JPH04334114A - Triangle wave oscillating circuit - Google Patents

Abstract

PURPOSE:To revise an oscillating frequency and a triangle waveform without replacing a timing resistor and a timing capacitor. CONSTITUTION:A charging current source section outputting a charge current to a timing capacitor CT is provided with plural current source sections 6-8 and charging current source control switched 22-24 selecting individually the validity/invalidity of an output of each of the current source sections 6-8. A discharging current source section outputting a discharging current to the capacitor CT has plural current source sections (transistor(TRs) 12-14) and is provided with discharging current source control switches 25-27 selecting individually the validity/invalidity of an output of each of the current source sections 12-14. A symmetrical triangle wave is obtained by selecting a charging current and a discharging current to/from the capacitor CT equal to each other and an asymmetrical triangle wave is obtained by selecting a charging current and a discharging current to/from the capacitor CT so as to be different from each other. Moreover, the frequency of a triangle wave is changed by changing only the current without changing a charge/discharge current ratio.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a triangular wave oscillation circuit, and more particularly to a triangular wave oscillation circuit that charges and discharges a timing capacitor using a constant current source.

0002

[Prior Art] As shown in FIG. 3, a conventional triangular wave oscillation circuit uses a reference voltage Vr at a terminal 2 and a timing resistor RT.
A reference current source (IR
EF) 28, current sources 29 and 30 that create the charging current I1 and discharging current I2 of the timing capacitor CT by a current mirror circuit, and a triangular wave output signal (VO
) 16 has reached the set highest potential VH (terminal 17) of the triangular wave, a comparator (COMP) 15;
A comparator (COMP) 18 and a comparator 15 detect that the set minimum potential VL (terminal 19) has been reached.
, a reset set latch circuit (R-S latch) 20 that controls a charging/discharging changeover switch 21 based on the output of the comparator 18.

Next, the operation of the conventional circuit will be explained. Reference current I0 is determined by reference voltage Vr and timing resistor RT.

[Formula 1] I0=Vr/RT. The charging current I1 and the discharging current I2 are generated by a current mirror circuit, and are generated by a timing capacitor CT.
The charging/discharging current will be . The output of the comparator 15 becomes Lo when the output voltage VO becomes higher than the set highest potential VH.
When the level W becomes low, it becomes a High level, and the output voltage of the comparator 18 is set to the lowest potential VL.
When it becomes lower, it becomes a Low level, and when it becomes higher, it becomes a High level. Therefore, the output of the R-S latch circuit 20 is
As shown in FIG. 4, when the output voltage VO rises, VL
Low level below → VH, High above VH
h level. When the output voltage VO falls, VH
Above → High level up to VL, Low level below VL
level. The charging/discharging switch 21 is R-S.
The output of the latch circuit 20 is discharged at High level, and the output is at Low level.
It moves to charge at W level. Therefore, if the output voltage VO in the initial state is less than or equal to VL, the charging mode is entered because VO < VL, and the timing capacitor CT is charged...■ The timing capacitor CT is charged, and the output voltage VO
increases......■ When VO > VH, the discharge mode starts...
…■The timing capacitor CT is discharged and the output voltage VO decreases…■When VO < VL, the charging mode is activated…
……■ From then on, repeat the above steps ■ to ■ to oscillate a triangular wave. still,
In this case, the oscillation frequency f is expressed as follows.

0004

[Mathematical 2] i...Charging/discharging current
(A)C...Capacity of timing capacitor CT (F)VH...Highest potential of triangular wave
(V)VL...Minimum potential of triangular wave (V)

[Problems to be Solved by the Invention] However, since the conventional triangular wave oscillation circuit described above is composed of one current source for charging and one for discharging, only one type of triangular waveform is generated. Therefore, it was not possible to change the rise and fall time ratio.

Another disadvantage is that the oscillation frequency can only be changed by replacing the timing resistor and capacitor.

The present invention has been made in view of the above-mentioned conventional circumstances, and therefore, an object of the present invention is to provide a novel triangular wave oscillation circuit that makes it possible to eliminate the above-mentioned drawbacks inherent in the conventional technology. It's about doing.

[0007]

[Means for Solving the Problems] In order to achieve the above object, in a triangular wave oscillation circuit according to the present invention, a charging current source section that outputs a charging current to a capacitor has a plurality of current source sections. The discharge current source section that outputs the discharge current to the capacitor has a plurality of current source sections, and each of these It is configured to include a discharge current source control switch that individually switches between enabling and disabling the output of the current source section.

[0008]

[Operation] A symmetrical triangular wave can be obtained by selecting the charging current and the discharging current to the capacitor equally by each current source control switch, and an asymmetrical triangular wave can be obtained by selecting them differently.

Furthermore, by changing only the amount of current without changing the charge/discharge current ratio, the frequency of the triangular wave can be changed.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments of the present invention will be specifically explained with reference to the drawings.

FIG. 1 is a circuit configuration diagram showing a first embodiment of the present invention, and is an example constructed using CMOS transistors.

Referring to FIG. 1, reference number 2 indicates an operational amplifier, and the reference voltage Vr applied to the non-inverting input terminal 1 of the operational amplifier 2, the timing resistor RT, and the Nch The transistor 4 constitutes a reference current source.

Here, the reference current IREF is expressed by the following equation (3).

[0014]

[Math. 3] IREF = Vr /RT Vr: Reference voltage, RT: Timing resistor No.
．． 0Pch transistor 5 and No. 1Pch transistor 6 and No. 1Pch transistor 6. 2Pch transistor 7 and No. n
The Pch transistor 8 and the Pch transistor 9 constitute a current mirror. Pch transistor 5~
By making the sizes of transistors 9 the same, the same amount of current =IREF flows between the source and drain of each transistor. Further, the Pch transistors 6 to 8 serve as current sources for charging the timing capacitor CT.

[0015]No. 0Nch transistor 11 and No.
．． 1Nch transistor 12 and No. 1Nch transistor 12. 2Nch transistor 13 and No. The mNch transistor 14 constitutes a current mirror circuit.

By making the length of the Nch transistors 12 to 14 twice that of the Nch transistor 11, the current flowing through the Nch transistors 12 to 14 is reduced to
Twice the amount of channel transistor 11 = 2×IREF flows. Further, the Nch transistors 12 to 14 serve as a current source for discharging the timing capacitor CT.

The high level side voltage detection comparator 15 has a triangular wave output signal (VO) 16.
It outputs a high level when the output signal VO is lower than the highest set voltage VH of the triangular wave applied to the non-inverting input terminal 17, and outputs a low level when the output signal VO is higher than the highest set voltage VH.

The low level side voltage detection comparator 18 has a triangular wave output signal (VO) 16.
It outputs a high level when the output signal VO is higher than the minimum setting voltage VL of the triangular wave applied to the inverting input terminal 19 of the circuit, and outputs a low level when the output signal VO is lower than the minimum setting voltage VL.

The reset set latch circuit 20 resets (R) the output of the high level side voltage detection comparator 15.
The output of the low level side voltage detection comparator 18 is the input of the set (S).

The logic is: R=H, S=H, Q, -Q: maintain previous state R=H,
S=L, Q=L, -Q=H R=L, S=H, Q=H, -Q=L R=L, S=L, Q=L, -Q=L Here, R : Reset input, S: Set input, Q: Output,
-Q: Inverted output H: High level, L: Low level.

Therefore, this reset set latch circuit 2
0 is a triangular wave output signal (VO) 16 is VO < VL
When , the output Q becomes a low level and the voltage of the output signal VO rises.When VL<VO<VH, the output Q remains at a low level, and when VO>VH, the output Q becomes a high level. Here, the voltage of the output signal VO drops,
When VL<VO<VH, the output Q remains at a high level, and when VO<VL, the output Q changes to a low level.

[0022] Therefore, the charge/discharge changeover switch 21 is
The output of the latch circuit 20 is “OFF” (disconnected) at a low level.
state, and the output of the latch circuit 20 becomes “ON” at a high level.
(conducting) state.

Reference numerals 22 to 24 indicate control switches for the charging current sources 6 to 8, and by turning these switches ON or OFF, the charging current sources 6 to 8 are enabled or disabled.

Reference numerals 25 to 27 are control switches for the discharge current sources 12 to 14, and these switches are turned on and off.
``By doing so, the discharge current sources 12 to 14 are enabled or disabled.

Charging current sources 6-8 and discharging current sources 12-
If the same number of 14 are valid, a symmetrical triangular wave will be obtained. For example, if three of each are enabled, charging current = IREF × 3 discharging current = IREF × 3 - (2 × IREF ) ×
3=-3×IREF, the charging and discharging current values become equal, and the triangular wave becomes symmetrical.

Furthermore, by changing the number of effective current sources, the charging/discharging current changes in proportion to the number. In other words, the oscillation frequency can be changed without changing the timing resistor RT and the timing capacitor CT.

Next, the waveform of the triangular wave can be changed by using different numbers of current sources for charging and discharging. For example, in order to set the time ratio of the rise and fall of the triangular wave to 1:2, it is sufficient to enable two current sources for charging and enable one current source for falling.

In other words, if rise time: fall time = a: b, b charging current sources and a discharging current sources should be enabled (a and b are natural numbers). ).

FIG. 2 is a circuit diagram showing a second embodiment of the present invention.

Referring to FIG. 2, 1 times (×1) Pch
The transistor 31 is No. 0 Pch transistor 5
The current of this transistor 31 is IREF.

The double (×2) Pch transistor 32 is No. This is the size of the Pch transistor 5 of 0, but only the length is doubled, and the current of this transistor 32 is 2×IREF.

The n-times (×n) Pch transistor 33 is No. This is the size of the Pch transistor 5 of 0, but only the length is multiplied by n, and the current of this transistor 33 is n×IREF.

[0033] Double (2×) Nch transistor 34,
4x (4x) Nch transistor 35, 2mx (2m
The Nch transistor 36 of No. The size of the Nch transistor 11 of 0 is changed only in length, and a current proportional to the changed amount flows through each transistor.

For example, rise time:fall time=2:1 can be achieved by selecting and validating a charging power source and a discharging current source such that charging current x 2=discharging current.

[0035]

As explained above, according to the present invention, since the amount of current charging and discharging the timing capacitor can be changed by turning the switch "ON" and "OFF", the timing resistor and the timing capacitor The oscillation frequency can be changed without replacing the oscillation frequency.

Further, according to the present invention, the waveform of the triangular wave can be changed by varying the amount of current for charging and discharging.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing a first embodiment according to the present invention.

FIG. 2 is a circuit configuration diagram showing a second embodiment according to the present invention.

FIG. 3 is a circuit diagram showing a conventional example.

FIG. 4 is a waveform diagram of a triangular wave output signal and an R-S latch output.

[Explanation of symbols]

RT...Timing resistor CT...Timing capacitor 1...Non-inverting input terminal of operational amplifier 2...Operation amplifier 4...Nch transistor 5...No. 0Pch transistor 6...No. 1Pch transistor 7...No. 2Pch transistor 8...No. nPch transistor 9...Pch transistor 11...No. 0Nch transistor 12...No. 1Nch transistor 13...No. 2Nch transistor 14...No. mNch transistor 15... Comparator for high level side voltage detection 16... Output signal of triangular wave (VO) 17... Input terminal for highest set voltage VH of triangular wave 18... Comparator for low level side voltage detection 19... Input of lowest set voltage VL of triangular wave Terminal 20...Reset set (R-S
) Latch circuit 21...Charging/discharging switch 22-24...Charging current source control switch 25-27...
Discharging current source control switch 28...Reference current source 29...Charging current source 30...Discharging current source 31...1x Pch transistor 32...2x Pch transistor 33...nx Pch transistor 34...2x Nch transistor 35...4 times Nch transistor 36...2×m times Nch transistor

Claims (1)

[Claims] 1. A reference current source that outputs a current serving as a reference for a charging/discharging current to a capacitor, a charging current source section that outputs a charging current to the capacitor, and a discharging current source that outputs a discharging current from the capacitor. a voltage detection section that detects a triangular wave voltage; a reset set latch section that outputs a charge/discharge switching signal for the capacitor using the output of the voltage detection section; In the triangular wave oscillation circuit equipped with a charge/discharge switch that switches between charging and discharging, the charging current source section has a plurality of current source sections, and the output of each current source section is individually switched between enable and disable. The discharge current source section has a plurality of current source sections, and the discharge current source section includes a discharge current source control switch that individually switches between enabling and disabling the output of each current source section. Triangular wave oscillation circuit.