JPS59178014A - Oscillation circuit - Google Patents

Abstract

PURPOSE:To decrease a resistance value of a resistor deciding an oscillating frequency by reducing a current of a reference current source by means of a current mirror circuit to use the current as a charge/discharge current of a capacitor of an oscillation circuit. CONSTITUTION:The oscillation circuit is constituted by CMOS inverters 1, 2, capacitors 5, 5' deciding the oscillation frequency, a differential amplifier circuit 10 as the reference current source, and the current mirror circuit 20. A divided voltage formed by resistors 16 and 17, i.e., a voltage at a point (a) is balanced at a voltage equal to a voltage at a point (b). A current which transistors 22 and 24 of the circuit 20 can flow is proportional to VDD/RS, where VDD is the power supply voltage and RS is a resistance value of a resistor 18.

Description

[Detailed description of the invention] Technical fields> The present invention relates to an oscillation circuit having a resistor and a capacitor.

<Prior Art> An example of a conventional oscillation circuit having a resistor and a capacitor is shown in FIG.

In the figure, 1, 2.3 are CMOS impulses, 4, 5, 5' are resistors and capacitors that determine the oscillation frequency,
These constitute an oscillation circuit.

6 is an output end. Further, capacitors 5 and 5' have equal capacitance values. A, B, shown in FIG. 1 of this oscillation circuit,
The voltage waveforms at each point C are shown in Figure 2 (a), (b), (
c). Here, VDD is a power supply voltage. That is, since the threshold voltage of a CMOS inverter is generally VDD/2, the capacitors 5 and 5' are at VDD/2.
/2'c is repeatedly charged and discharged from 0 to VDD, which causes oscillation. Therefore, the oscillation frequency f can be expressed as f=4RCAn2. However, R is the value of the resistor 4, and C is the capacitance of the capacitors 5 and 5'.

However, in such an oscillation circuit, resistance,
When integrated including capacitors, the following problems arise. The capacitor is MOS gate capacitance (3,5
4X10 pF/μ? 7'), but due to area constraints, a value of about 10 pF (corresponding to about 170 μm on the minus side) is a reasonable value. In this case, in order to obtain an oscillation frequency of, for example, about 400 KHz, the resistance value should be approximately 11 from the above formula.
becomes Ω to 0. The temperature coefficient of gate capacitance is small at 0.01 qb or less regardless of the capacitance value, but the temperature coefficient of resistance increases as the sheet resistance increases for both polysilicon resistance and diffused resistance, as shown in Figure 3, according to experimental results. The absolute value of increases. Therefore, as in the previous example, the resistance value is 1.
If the resistance is as large as 10Ω, the sheet resistance cannot be reduced considering the area required for integration, resulting in a large temperature coefficient. Therefore, there was a problem that the temperature characteristics of the oscillation circuit deteriorated.

<Object of the Invention> The present invention was made in view of the above-mentioned circumstances, and it is possible to reduce the sheet resistance by using a small resistance in an oscillation circuit having a resistor and a capacitor, even when integrated. The overall purpose is to provide an oscillation circuit with excellent temperature characteristics.

<Structure of the invention> Obtaining the current of the reference current source with a relatively small resistance value,
This current is reduced by a current mirror circuit to become a charging/discharging current for the capacitor, and the charging/discharging of the capacitor is switched depending on the output state of the positive feedback circuit.

<Example> Hereinafter, an example of the present invention will be described in detail based on the drawings. Incidentally, the same parts as in the prior art are designated by the same reference numerals and the explanation thereof will be omitted.

In FIG. 4 showing one embodiment of the present invention, reference numeral 10 denotes a differential amplifier circuit as a reference current source, which includes two P-channel transistors 11.12, two N-channel transistors 13.14, and the P-channel transistors 13.14. Transistor 11.
A resistor 15 connected between each of the 12 sources and the power supply 40
It consists of Then, a divided voltage of the power supply voltage is generated by a resistor 16.degree. 17, and the divided voltage point ai is connected to the gate of a P-channel transistor 11 which is an input of the differential amplification circuit 10. Further, the gate of the P channel transistor 12, which is another input of the differential amplifier circuit 10, is connected to the resistor 18 and the N
Connected to the drain of channel transistor 19.

Furthermore, the output of the differential amplifier circuit 10, ie, the drain of the P-channel transistor 11, is connected to the gate of the N-channel transistor 19.

Reference numeral 20 denotes a current mirror circuit, which is composed of two P-channel transistors 21 and 22 and two N-channel transistors 23 and 24.

The gates of the N-channel transistors 23 and 24 are connected to the drains of the P-channel transistors 11, which serve as output terminals of the differential amplifier circuit 10. Further, the output of the current mirror circuit 20, that is, the drains of the P-channel transistor 22 and the N-channel transistor 24 are C
It is connected to each source of a P-channel transistor 25 and an N-channel transistor 26 that constitute a MOS inverter.

The output of the CMOS inverter is CMOS inverter 1
The output of the CMOS inverter 1 is input to the icMOS inverter 2. Capacitors 5 and 5' of equal capacitance are connected between the input of CMOS inverter 1 and the output of CMOS inverter 2, and between the input of CMOS inverter 1 and ground (GND).

Next, the effect will be explained.

When the gate voltage of the P-channel transistor 12, that is, the voltage at the point b, becomes lower than the divided voltage created by the resistors 16 and 17, that is, the voltage at the point a, the P-channel transistor 12 further operates in the direction of turning on. Therefore, its drain voltage increases, and at the same time, the gate voltage of N-channel transistor 13 increases. Since the drain current of this N-channel transistor 13 is kept almost constant by the P-channel transistor 11, an increase in the gate voltage causes the drain current of the N-channel transistor 13 to
The voltage between the drain and source of is suddenly lowered. Then, since the gate voltage of the N-channel transistor 19 becomes low, the drain voltage of the N-channel transistor 19 is increased, thereby preventing the voltage at point b from decreasing.

Similarly, when the voltage at point b becomes higher than the voltage at point a, the opposite is true as described above, so the voltage at point b is balanced at a voltage equal to the voltage at point a.

Now, assuming that the divided voltage k VDD/2 (VDD is the power supply voltage) and the value of the resistor 18 are '1zRs, the drain current of the N-channel transistor 19 is VDD/2 Rs.
It will be.

Further, if the ratio of W/L of the N-channel transistor 19 (W indicates the channel width and L indicates the channel length) and the W/L of the N-channel transistor 24 of the current mirror circuit 20 is N:1, then the N-channel transistor The drain current that can flow through 24 is VDD/2NR
It becomes 8.

Furthermore, the W/L of the N-channel transistor 19 and the N-channel transistor 23 of the current mirror circuit 20
'i to the same level, W/ of P channel transistor 21
If the ratio of L and W/L of the P-channel transistor 22 is 'iN:1, then the P-channel transistor 22
Similarly, the drain current that can flow is VD D/2
It becomes N Rs. However, the W/L of the P-channel transistor 21 is set to a value that allows a sufficient current to flow (VDD/2NRs t7).

Therefore, the circuit of FIG. 4 can be replaced with an equivalent circuit as shown in FIG. In the figure, 31 and 32 indicate current sources. That is, the oscillation circuit of this embodiment can be said to have the resistor 4 removed by 9 compared to the conventional one, and the sink output current and source output current of the CMOS inverter 3 to be VDD/2NR8.

The oscillation frequency of this circuit is expressed by f=-NRsC from the waveform of FIG. However, C is the capacitance of the capacitors 5 and 5'. For this reason, in conventional circuits, for example, 400 KH
In order to obtain the oscillation frequency of z, a resistor of about 110Ω is required, but in the circuit of this embodiment, the resistance value can be reduced by setting N. For example, N=100, C=10pF
, f=400KHz, Rs=6250.

Therefore, it is possible to reduce the area of polysilicon resistors, diffused resistors, etc., and also to reduce the sheet resistance and the absolute value of the temperature coefficient, so even when such an oscillation circuit is integrated, it is possible to obtain one with excellent temperature characteristics. Obtainable.

Next, FIG. 7 shows another embodiment.

The present embodiment is composed of a reference current source 10', a resistor 18, and an N-channel MO3 transistor 19', and the other configurations are the same as in the first embodiment.

In such a circuit, if the channel width/channel length (Stshi'L) of the N-channel MO8) transistor 19' is set to a sufficiently large value, the current flowing through the resistor 18 will increase the power supply voltage to vDDXN-channel MO3) transistor 19'.
If the value of the threshold voltage k vTHz resistor 18 is R8, it becomes approximately equal to (VDD - VTH)/Rs. Here, if VDD>VTR, the current flowing through the resistor 18 can be approximated to kVDD/Rs.

Therefore, considering the same as the first embodiment, the oscillation frequency f is expressed as f=-NRsC, so the resistance value can be reduced by setting N as in the first embodiment, resulting in excellent temperature characteristics. An oscillation circuit can be obtained. Furthermore, according to this embodiment,
Since the threshold voltage of the transistor is not canceled by the differential amplification circuit as in the first embodiment, the threshold voltage is slightly affected by temperature fluctuations, but the circuit configuration of the reference current source can be greatly simplified, and the circuit elements can be The reduction in number has a significant cost effect.

Although this embodiment has been described using a unipolar process, it goes without saying that it can also be realized using a bipolar process.

<Effects of the Invention> As explained above, according to the present invention, the current of the reference current source obtained by a relatively small resistance value is reduced by the current mirror circuit 7 to become the charging/discharging current of the capacitor of the boosting circuit. Therefore, the value of the resistance that determines the oscillation frequency can be reduced, and the sheet resistance can be reduced to realize an oscillation circuit with excellent temperature characteristics in an all-semiconductor integrated circuit.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a conventional example, Fig. 2 is a voltage waveform diagram of each part shown in Fig. 1, Fig. 3 is a temperature I+ = temperature diagram of a diffused resistor and a polysilicon resistor, and Fig. 4 is a diagram of the present invention. 5 is an equivalent circuit diagram of FIG. 4, FIG. 6 is a voltage waveform diagram of each part of FIG. It is. 1. 2.3...CMOS i/verter 5,5'・
...Capacitor 10, 10'...Reference current source 18...Resistor 20...Current mirror circuit 31.32...Current source 40...Power supply patent applicant Nissan Motor Co., Ltd.

Claims (1)

[Claims] A reference current source, a current mirror circuit that uses the output of the reference current source as an input current, a charging/discharging circuit that charges and discharges a capacitor with the output current of the current mirror circuit, and a charging/discharging circuit that charges and discharges a capacitor according to the output state. An oscillation circuit characterized by comprising a positive feedback circuit that switches discharge.