the fluctuation of the power supply voltage, it is difficult to obtain a stable output signal with little fluctuation. there were.

[0017]

In order to solve the above problems, in the oscillator circuit of the present invention, the charge and discharge characteristics of the capacitor are utilized to charge and discharge the capacitor in the oscillator circuit which generates a desired oscillation output signal. The discharge current is generated by the current source unit and supplied to the charging / discharging capacitor via the current switch unit. The current source unit maintains a constant output current with respect to a temperature change, maintains an output current proportional to the power supply voltage with respect to a change in the power supply voltage, and the current switch unit causes the capacitor to respond to the oscillation output signal. It has a function of switching between sending a charging current and extracting a discharging current, and the current value changes only in proportion to the output current output from the current source section, regardless of changes in element characteristics due to temperature changes. .

The reference potential that determines the frequency of the output oscillation signal fluctuates in proportion to the fluctuation of the power supply voltage, and the charging / discharging potential of the charging / discharging capacitor changes in proportion to the change of the charging / discharging current. The charging / discharging current fluctuates in proportion to the fluctuation of the power supply voltage. Both the reference potential and the charge / discharge potential fluctuate in proportion to the fluctuation of the power supply voltage.

Since the rising and falling timings of the output oscillation signal are determined by the result of comparison between the reference potential and the charging / discharging potential, fluctuations in both power supply voltages cancel each other out and a constant timing is maintained. , The frequency of the output oscillation signal does not depend on the fluctuation of the power supply voltage,
It can always maintain a constant value.

[0020]

DETAILED DESCRIPTION OF THE INVENTION The oscillation circuit of the present invention will be described below with reference to the drawings. A block diagram of the oscillator circuit of the present invention is shown in FIG. The oscillator circuit of the present invention is connected to a power supply voltage VDD and is connected to a current source unit 101 for generating a charging / discharging control current, and a power supply voltage VDD and a charging / discharging capacitor 102. The current switch unit 103 that switches the output charge / discharge control current, the reference potential generation unit 104 that is connected between the power supply voltage VDD and the GND, and that generates the reference potential, the charge / discharge potential VC of the charge / discharge capacitor and the It is composed of a comparator unit 105 that compares with a reference potential generated by the reference potential generation unit 104. The oscillation output signal is the digital output signal output from the comparator unit 105.

A circuit example of the oscillator circuit of FIG. 1 is shown in FIG. The configuration of the current source unit 101 is as follows. The operational amplifier 201 has a potential obtained by dividing the power supply voltage VDD by resistors R1 and R2 as a non-inverting input, and an output potential as a gate input N.
Channel MOS transistor (hereinafter referred to as NTr) 20
Negative feedback is applied with the drain potential of 2 as the inverting input. On the other hand, a P-channel MOS transistor (hereinafter referred to as PTr) 20 having a drain terminal connected to the power supply voltage VDD
3 and 204 have a common gate terminal,
Of the PTr 203 and the source terminal of the PTr 203. The source terminal of the NTr 202 is connected to the GND via the resistor R3. The source terminal of PTr204 is connected to the current switch unit.

The structure of the current switch section 103 is as follows. The PTr 205 and PTr 206 have a common drain terminal and are connected to the source terminal of the PTr 204. The oscillation output signal is input to the gate terminal of the PTr 206 via an inverter, and the inverter output is further input to the gate terminal of the PTr 205 via the inverter. The gate terminals of the NTr 207 and the NTr 208 are common, and the source terminal of the PTr 205 and the NTr 208 are the same.
It is connected to the drain terminal of 207. NTr20
7 and the source terminals of NTr 208 are connected to GND. The drain terminal of the NTr 208 is connected to the source terminal of the PTr 206 and the charging / discharging capacitor 102,
The potential at this point is called charge / discharge potential VC.

In the reference potential generator 104, resistors R4, R5 and R6 are connected in series between VDD and GND as in the conventional example. The comparator unit 105 includes two comparators (209, 210) and two NORs (211, 21).
2) An RS flip-flop composed of CM
P209 is an inverted input of the reference potential VH, and the charge / discharge potential V
With C as the non-inverting input, the output is connected to the first input terminal of NOR211. The CMP 210 has the non-inverting input of the reference voltage VL and the inverting input of the charging / discharging potential VC, and the output is connected to the first input terminal of the NOR 212. NOR2
The output terminal of 12 is connected to the second input terminal of the NOR 211, and the output terminal of the NOR 211 is connected to the second input terminal of the NOR 212. The output of NOR211 becomes the oscillation output signal X0.

The operation of the oscillator circuit of the present invention will be described below with reference to FIG. First, the operation of the current source unit 101 will be described in detail. The potential V divided by VDD by R1 and R2
1 is

[0025]

(Equation 8) And is input to the non-inverting input terminal as the reference potential of the output of the operational amplifier 201. The output of the operational amplifier 201 is transmitted to the gate of the NTr 202, and the output of the source terminal of the NTr 202 becomes a negative feedback voltage to the inverting input terminal of the operational amplifier 201. On the other hand, the current flowing through the PTr 203 is I
If 0,

[0026]

(Equation 9)

[0027]

(Equation 10) Holds. As a result, I0 changes only depending on the power supply voltage VDD regardless of the change in the element characteristics due to the temperature change of the NTr 202. Since the PTr204 shares a gate terminal with the PTr203 and constitutes a so-called current mirror, the current I0 flowing through the PTr204 becomes equal to the current I flowing through the PTr203. From the above, the current source unit 10
Reference numeral 1 functions as a constant current source with respect to temperature changes, and as a current source that supplies a current proportional to changes in VDD with respect to changes in the power supply voltage VDD. Current I flowing through PTr204
Is transmitted to the current switch unit 103 as a charge / discharge control current.

Next, the current switch section 103 will be described in detail. When the oscillation output signal X0 is L, the PTr206 is ON, the PTr205 is OFF, and the charge / discharge control current I is P
It becomes the charging current IC1 for charging the capacitor 102 via the Tr 206. When the oscillation output signal X0 is H, PTr2
05 is turned on, PTr206 is turned off, and the charge / discharge control current I flows into GND via PTr205 and NTr207. At this time, the discharge current IC2 of the capacitor 102 flows through the NTr 208.
And the gate terminal are commonly used to form a so-called current mirror, the current IC2 flowing through the NTr 208 is NTr2.
It becomes equal to the current I flowing through 07. From the above,

[0029]

[Equation 11] Is established. From this, the capacitor 102
The charging / discharging current (IC1, IC2) depends on only the current I0 supplied from the current source, regardless of the device characteristics of the transistor.

The reference potential generator is a circuit for generating the reference potentials VH and VL by resistance-dividing the power supply voltage VDD by the resistors R3, R4 and R5, as in the conventional circuit example.
Than,

[0031]

(Equation 12)

[0032]

(Equation 13) Therefore, VH and VL change in proportion to the power supply voltage VDD.

Finally, the operation of the comparator section will be described in detail. Immediately after the power source VDD is turned on, the capacitor C has no electric charge, so the voltage VC is at the GND level. As a result, the CMP 209 compares VC (0V) with VH and outputs the L level, and the CMP 210 outputs VL and VC (0V).
And are compared with each other to output the H level. NOR211 outputs H level. This is through the inverter, PTr2
05 is turned off and PTr206 is turned on. PTr
When 206 is turned on, the current I C1 flows and the charging of the capacitor 102 starts, as described in the description of the current switch unit. When the capacitance of the capacitor 102 is C, the output potential VC of the charging / discharging circuit is represented by the equation 1, and rises with time t.

When VC rises and VC <VL, CM
P210 outputs the L level. VC further rises,
When VC> VL, the CMP 209 outputs the H level. As a result, the NOR211 outputs the L level. This turns on PTr205 via an inverter,
Turn off Tr206. When the PTr 205 is turned on, the discharge of the capacitor 102 starts, as described in the description of the current switch section. Output potential of discharge circuit VC
Is expressed by Equation 2 and drops with time.

When VC drops and VC> VL, CMP
209 outputs an L level. VC drops further, V
When C <VL, COMP 210 outputs H level. As a result, the NOR211 outputs the H level, and this turns off the PTr205 via the inverter,
Turn on Tr206. When the PTr2062 is turned on, the charging of the capacitor 102 starts again. The oscillation output signal Xo can be obtained by repeating the above operation.

The output potential VC of the charge / discharge circuit at this time,
The relationship between the time t and the oscillation output signal Xo is shown in FIG. If the charging time of the capacitor 102 is Δt1 and the discharging time is Δt2,

[0037]

[Equation 14]

[0038]

(Equation 15) Since the oscillation output frequency tOSC can be expressed by Equation 3, from Equation 11,

[0039]

(Equation 16) Can be expressed as Here, VH and VL change in proportion to changes in the power supply voltage VDD, and I also changes in proportion to changes in the power supply voltage VDD.
The oscillation output frequency tOSC can always maintain a constant value.

Further, the charge / discharge currents IC1 and IC2 of the capacitors are
Depends on the charging / discharging control current determined by the output voltage of the current source unit 101, and as described above, the current source unit 101 functions as a constant current source with respect to temperature changes. It is possible to always obtain a stable oscillation frequency without being affected by changes in element characteristics such as changes in resistance value.

By using the oscillating circuit of the present invention in the 1 MHz oscillating circuit, the frequency fluctuation rate of about 10% in the conventional circuit can be reduced to about 1%.

In this embodiment, PTr203 and PT
The dimension ratio of r204, NTr207, and NTr208 was set to 1: 1. However, changing this value to adjust the amount of current does not depart from the gist of the present invention.

[0043]

As described above, by using the oscillation circuit of the present invention, it is possible to obtain a stable output signal that does not depend on the element characteristics of the transistor and the fluctuation of the power supply voltage. This also enabled high frequency oscillation.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of an oscillator circuit of the present invention.

FIG. 2 is a circuit diagram showing an example of the oscillator circuit shown in FIG.

FIG. 3 is a diagram showing a relationship between a charge / discharge current VC of the oscillation circuit shown in FIG. 2 and an oscillation output signal XO.

FIG. 4 is a circuit configuration diagram of a conventional oscillator circuit.

5 is a circuit diagram showing an example of the oscillator circuit shown in FIG.

6 is a diagram showing a relationship between a charge / discharge current VC of the oscillation circuit shown in FIG. 5 and an oscillation output signal XO.

[Explanation of reference numerals] 102 charge / discharge capacitor 404 charge / discharge capacitor 405 discharge resistance

Claims (3)

[Claims] 1. An oscillation circuit for generating a desired oscillation output signal by utilizing the charge / discharge characteristics of a capacitor, which is connected to a power supply voltage, maintains a constant output current with respect to temperature changes, and has a stable power supply voltage. On the other hand, it is connected to a current source part that maintains an output current proportional to the power supply voltage, a power supply voltage and a charging / discharging capacitor, and the output current of the current source part is charged / discharged during charging by the oscillation output signal. The charging current of the capacitor, when discharging, a current having the same value as the output current of the current source unit is the discharging current of the charging / discharging capacitor, a current switch unit, connected to the current switch unit, the current switch unit The charge and discharge is performed by the output current, the charge and discharge capacitor that outputs the charge and discharge potential, and the resistance divided by the resistor connected in series between the power supply voltage and the ground potential, the first reference potential,
It is connected to a reference potential generation unit that generates a second reference potential lower than the first reference potential, the charge / discharge capacitor and the reference potential generation unit, and is connected to the first reference potential and the second reference potential. Each of the reference potential and the charge and discharge potential of the charge and discharge capacitor is compared,
An oscillator circuit, comprising: a comparator unit that outputs an oscillation output signal whose rising edge and falling edge are determined according to a comparison result. 2. A change in the charge / discharge potential due to a change in the power supply voltage of the charging / discharging capacitor and a change in the reference potential due to a change in the power supply voltage of the reference voltage generated by the reference potential generation unit have a proportional relationship. The oscillator circuit according to claim 1, wherein: 3. The current switch unit switches between sending a charging current to the charging / discharging capacitor and drawing a discharging current from the charging / discharging capacitor according to the oscillation output signal, and the current value thereof is an element due to a temperature change. 2. The oscillator circuit according to claim 1, wherein the oscillator circuit changes only in proportion to an output current output from the current source section, regardless of fluctuations in characteristics.