JP3036756B2 - Oscillation circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillator circuit, and more particularly to an oscillator circuit using a comparator.

[Conventional technology]

FIG. 4 shows an example of an oscillation circuit to which a conventional comparator is applied. In the figure, the positive input terminal of the comparator COMP
In ⁺ has a resistor R between the power supply terminal V _CC and the ground terminal GND.
Connect ₁ and the R _2, and a resistor R ₃ is connected between the output terminal OUT. The negative input terminal In of the comparator COMP ^-
Is connected to one end of the capacitor C and the other end to the ground terminal GND. Furthermore, the negative input terminal terminal In ^- is connected to the output terminal OUT of the comparator via a resistor R ₄ from.

In this oscillation circuit, since the charge of the capacitor C is initially "0", the output terminal OUT of the comparator is at the high level "H" at this time, that is, almost at the power supply voltage V _CC . Therefore, the positive input terminal In ⁺ of the comparator COMP has:
A voltage obtained by dividing the power supply voltage is applied by the parallel connection value of the resistors R ₁ and R ₃ and the resistor R ₂ . When this divided voltage to a threshold V _H, Now, the output terminal OUT of the comparator COMP is “H”,
Capacitor C is gradually charged through the resistor R _4. The terminal voltage of the capacitor C exceeds the threshold value V _H when the comparator COMP
Is at a low level “L”, that is, almost at the GND level (0 V). Then, this time to the positive input terminal In ⁺ of the comparator COMP takes partial pressure of the parallel connection of the resistor R ₂ and R ₃ and the resistor R _1. If this divided voltage is a threshold _VL , Now, the output terminal OUT of the comparator COMP is because it is "L" capacitor C will discharge through the resistor R _4. When the terminal voltage of the capacitor C falls below the threshold value _VL , the output terminal OUT of the comparator becomes “H” again.

 The above is repeated, and the oscillation continues.

The waveform of each terminal is as shown in FIGS. 5 (a) and 5 (b). In Figure, T ₁ is the charging waveform by R ₄ of the capacitor C, the T ₁ is determined as follows.

T ₂ is the discharge waveform of the capacitor C due to R ₄ ,
The T ₂ is obtained in the following manner.

Next, when the oscillation frequency f is obtained, Becomes

[Problems to be solved by the invention]

In the above-described conventional oscillation circuit, since the threshold value is determined by the resistance, there is a problem that if the resistance value is small, the current flowing through the resistance increases power consumption.

In the above description, the output terminal of the comparator COMP is used.
OUT “H” level is the power supply voltage V _CC , “L” level is GN
It was assumed to be D potential. However, there is also a problem that the actual output terminal voltage of the comparator has a voltage drop error due to the saturation voltage inside the comparator, and the saturation voltage changes with temperature, so that the temperature characteristic of the oscillation frequency is poor.

Furthermore, the oscillation frequency is uniquely determined by the resistance R ₁ to R ₄ and capacitor C, there is a problem that can not be freely controlled by the parameter from the outside.

An object of the present invention is to provide an oscillation circuit that solves these problems.

[Means for Solving the Problems] An oscillation circuit according to the present invention includes a first transistor forming an inverting input of a differential amplifier, a second transistor forming a first non-inverting input, and a second An electronic switch connected to an output of the comparator, a capacitor connected between the inverting input and ground, and charging and discharging the capacitor. An oscillation circuit comprising: a charging / discharging unit; and a reference voltage source which is provided independently of a power supply of the comparator and which inputs a voltage divided by a resistor to each of the first and second non-inverting inputs. The output of the electronic switch is connected to the input of the
Connected to the non-inverting input, and controls the on / off operation of the electronic switch by the output of the comparator. While charging and discharging the capacitor, when the on / off of the electronic switch is in one state, the second forward input higher than the first forward input is set as an input threshold of a comparator, and the on / off of the electronic switch is turned on. An oscillation circuit wherein when the off state is the other state, the second forward input is stopped, and the first forward input is used as an input threshold of a comparator.

[Operation] In this configuration, the oscillation frequency can be accurately controlled by the reference voltage source, and the oscillation frequency can be stabilized. Also,
The frequency can be controlled by changing the reference voltage. In addition, the oscillation frequency can be determined by the ratio of the resistance that determines the threshold value, and lower power consumption can be achieved by increasing the resistance value.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

FIG. 1 is a circuit diagram showing one embodiment of the present invention. As shown, the first NPN transistor Q _1, the emitter and collector are respectively interconnected, and the first transistor Q ₁
And second and third NPN transistors Q ₂ and Q ₃ whose emitters are connected in common, and these constitute a differential amplifier. Further, PNP transistors Q ₄ and Q ₅ are connected as active loads of the differential amplifier, and an amplifier A for amplifying the voltage and current of a signal converted into a single end by the active load is connected.

The base of the transistor Q ₁ is an inverting input In ^- is configured as, the bases of the transistors Q _2, Q ₃ is the first and second forward input an In ₁ ^+, respectively, configured as an In ₂ ^+.

The transistors Q ₄ and Q ₅ have their emitters and their bases connected together, and their emitters are connected to a positive power supply V _CC . The collector of the transistor Q ₄ are commonly connected to the collector of the transistor Q ₂ and Q _3, is connected to the input of the amplifier A. The collector of the transistor Q ₅ is commonly connected to the collector of its own base and the transistor Q _1.

On the other hand, the between the common emitter connected to the ground potential of the transistor Q ₁ to Q ₃ is connected to a constant current source I ₀₁ to act as a bias of the differential amplifier. These constitute a comparator COMP.

The output of the amplifier A is connected to an NPN transistor Q ₆ as an electronic switch whose emitter is connected to the ground potential.
The base is connected. The transistor Q _6, in order to have a hysteresis width threshold value of the comparator COMP, to connect its collector to the base of the transistor Q _3.

Further, the collector of the transistor Q _6, and the emitter is commonly connected to connect the NPN transistors Q _7, Q ₈ constituting another differential amplifier. The other differential amplifier is connected to a current mirror circuit CM in which the collectors of the transistors Q ₇ and Q ₈ are connected to the input and output, respectively, and includes a constant current source I _{02 serving} as a reference for a capacitor charging / discharging current. It is connected between the commonly connected emitters of the transistors Q ₇ and Q ₈ and the ground potential. Note that a common terminal of the current mirror circuit CM is connected to the positive power supply V _CC . The base of the transistor Q ₈ is connected to the constant current source polarity switching threshold voltage V _T.
These components constitute a charging / discharging means for the capacitor C described later.

On the other hand, the transistor Q ₁ base, i.e. inverting input In
^- and to connect the capacitor C and the ground, to one end of the capacitor C, connects the collector of the current mirror circuit CM and the output of the transistor Q ₈ serving as an output of the capacitor charging and discharging means, respectively.

Further, the reference voltage _Vref is _divided to divide the transistors Q ₂ , Q
Voltage dividing resistors R ₁ for application to the base ₃ and the R _2, R ₃
R ₄ and the first forward input In ₁ ⁺ , the second forward input I
n ₂ ⁺ respectively.

In this configuration, the base potential of the transistor Q ₂ V _H
Then Becomes In addition, when the base potential of the transistor Q ₃ and V _L, Becomes Then, it is assumed that determine the resistance R ₁ to R ₄ such that V _H> V _L.

The first power-charge the capacitor C immediately after, "0" is output OUT of a is from comparator COMP at this time becomes "H", the transistor Q ₆ is turned off. Therefore, the threshold value of the comparator COMP becomes _VH because the higher one of the base voltages of the transistors Q ₂ and Q ₃ has priority. Then, because if you set the base potential V _T of the transistor Q ₈ such that V _T <V _H transistor Q ₈ is turned off, the constant current I ₀₂ charges the capacitor is folded by the current mirror circuit CM To go.

As a result of this charging, when the terminal voltage of the capacitor C exceeds the threshold value V _H , the output OUT of the comparator COMP becomes “L”,
Transistor Q ₆ is saturated turned on. At this time, the base potential V _H is substantially 0V, the transistor Q _2, the threshold of this time the comparator COMP becomes V _L. At this time, potential of the transistor Q ₇ is also a transistor Q ₇ is turned off since it is almost 0V, resulting, constant current I ₀₂ will discharge the capacitor C through the collector of transistor Q _8. And when the terminal voltage of the capacitor C falls below _VL ,
The output OUT of COMP becomes “H” again.

 Oscillation is continued by repeating the above.

Next, the oscillation frequency of the oscillator shown in FIG. 1 is obtained. 2 (a) to 2 (c) show terminal waveforms of FIG. If the charge mode time of the capacitor C is T ₁ and the discharge mode time is T ₂ , T ₁ = T ₂ = C / I ₀₂ (V _H −V _L ) (8) (8) Rewriting using equation (7), This oscillation frequency f is obtained from the equation (9). The oscillation frequency can be controlled by varying the reference voltage _Vref .

FIG. 3 shows an oscillation circuit according to a second embodiment of the present invention. This embodiment is obtained by replacing the constant current source charging and discharging of the capacitor C in the first embodiment to a single resistor R _5. The output terminal OUT of the resistor R ₅ has one end comparator COMP, the other end is connected to the capacitor C. Here, it is assumed that the output OUT of the comparator COMP can be performed in both directions of discharge and suction. When the output OUT of the comparator COMP is “L”,
The base of the NPN transistor Q ₉ shunting threshold V _H of about 0V is driven by the output obtained by inverting the comparator output OUT.
Other connections are the same as those in FIG. 1, and a description thereof will be omitted.

The input terminal waveforms of the comparator COMP in this embodiment are the same as those in FIG. 5 in the case of the conventional example. However, the input thresholds _VH and _VL of the comparator COMP for controlling the oscillation frequency can be controlled by an external reference voltage as in the case of FIG. Therefore, there is an advantage that application as a voltage controlled oscillator is possible. The oscillation frequency at this time is the same as that of equation (5). However, it may be a resistor R ₄ and the resistor R _5.

〔The invention's effect〕

As described above, the present invention has an effect that the oscillation frequency can be accurately controlled by the reference voltage source with a simple configuration, and the oscillation frequency has good stability. Further, since the frequency is controlled by the reference voltage source, the frequency can be easily controlled only by changing the voltage, and there is an effect that it can be used as a voltage controlled oscillator. Furthermore, since the oscillation frequency is determined by the ratio of the resistors that determine the threshold value, increasing the resistance value has the effect of reducing power consumption.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of a first embodiment of the present invention, FIGS. 2 (a) to 2 (c) are diagrams showing respective waveforms at the comparator input terminal of FIG. 1, and FIG. 3 is a second embodiment of the present invention. FIG. 4 is a circuit diagram of an oscillator circuit using a conventional comparator,
FIGS. 5 (a) and 5 (b) are diagrams showing waveforms at the comparator input terminal in FIG. 4, respectively. Q ₁ ~Q ₉ ...... transistor, R ₁ ~R ₅ ...... resistance, C ...... capacitor, A ...... amplifier, CM ...... current mirror circuit, I
_01, I ₀₂ ...... constant current ^{_{source, I n1 +, I n2 +}} , I n ...... non-inverting input terminal,
I _n ^- ...... inverting input terminal, GND ...... ground, COMP ...... comparator, OUT ...... output terminal, V _CC ...... supply terminal, V _ref ...... reference voltage, V _T ...... constant current source polarity switching threshold Voltage.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-59-62210 (JP, A) JP-A-57-20021 (JP, A) JP-A-60-10811 (JP, A) JP-A-59-210 19422 (JP, A) Actually open 1956-77143 (JP, U)

Claims (1)

(57) [Claims] A first transistor forming an inverting input of a differential amplifier, a second transistor forming a first non-inverting input, and a third transistor forming a second non-inverting input. An electronic switch connected to the output of the comparator, a capacitor connected between the inverting input and ground, charging / discharging means for charging / discharging the capacitor, and a power supply for the comparator. An oscillation circuit comprising: a reference voltage source that is provided independently and inputs a voltage divided by a resistor to each of the first and second non-inverting inputs; Connected to the input of the means and connected to the second non-inverting input, and controls the on / off operation of the electronic switch by the output of the comparator, and the charging / discharging means controls the on / off operation of the electronic switch. In response to the off operation, a constant current flows in or out to charge and discharge the capacitor, and when the electronic switch is on or off in one state, the second positive input is higher than the first normal input. The inverting input is used as the input threshold of the comparator, and when the electronic switch is in the on / off state, the second forward input is stopped and the first forward input is used as the input threshold of the comparator. Characteristic oscillation circuit.