JPH0258806B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a voltage controlled oscillator whose oscillation frequency can be controlled by a voltage (current) applied to a control terminal.

Oscillators (voltage controlled oscillators) whose oscillation frequency can be controlled by a voltage applied to an input terminal (or a current flowing in) have been devised. FIG. 1 is a diagram showing an example of a conventional voltage controlled oscillator. This circuit is a complementary MOS for phase-locked loop (PLL).
It is used in integrated circuits and is composed of a semiconductor integrated circuit 101 and an external capacitor 102. 103 and 104 in the integrated circuit are level detection circuits that detect the voltage across the capacitor 102, and each time the voltage exceeds the threshold level of the level detection circuits 103 and 104, the capacitor 102 is connected in the opposite direction to reverse the charging direction. do. Capacitor 102
By changing the amount of current charged by the transistor 105 and resistors 106 and 107, the charging speed changes and the oscillation frequency can be changed.

In addition, as a conventional example, there is a method in which the capacitance of a capacitor constituting an oscillation circuit is changed using a variable capacitor or the like.

Before discussing the shortcomings of these conventional voltage controlled oscillators, an ideal voltage controlled oscillator is constructed from an integrated circuit.As shown in FIG. There is only an input terminal 203 and a power supply terminal for connection, and there is no need to provide any other terminal for connecting a capacitor or the like. Input terminal 203, output terminal 202
In most cases, the circuits connected to the oscillator can be constructed from semiconductor integrated circuits, so all oscillation circuits can be monolithically integrated. Furthermore, if elements such as capacitors that are directly related to the oscillation frequency of the oscillation circuit are placed outside the semiconductor integrated circuit, the stray capacitance of the connection pins will affect the oscillation, making it difficult to oscillate at a high frequency. In order to oscillate at a high frequency, the impedance of the element must be lowered, which increases power consumption.

As mentioned above, the drawbacks of conventional voltage controlled oscillators are summarized as follows: 1. Discrete components such as capacitors and variable capacitance diodes must be externally attached to the semiconductor integrated circuit.

2. Therefore, there is a disadvantage in that the space factor and the cost increase during assembly and manufacturing.

3. Difficult to oscillate at high frequencies due to stray capacitance.
If you try to force oscillation, power consumption will increase. The oscillation frequency also fluctuates as the charged body approaches the capacitor due to the influence of the surrounding environment.

The purpose of the present invention is to eliminate all of the drawbacks of the conventional voltage controlled oscillators mentioned above, and to present a new circuit for a voltage controlled oscillator that is stable and low power consumption by a completely monolithic integrated circuit, and to implement the voltage controlled oscillator in the configuration of an electronic device. The goal is to improve density, reduce costs, and improve performance.

Another object of the present invention is to convert a control voltage input to a current to control the oscillation frequency of a voltage controlled oscillator, to linearly change the oscillation frequency with respect to changes in the current, and to control the oscillation with high precision and high accuracy. The characteristic lies in what you do.

An example in which the present invention is implemented using a complementary MOS integrated circuit will be described below. Based on the same concept, it is also possible to implement integrated circuits based on other processes, such as bipolar integrated circuits.

FIG. 3 is a diagram for explaining the voltage controlled oscillator of the present invention. 301 to 30 _o constitute cells of the same shape. Each internal element will be explained using the cell 302 as an example. transistors 306 and 307
The gates are connected together and the drains are connected together to form an inverter circuit. Transistors 305 and 308 are transistors for controlling inflow and outflow currents, and control the inflow and outflow voltages of the inverter circuit by controlling gate voltages symmetrically from power supply potentials V _DD and V _SS , respectively. An odd number of inverter circuits whose inflow and outflow currents are controlled in this way are connected in series, and the output of the final stage is fed back to the input of the front stage. In this way, a ring oscillator is constructed. Transistors 309 and 310 are current control transistors 30
This is to symmetrically control the gate voltage of transistor 310, and by connecting P and N channel transistors with equal threshold voltage and current transfer rate as shown in the figure, the gate-source voltage of transistor 310 is set to V _C. For example, the gate-source voltage of transistor 309 becomes -V _C . By symmetrically changing the gate voltages of both the P and N channel transistors in this manner, the oscillation output waveform can be brought to approximately the center of the power supply. 3
Reference numeral 11 denotes a control terminal that controls the inflow and outflow currents of each inverter and the oscillation frequency using a control voltage V _C applied here. An amplifier 312 amplifies the oscillation output to a logic level. 313 is an output terminal.

FIG. 4 is a diagram showing another example for explaining the voltage controlled oscillator of the present invention, in which the inflow and outflow current control transistors 305 and 308 in FIG. 3 are replaced with the same transistors 401 and 402 in each stage. Compared to the circuit in Figure 3, the number of elements and current consumption can be reduced, but the oscillation waveform tends to be either positive or negative, and the circuit in Figure 3 is better for stable operation over a wide power supply voltage range. ing. still,
Symmetrically changing the gate voltages of the P and N channel current control transistors can be obtained as follows.

The threshold voltages of the transistors 309 and 310 are respectively V _TP and V _TN , and the coefficients proportional to the current transfer rate are 1/β _P and 1/β _N , respectively.
3 The current flowing through 10 is I, the source-drain voltage of transistor 309 is V _P , and if transistor 310 operates in the saturation region, then for 309, I = β _P /2 · (V _C - V _TP ) ² …(1) For 310, I=β _N /2・(V _P −V _TN ) ² …(2) From (1) and (2), β _P /2・(V _P −V _TP ) ² =β _N /2・(V _C −V _TN ) ^2Here , since V _TP = V _TN and β _P = β _N , V _P =
V _C and the gate voltage of the current control transistor changes symmetrically on the condition that the transistor 310 operates in the saturation region.

When the control voltage V _C and the oscillation frequency of the circuits shown in FIGS. 3 and 4 are plotted, the result is shown as 501 in FIG. 6. Here, the relationship between control voltage V _C and frequency changes non-linearly. This is because the symmetry of the gate voltage of the current control transistor is lost when the N-channel transistor 310 cannot be operated in the saturation region because the control voltage V _C is small. To correct this nonlinearity and make the relationship between the oscillation frequency and the control input linear, the inflow/outflow current control transistors 305, 308, or 40 in FIGS.
A circuit 309 that applies voltage to the gate of 1,402,
310 is changed as shown in FIG.

FIG. 5 is a diagram showing the most characteristic part of the voltage controlled oscillator of the present invention. 605 is a control voltage terminal, and the control voltage of this terminal is applied to the transistor 6.
06 converts it into a current and buffers and amplifies it, and resistor 6
09. In the figure, 607 is the gate of the transistor 305 in FIG. 3 and the gate of the transistor 401 in FIG. 4, and 608 is the gate of the transistor 308 and the gate of the transistor 40.
2 gates, respectively. transistor 60
4 and 610 both have their gates and drains connected and always operate in the saturation region. Here, the transistors 604, 610, and 612 have substantially the same threshold voltage and current transfer rate, which are transistor constants. Therefore, transistor 612 also operates in the saturation region, and the same current flows through transistor 610 or 612 as flows through transistor 604. That is, transistors 604, 610, 6
12 both operate in the saturation region as long as current flows,
Since the transistor constants are equal to each other,
607 and 608 can always output voltages that are symmetrical with respect to the power supply voltage. Therefore, when the relationship between the current ic flowing into the transistor 604 and the oscillation frequency is plotted, it is linearized as shown in FIG. 6 502.

As described above, by incorporating the present invention onto an integrated circuit, it is possible to create a voltage controlled oscillator capable of oscillating from several hundred Hz to the highest frequency to which the elements on the integrated circuit can respond. The additional capacitance of the oscillation circuit is the gate capacitance of the transistor on the integrated circuit, the wiring capacitance,
Parasitic capacitance such as PN junction capacitance (drain) can be reduced. This capacitance is one to two orders of magnitude smaller than when an external capacitor is added to the integrated circuit. Therefore, the circuit impedance can be increased accordingly, and the current during oscillation can be reduced.

Furthermore, the circuit for generating the gate voltage of the P, N channel current control transistor of the ring oscillator is replaced with a transistor 60 that converts the control voltage into a current.
6 and the transistor 6 whose gate and drain are connected
The series circuit of 04, the transistor 610 whose gate and drain are connected, and the gate of 604
A series circuit of a transistor 612 connected to the drain, and a series circuit of transistors 604 and 61
Since the threshold voltage of 0.612 and the current transfer rate are made equal, the three transistors always operate in the saturation region, the same current flows through each transistor, and a symmetrical gate voltage can always be generated at each drain. Therefore, the oscillation frequency of the ring oscillator is determined based on these current values, and as a result, the oscillation frequency of the ring oscillator has a linear relationship with these current values, resulting in high precision and high characteristics. It is possible to provide a voltage controlled oscillator.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a conventional voltage controlled oscillator. Second
The figure shows an ideal voltage controlled oscillator. Figure 3,
FIG. 4 is a diagram for explaining the voltage controlled oscillator of the present invention. FIG. 5 is a diagram showing a portion of the voltage controlled oscillator of the present invention. FIG. 6 is a diagram showing control voltage/current versus oscillation frequency characteristics regarding the voltage controlled oscillator of the present invention. 306, 307, 403, 404...Transistors forming the inverter, 305, 308, 4
01,402...Current control transistor that controls the inflow and outflow current of the inverter.

Claims (1)

[Claims] 1. A ring oscillator formed by cascading an odd number of inverters and feeding back the output of the last inverter to the input of the first inverter, and a first power line and the first power terminal of at least one of the inverters. a first current control transistor of a first polarity that is connected and controls a current flowing through the inverter according to a voltage applied to a control electrode;
a second current control transistor of a second polarity, which is connected between the power line of the inverter and the second power terminal of the at least one inverter, and controls the current flowing through the inverter according to the voltage applied to the control electrode; and a first power supply line having one end connected to the first power supply line.
a first series circuit formed by connecting in series a first control transistor with a polarity and a second control transistor with a second polarity, one end of which is connected to the second power supply line; a second series circuit formed by connecting in series a third control transistor connected to the power supply line and a fourth control transistor of a second polarity whose one end is connected to the second power supply line; The other end of the first control transistor is connected to each control electrode of the first control transistor and the first current control transistor, and the other end of the fourth control transistor is connected to the fourth control transistor. a transistor, the second control transistor and the second control transistor;
connected to each control electrode of the current control transistor of
The third control transistor determines a variable current flowing through the fourth control transistor based on the variable voltage applied to the control electrode, and the third control transistor determines a variable current flowing through the fourth control transistor based on the variable voltage applied to the control electrode. A first voltage that changes depending on the variable current is generated between the ends, and a first voltage that changes depending on the variable current is generated between the other end of the fourth control transistor and the second power supply line. A second current is generated, and the first and second
and the fourth control transistor, the threshold voltages and current transfer rates of the transistors are set to be approximately equal so that the currents flowing through each transistor are equal to each other, and the first voltage and the second voltage are equal to each other; The ring oscillator is a voltage controlled oscillator whose oscillation frequency changes according to the variable current.