JP2788732B2 - Oscillation circuit - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a circuit for automatically controlling the gain of a tank type voltage controlled oscillator.

2. Description of the Related Art A voltage-controlled oscillator is a simple oscillator whose frequency is proportional to an externally applied voltage. Integrated circuit VCO
Is typically just an RC multivibrator in which the charging current of the capacitor can be changed in response to a control input. However, the duration of the switching transient at higher frequencies will be a large percentage of the oscillation period and will cause a drift of the center frequency. The duration of the switching transient is related to the parasitic capacitance of the circuit, the resistance of the circuit, the transconductance of the transistor and the input resistance of the transistor, all of which are affected by temperature. Voltage controlled oscillator circuits that are more resistant to temperature use a tank circuit composed of inductors and parallel capacitors. However, as a circuit like this,
No circuit is known that adequately controls the swing between the peaks of the tank nodes of the circuit.

SUMMARY OF THE INVENTION Accordingly, an improved tank-shaped voltage controlled oscillator is provided.

The present invention provides a voltage controlled oscillator circuit having a tank circuit that generates vibration. This circuit is coupled to ground from the biased end of the tank,
The biased end includes a diode assembly that sets a constant voltage bias point with respect to ground. A current sink circuit coupled to the oscillating end of the tank draws current from the tank for half a cycle and controls the gain of the tank. An AGC discharge circuit coupled to the AGC capacitor is connected to the resistor chain for setting a reference voltage substantially independent of the parameters of the active device, and the reference voltage and the AGC capacitor, and the tank voltage is related to the reference voltage. And a discharge transistor that acts to discharge the AGC capacitor when the value exceeds

While the novel features believed unique to the invention are set forth in the following claims, the invention itself and other features and advantages will be best understood from the following detailed description of the drawings.

Embodiment FIG. 1 shows a voltage controlled oscillator having a coil 10 and a voltage variable capacitor 14. Another capacitor 12 couples the bias line 11 to ground. Logic clamp input line
28 is coupled to the base of Schottky transistor 18 via Schottky diode 26. Resistor 30 biases transistor 18 on. Resistor 24 acts to help turn off transistor 18 by passing the charge on the base to ground. Transistor 16 couples the emitter of transistor 18 to ground and adds one emitter-base voltage to the input logic threshold on line 28. Transistor 20, coupled to the collector of transistor 18, is diode-connected, similar to transistor 16, and adds an emitter-base voltage between the base of Schottky transistor 22 and the collector of transistor 18. Resistor 32 provides a bias current for the base of transistor 22 and a collector current for transistor 18.

The emitter of Schottky transistor 22 is coupled to ground via diode-connected transistors 50, 52, 54, thus setting the bias voltage on line 11 to three emitter-base voltages above ground. The collector of transistor 22 drives load resistor 34 and is also coupled via Schottky diode 42 to the base of NPN transistor 44. A pair of diode-connected transistors 36, 38 couple the collector of transistor 22 to its emitter. The collector of transistor 44 is connected to high-voltage line 58
And its emitter is connected to the coil 10 via the clamp resistor 56. The emitter of transistor 48 is coupled to the emitter of transistor 44, and its collector is connected to the base of transistor 44. The base of transistor 48 is coupled to line 11 via resistor 46. Transistor
The collector of the transistor 60 of the current steering circuit composed of a differential pair composed of 60 and 62 is coupled to the alternating voltage end of the coil 10 and the base of the transistor 62. The base of transistor 60 is connected to line 11 and transistors 60 and 62
Is connected to ground via the collector of NPN transistor 78. The alternating voltage side end of coil 10 is coupled to line 82. This line is connected to the collector of transistor 60, the base of transistor 62, and the base of transistor 96. Transistors 66 and 74 form a current mirror,
The size of transistor 66 is five times the size of transistor 74. Therefore, a current five times as large as a predetermined current flowing through the transistor 74 passes through the transistor 66. The dimensional ratio of transistor 66 to transistor 74 may be other values.

The base drive for transistors 66 and 74 is provided by the emitter of transistor 70. Transistor 70
Is connected to the collector of transistor 74. The voltage drop between the collector and the emitter of the diode-connected transistor 76, the voltage drop across the resistor 72 and the transistor
74 base-emitter junction voltage (this is transistor 66
Of the transistor 70 determines the emitter-base voltage of the transistor 70, and thus the current therethrough. Thus, resistor 72 determines the current through transistor 74, and the dimensional ratio of transistors 66, 74 determines the current through transistor 66.

The value of resistors 63 and 64 and the emitter-base voltage of transistor 68 determine the voltage at the emitter of transistors (68; and 88). The voltage at the emitter of transistor 68 on line 73 is equal to:

V ₇₃ = V ₁₁ − (1 + R ₆₃ / R ₆₄ ) V _be where V _be is the emitter-base voltage of the transistor 68. The pair of PNP transistors 76, 92 also form a current mirror, and the current through transistor 92 is equal to the current through transistor 76 because of the same size, but other dimensional ratios may be used. Both emitters of transistors 76 and 92 are connected to positive voltage supply line 58.
Connected to. The collector of transistor 92 is connected to an AGC node 90, which also has an AGC capacitor 100 coupled thereto. A current mirror consisting of transistors 76 and 92 now has a node 90, mainly as determined by resistor 72.
About 200 microamps is always applied to the AGC capacitor 100 coupled to. The collector of transistor 88 is AG
Connected to C node 90, the emitter of which is connected to emitter line 73. The current through resistor 98 determines the emitter-base voltage of transistor 96. Transistor 96 applies to the base of transistor 88 a voltage equal to the voltage on line 82 minus the emitter-base voltage of transistor 96. The current in transistor 88 flows only when the base voltage exceeds the voltage defined on line 73 well. When transistor 88 conducts its collector current, it removes charge from capacitor 100, thus reducing the voltage on line 90.

The emitters of the differential NPN transistors 60 and 62 are transistors
Connected to 78 collectors. The collector of transistor 62 is connected to Vcc line 58 and the collector of transistor 80. The collector of transistor 60 is connected to tank line 82. The emitter of transistor 80 is connected to one end of resistor 84 and the other end is coupled to diode-connected transistor 86. As the voltage across the tank oscillates, transistor 62 turns on for the positive half cycle and turns off for the negative half cycle. Transistor 60 conducts current from tank line 82 to keep the current through transistor 78 constant as determined by the voltage at node 90 and the resistance of resistor 84. The tank gain is determined by the collector current through transistor 60.

As the voltage on tank line 82 changes due to tank oscillations, emitter follower transistor 96 changes the current through resistor 98. The changing voltage across the resistor 98 is
Applied to the base of transistor 88. Transistor 88
Starts discharging current from the AGC node 90 when its base voltage reaches the voltage on line 72 plus the forward emitter-base voltage drop. The voltage at which transistor 88 begins to discharge AGC node 90 is determined by the voltage on line 73. This voltage is mainly controlled in the sense that the higher the voltage of the emitter line 73, the larger the amplitude of the peak voltage across the AGC capacitor 100. The secondary control factor is the ratio of the collector current of transistor 66 to the collector current of transistor 92, whereby the lower the ratio, the greater the peak amplitude. As the oscillator amplitude increases, transistor 88 causes the increasing total current per cycle (integrated discharge current) to reach a steady state where the integrated discharge current balances the current sourced from the collector of transistor 92. By discharging, negative feedback is provided in the AGC circuit for stabilizing the amplitude of the oscillator.

Since transistor 80 only draws a small base current from AGC node 90, the discharge of AGC capacitor 100 is determined primarily by resistors 63 and 64. The voltage on the AGC capacitor 100 determines the voltage at the emitter of transistor 80, and thus across resistor 84. This is because the drop across transistor 86 is just the forward drop of the diode. The current through transistor 78 is related only to the dimensional ratio of this transistor to transistor 86, and is thus a constant multiple of the current through resistor 84. As the AGC voltage increases, more current is drawn from the emitters of the differential pair 60,62, thereby increasing the current drawn from the tank and reducing its gain. Transistor 88 turns on and extracts charge from AGC capacitor 100
Since the C threshold level is primarily related to the resistance ratio and the emitter-base voltage, there is relatively little dependence on temperature sensitive factors such as transistor gain.

The operation of the tank circuit clamp is designed to stop the oscillation within two cycles of the input logic for activating the clamp line 28 and, when unclamped, start from a known state and free-run. When the logic clamp signal on line 28 is low, transistor 18 is biased off and transistor 22 is on. Therefore, diode-connected transistors 36 and 38 are kept off by the low collector-emitter saturation voltage of transistor 22. Due to the low voltage at the collector of transistor 22, transistor 44 remains off, and thus the coil, in series with capacitor 12,
High impedance remains in parallel with the tank circuit composed of 10 and the capacitor 14. Therefore, the tank circuit vibrates freely.

When the voltage on line 28 rises above the sum of the emitter-base voltages of transistors 16 and 18 minus the forward drop across diode 26, transistor 18 turns on, lowering the base voltage of transistor 22 and lowering it. Turn off. Diode connected transistors 36 and 38 are resistors 3
Combined with 4, this determines the voltage at the collector of transistor 22. Thus, transistor 44 turns on, driving current through resistor 56 and coil 10. resistance
Reference numeral 56 is outside the semiconductor bar provided with the clamp circuit and other related circuits, and is set so that the inductor current is the same in the clamped state and the unclamped state. When the inductor current is determined in this way, when the inductor current is cut off,
The oscillation is resumed from the peak position in the oscillation corresponding to the peak amplitude of the inductor current.

When used in a phase locked loop, the voltage variable capacitor 14
The voltage across is typically governed by the input signal provided by the integrator / charge pump (not shown). When this voltage increases, the capacitance of the voltage variable capacitor 14 decreases, and the oscillation frequency increases.

The effect of transistor 48 is to turn on if the emitter of transistor 44 is accidentally grounded, thus turning off transistor 44.

Although the invention has been described with reference to an embodiment, it should not be construed as limiting the invention. From the above description, those skilled in the art will readily perceive various modifications of the illustrated embodiment and other embodiments of the invention. Therefore, it is to be understood that the appended claims are intended to cover such modifications as would fall within the scope of the invention.

 The following items are further disclosed in connection with the above description.

(1) In a voltage controlled oscillator circuit having a tank circuit for generating vibration, means for setting a constant bias voltage with respect to the ground at the bias side end of the tank circuit, and a gain of the tank circuit Means for sensing a voltage from the alternating voltage side end of the tank circuit so as to control
A capacitor coupled to the AGC capacitor and
A constant current source for supplying a constant charge current to the GC capacitor; and means for discharging the AGC capacitor when the oscillation of the tank circuit exceeds a voltage level determined by a resistance ratio, an emitter-base ratio of a transistor and a power supply voltage. And a voltage controlled oscillator circuit having:

(2) In the voltage controlled oscillator circuit described in item 1,
A current mirror having a transistor connected to the reference voltage line, a ground from the reference voltage line, and passing a constant current to the ground; a collector connected to the bias side end; Is composed of a reference setting transistor connected to a reference line, and a resistor chain connected to the reference line from the bias side end, and the base of the reference setting transistor is connected to a preselected point of the resistance chain. Connected to set the voltage selected for the reference line, and furthermore, whenever the voltage at the alternating voltage side end of the tank exceeds the reference voltage by a predetermined amount, at any time. A voltage controlled oscillator circuit having means for passing current from the AGC capacitor.

(3) In the voltage controlled oscillator circuit described in item 1,
The means for passing current includes a pair of differentially connected transistors, the emitters of which are commonly connected to a constant current source, the collector of a first transistor is connected to an alternating voltage side end of the tank, and The base is connected to its constant bias end, the second transistor has its base connected to the alternating voltage end, the collector is connected to the high voltage source, and the second transistor has a magnitude corresponding to the voltage across the AGC capacitor. A voltage controlled oscillator circuit having means for passing an emitter current having the same from the differential transistor pair.

(4) In the voltage controlled oscillator circuit described in the item (3),
The emitter current passing means includes a diode-connected transistor, a resistor connected between a high voltage source and ground and an emitter-base path of the AGC transistor, and a collector connected to the emitter of the differentially connected pair of transistors. A voltage controlled oscillator circuit having a current mirror having a transistor connected to ground and having a base connected to the base of the diode-connected transistor.

(5) In a voltage controlled oscillator circuit having a tank circuit for generating vibration, a fixed voltage with respect to the ground is connected to the ground side from the bias side end of the tank circuit. A diode assembly for setting the bias point of the AGC capacitor; and an AGC capacitor coupled to the oscillating end of the tank circuit for controlling the gain of the tank circuit for a selected half cycle. A current sink circuit for drawing a current having a magnitude related to the voltage across the tank circuit from the tank circuit; a resistor chain coupled to an AGC capacitor for setting a reference voltage substantially independent of the parameters of the active device; and Coupled to a voltage and an AGC capacitor, and operative to discharge the AGC capacitor when the tank circuit voltage exceeds a predetermined value related to the reference voltage. With a discharge transistor
A voltage controlled oscillator circuit having an AGC discharge circuit.

(6) In the voltage controlled oscillator circuit described in item 5,
The AGC discharge circuit has a reference voltage line, a transistor connected to ground from the reference voltage line, a transistor that passes a constant current to ground, a collector connected to the bias side end, and an emitter connected to the reference line. A reference setting transistor, and a resistor chain connected to the reference line from the bias side end, the base of the reference setting transistor being connected to a preselected point of the resistor chain, A current mirror for setting a voltage selected as a reference line, and means for passing current from the AGC capacitor at any time when a voltage at an alternating voltage side end of the tank circuit exceeds the reference voltage by a predetermined amount. A voltage controlled oscillator circuit including:

(7) In the voltage controlled oscillator circuit described in item 5,
The current sink circuit includes a pair of differentially connected transistors, the emitters of which are commonly connected to a constant current source, and
The collector of the transistor is connected to the terminal on the alternating voltage side of the tank circuit, the base is connected to the terminal on the constant bias side, the base of the second transistor is connected to the terminal on the alternating voltage side, and the collector is connected. A voltage controlled oscillator circuit connected to a high voltage source and further comprising means for extracting, from the differential pair of transistors, an emitter current having a magnitude related to a voltage across the AGC capacitor.

(8) In the voltage controlled oscillator circuit described in the paragraph (7),
The emitter current sink circuit has a diode-connected transistor, a resistor connected between a high voltage source and ground, an emitter-base path of an AGC transistor, and a collector connected to the emitters of the pair of differentially connected transistors. A voltage controlled oscillator circuit including a transistor having an emitter connected to ground and a base connected to the base of the diode-connected transistor.

(9) A voltage-controlled oscillator circuit having a tank circuit for generating vibration is provided at a bias-side end of the tank circuit with a means for setting a constant bias voltage with respect to the ground and for controlling the tank gain. Means for drawing current from the alternating voltage end of the tank; and an AGC capacitor. A constant current source is coupled to the AGC capacitor and provides a constant charging current to the capacitor. Means are provided for discharging the AGC capacitor at a voltage level determined by the resistance ratio and the emitter-base ratio of the transistor.

[Brief description of the drawings]

 FIG. 1 is a circuit diagram of a preferred embodiment of the present invention. Explanation of main symbols 10: Coil 12, 14: Capacitor 50, 52, 54: Transistor of diode connection 60, 62: Transistor of differential pair 66, 70, 74, 78, 80, 86, 88: Transistor 100: AGC Capacitor

Continued on the front page (72) William H. Inventor. Giorma Dating in Dallas, Texas, United States 10105 (72) Inventor Richard Bowshire 715 Fairlane Avenue, Santa Clara, California, United States 715 (56) References JP-A-61-240704 (JP, A) (58) Int.Cl. ⁶ , DB name) H03B 5/00-5/16

Claims (1)

(57) [Claims] An oscillator circuit having a variable gain tank circuit and having a tank circuit that generates vibration having an amplitude proportional to the gain of the tank circuit, wherein a ground terminal is provided at a bias terminal of the tank circuit. Means for setting a constant bias voltage with respect to: means for sensing the amplitude of oscillations generated by the tank circuit at the other end of the tank circuit; an automatic gain control (AGC) capacitor; A constant current source for supplying a constant charging current to the AGC capacitor; and an alternating voltage of the tank circuit, which is coupled to the sensing means and sensed by the sensing means, provides a resistance ratio, a transistor emitter-base ratio, and a power supply. Means for discharging the AGC capacitor when a voltage level determined by a voltage is exceeded, the AGC capacitor being coupled to the tank circuit,
Means for changing the gain of the tank circuit depending on the charge of the GC capacitor.