JPS61141218A - Voltage controlled oscillator - Google Patents

Abstract

PURPOSE:To obtain an excellent linearity by providing a distortion correction circuit comprising a simple circuit to a signal input section of a VCO so as to correct the amplitude component of nonlinear distortion. CONSTITUTION:The distortion correction circuit consists of a transistor amplifier circuit with variable gain having a resistor circuit comprising parallel connection of a resistor RE0 to a series circuit comprising diodes D1-D4 and resistors RE1-RE4. The distortion correction circuit is provided to a signal input section of an emitter coupling multivibrator type VCO1. Then the amplitude component of the non-linear distortion is corrected by selecting properly bias voltages V1-V4 for the resistors RE1-RE4 and the diodes D1-D4. Thus, the characteristic of the VCO with excellent linearity is attained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is applicable to FMg modulators, frequency synthesizers, and phase locked loops (PLLs).
) 7! : Voltage-controlled oscillators used in the field of communications and control equipment engineering, especially voltage-controlled oscillators that include a correction circuit that performs distortion correction for non-linear C2.

[Conventional technology]

Conventionally, this type of voltage controlled oscillator (VCO) has been used, for example, in an FM modulator.
olledQzaillator) is characterized by the output signal frequency jeS with respect to the input signal voltage Winl2.
The characteristics are required to be linear over a wide range as shown in Figure 4. However, in reality, (: is 4 non-linear as shown in FIG. 5C2, and the linear region is limited.

[Problem that the invention seeks to solve]

When a conventional voltage controlled oscillator is used as, for example, an FM modulator, the demodulated signal ζ2 will include nonlinear distortion. In video signal transmission, differential gain (DG) increases and becomes a factor in deteriorating video quality (chroma). This example is shown diagrammatically (2! IP16 Figure C2. The differential gain (DG) is 15
．． 5-58MHz (0-I V
pp ) is defined as the amount of deviation of the amplitude of the color subcarrier from the reference level, and the amplitude component C of the nonlinear distortion is divided into two pairs.

knax-Asxle In the example of FIG. 6, the differential gain DG is indicated by DG-4.

[Means for solving problems]

In order to eliminate the drawbacks of the conventional magnetic pressure control oscillator C2, which has poor linearity, the present invention uses a series body in which a diode and a resistor are connected in series. Connect multiple resistors in parallel, and also connect other resistors (
; Constructs a distortion correction circuit consisting of a variable gain transistor amplifier circuit using a parallel-connected resistor circuit as an emitter resistor;
The present invention is characterized in that this distortion correction circuit is divided into two signal input sections C of the voltage controlled oscillator.

[Effect]

The present invention provides a voltage controlled oscillator with good linearity by providing a distortion correction circuit with a simple circuit configuration at the signal input section of the voltage controlled oscillator (secondly, correcting the amplitude component of nonlinear distortion). This will be explained in more detail from FIG. C2.

〔Example〕 FIG. 1 shows an embodiment of a distortion correction circuit according to the present invention. show.

Diodes D and D are V□ and V!, respectively. The voltage of the transistor Tr2 is biased, and the emitter and collector resistances of the transistor Tr2 are 81'±8('), so the transistor Tr2 is simply a transistor for polarity inversion. In this case, the gain of the circuit is given by .

However, the transistor T that forms the transistor amplifier circuit
The emitter resistance R1 of rl is a diode D.

is on and diode D is off, R1-(Ex
a″″’ + Rx1) s Number of diode stages and both (R, M E, o when there are two diodes, R, m when diode D1 is off and diode D! is on)
R.

♀Rxz-')-'. Therefore, the input signal voltage C
;The gain decreases accordingly. Bias voltage jl −Vt
If an appropriate voltage C is set in two branches as t'i't< Vt, then the input signal voltage V1 (the input/output characteristics of the output signal voltage Votbt for the two?) as shown in the figure 's2 is obtained. , D, direction C; therefore, the direction of the unevenness (characteristic curve in FIG. 2) can be changed. Further, the magnitude of the distortion correction amount can be changed by the magnitude C2 of the resistors RJ1 and R12. Note that the diode D1
．． Since the voltage-4 current characteristics (switching characteristics) of D are exponential, the switching is smooth to some extent C
: occurs, so the correction curve can also be made smooth (;

FIG. 5 shows an embodiment of the voltage controlled oscillator of the present invention using the distortion correction circuit shown in FIG.

In this example, the original distortion characteristic C (in addition, the number of diode stages is increased (4 stages in this example)), the resistor R11v R
J2 s Rls e R14 and bias voltage V1 e
By selecting an appropriate value of Vt e Ya #I'4 k, linearity characteristics as shown in Figure 4 can be obtained. 1-2 This is an example in which the distortion correction circuit according to the present invention (2) is applied. VCt is the control voltage.

As is clear from this example, the amplitude component of the nonlinear distortion of the voltage controlled oscillator is corrected in C2, and the characteristics of the voltage controlled oscillator with good linearity are obtained. Improvements will be made.

〔Effect of the invention〕

As described above, according to the present invention, by providing a distortion correction circuit with a simple circuit configuration in the signal input section of a voltage controlled oscillator, the linear region of the output frequency characteristic with respect to the input signal voltage (2) of the voltage controlled oscillator is Therefore, since there is no non-linear distortion, when the voltage controlled oscillator of the present invention is used for video transmission by FM, for example, the differential gain (in this case, the saturation evaluation measure) is Significantly improved t: Also phase-locked loop (PLL)
Control circuits such as (2) using the voltage controlled oscillator of the present invention have great effects such as improving the linear response of the system.

[Brief explanation of drawings]

FIG. 1 shows an embodiment of the distortion correction circuit according to the present invention, FIG. 2 shows the input signal voltage versus output signal voltage characteristic of the distortion correction circuit C2 of FIG. Example,
i'! Figure 4 shows the input signal voltage vs. output signal frequency characteristics required for a normal voltage controlled oscillator, Figure 5 shows the input signal voltage vs. output signal frequency characteristics of an actual voltage controlled oscillator, and Figure 6 shows the conventional voltage controlled oscillator. C: is a diagram illustrating the state of included nonlinear distortion when used in an FM modulator. Vcc・1. Power supply voltage, Trl, Tr2...transistor, DhD2. D,, D4...diode, v
l, v, , v, , v, , . Bias voltage, RJ1vR□2. R,,,R,4,R
□. vRXvRc', Resistance, Vast... Output signal voltage, Vd... Control voltage, 1... Emitter-coupled multivibrator type voltage controlled oscillator

Claims (1)

[Claims of Claims] A variable gain voltage controlled oscillator, wherein the signal input section of the voltage controlled oscillator is provided with a resistor circuit including a plurality of series bodies each having a diode and a resistor connected in series, and a resistor connected in parallel as an emitter resistor. A voltage controlled oscillator characterized in that it is equipped with a distortion correction circuit consisting of a transistor amplifier circuit.