JPH0335605A - Voltage controlled oscillator - Google Patents

Abstract

PURPOSE:To obtain an oscillation output without being affected by means of the fluctuation of an element and a temperature change by changing the phase difference of two oscillation outputs at about 90 deg. and feeding back the phase error signal of both oscillation outputs to a phase shift circuit. CONSTITUTION:The output of a crystal resonator 110 being a signal source is inputted to the phase shift circuit 135 consisting of a resistor R12 and a capacitor C12, both of which are connected in serial between the resonator and a ground terminal. A differential amplifier 137 consists of transistors 118 and 119 and a constant current source 125 connected between an emitter to which said transistors are commonly connected and ground. A differential amplifier 138 consists of transistors 116 and 117 and a constant current source 123 connected between an emitter to which said transistors are commonly connected and ground. An input signal for the phase shift circuit 135 is inputted to the base of the transistor 119 through an emitter follower circuit consisting of transistors 114 and 126.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a voltage controlled oscillator whose oscillation frequency is changed by an external control signal, and particularly relates to a voltage controlled oscillator with a phase difference of 90'.
This invention relates to a voltage controlled oscillator that obtains two oscillation outputs.

[Prior Art] Conventionally, a circuit shown in FIG. 2 is known as a voltage controlled amplifier used in, for example, a QPSK demodulation circuit for a BS tuner, and which obtains an oscillation output with a phase difference of 90°.

The output of the crystal oscillator 228, which is a signal source, is connected to a resistor R2 connected in series between the crystal oscillator 228 and the ground terminal.
A first phase shift circuit 235 consisting of □ and capacitor C2□
has been entered.

On the other hand, a constant current source 2 connected between the transistors 218 and 219 and their commonly connected emitters and ground.
25 constitutes a first differential amplifier, and transistor 2
18 and 217 and a constant current source 223 connected between their commonly connected emitters and ground, forming a second differential amplifier.

An input signal to the phase shift circuit 235 is input to the base of the transistor 219 of the first differential amplifier via an emitter follower circuit consisting of a transistor 215 and a constant current source 226. Further, the output signal from the phase shift circuit 235 is biased by a constant voltage source 221 via a resistor R220, and is passed to the transistor 218 of the first differential amplifier via an emitter follower circuit consisting of a transistor 214 and a constant current source 224. and the base of the transistor 217 of the second differential amplifier.

Further, a bias voltage from a constant voltage source 221 is applied to the base of the transistor 216 of the second amplifier circuit via an emitter follower circuit including a resistor 212, a transistor 213, and a constant current source 222.

The negative phase outputs from the load resistors 205 and 204 of the first and second differential amplifiers are taken out from output terminals 231 and 230, respectively.

The common mode outputs of the first and second differential amplifiers are fed to an adder consisting of transistors 208, 209, 210, and 211. This adder changes the combination ratio of the outputs of the two differential amplifiers based on external control voltages supplied to control terminals 201 and 202. The output of this adder is connected to the resistor 20B, transistor 207 and constant current source 227.
It is taken out from the output terminal 229 via an emitter follower consisting of. This output is input to a second phase shift circuit 236 consisting of a resistor R21 and a capacitor C2□. The output of this second phase shift circuit 236 is the crystal oscillator 228
has been given positive feedback. Note that 203 in the figure is a DC power supply that supplies power to the entire circuit.

The operation of this voltage controlled oscillator will be explained using the vector diagram shown in FIG.

Now, if the output signal of the oscillator taken out from the output terminal 229 is vl, the output signal v2 via the second phase shift circuit 236 is delayed by 45 degrees with respect to the output signal Vl, and is applied to the crystal resonator 228. It will be done. In the crystal oscillator 228,
Due to its phase shift characteristic, the signal is delayed by 45 degrees, for example, and this signal becomes the input signal v3 of the first phase shift circuit 235.

In the first phase shift circuit 235, the input signal v3 is further
A signal v4 delayed by 5'' is output.

Therefore, the transistor 219.21 of the first differential amplifier
8, a signal V:l+V4 delayed by 90'' and 135° from the signal v1 is inputted, respectively. Also, the signal v4 is inputted to the transistor 217 of the second differential amplifier.

The common mode outputs of the first and second differential amplifiers are set to V5+V, respectively.
8. If the gain of these differential amplifiers is A, then these first
and the common mode output VI5+Va of the second differential amplifier are as follows.

V5 = -A (V4 V3) ・”
(1) Ve = AV4 =
(2) The output signal v5 has a phase relationship of -45° with respect to the signal vl, and the output signal V6 has a phase relationship of +45' with respect to the signal Vl.
It has a phase relationship of

These signals are input to an adder, where the control terminal 20
1, 202 at a synthesis ratio based on the external control voltage supplied to the terminals 1 and 202. If the combined signal matches the signal Vl, positive feedback will occur at the resonant frequency of the crystal oscillator 228,
If oscillation occurs and there is a phase difference, the crystal resonator 228
oscillates at a frequency determined by the phase shift characteristics of

Therefore, the output terminals 231 . of the first and second differential amplifiers.
230, two oscillation outputs having a phase difference of 90', V15+ve, can be obtained.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional voltage controlled oscillator, 2
There are problems in that the waveforms of the two oscillation output signals va*-va are distorted and the phase difference between them is not exactly 90°.

The reason for this will be explained below.

That is, the relationship between the input signal v3 and the output signal V4 of the first phase shift circuit 235 is expressed as follows.

R2゜.

1 + j ωC22R220 220 3 R22+ R220+ J (t)C22R22R22
0... (3) Therefore, the following equation (4) holds true.

V! 3 R22+ R220+JωC22R22R2
20V4 R220... (4) Also, from the above-mentioned formulas (1) and (2), the following (5)
The formula holds true.

■5 4 V3 6 4 R2□+jωC2□R2□R2□.

220 220 Therefore, RQ. ) Only if the condition of R2゜0 is satisfied,
V5/V8'F j (IJC22R22, and the phase difference of v6° and v6 becomes a value close to 90'.

However, since R2゜0 is a bias resistance, if this value is made extremely large, DC
An offset will occur and the oscillator output will be distorted.

Furthermore, as is clear from equation (5), the phase difference fluctuates due to variations in resistor and capacitor values, temperature changes, etc., and the phase difference between the two outputs of the voltage controlled oscillator is not exactly 90'. There's a problem.

The present invention has been made in view of such problems, and includes:
It is an object of the present invention to provide a voltage controlled oscillator which can obtain highly accurate oscillation output without distortion of the output waveform and which is unaffected by variations in elements such as resistors and capacitors, temperature changes, etc.

[Means for Solving the Problems] A voltage controlled oscillator according to the present invention includes a signal source, a first phase shift circuit that shifts the phase of an oscillation output signal from the signal source, and a first phase shift circuit that shifts the phase of an oscillation output signal from the signal source. a first differential amplifier having an input signal and an output signal as differential inputs; a second differential amplifier having one input having the output of the first phase shift circuit and having the other input biased; an adder that adds the outputs of the first and second differential amplifiers and changes the combination ratio based on an external control signal; and a second adder that shifts the phase of the output of the adder and feeds it back to the signal source. and a voltage controlled oscillator that changes the frequency by controlling a feedback signal to the signal source using the external control signal, the output of the first or second differential amplifier being a phase shift control input. a third phase shift circuit that changes the phase difference between the outputs of the first and second differential amplifiers in a range including 90' by shifting the phase by a phase shift amount according to the voltage; The phase difference controlled by the circuit is 90″
a phase detector that detects the amount of deviation from the phase error as a phase error;
A low-pass filter that smoothes the phase error output from this phase detector, and a phase error amplifier that amplifies the output of this low-pass filter and outputs it as the phase shift control input voltage to the third phase shift circuit. It is characterized by

[Operation] In the present invention, the output of the first or second differential amplifier is phase-shifted by the third phase shift circuit, so that the phase difference of the re-output is changed around 90 degrees. Then, the phase difference between the two outputs via the third phase shift circuit is detected by a phase detector, and the deviation from 90' is output as a phase error. This output is smoothed by a low-pass filter, amplified by a phase error amplifier, and then given as a phase shift control input voltage to the third phase shift circuit. Thereby, the third phase shift circuit changes the phase shift amount of the output of the first or second differential amplifier so that the phase error is 0, that is, the phase difference is 90'.

This allows the phase difference between the two signals input to the phase detector to be exactly 90'.

[Embodiments] Hereinafter, embodiments of the present invention will be described based on the accompanying drawings.

FIG. 1 is a circuit diagram of a voltage controlled oscillator according to an embodiment of the present invention.

The output of the crystal oscillator 110, which is a signal source, is transmitted through a resistor R, which is connected in series between the crystal oscillator 110 and the ground terminal.
□ and a first phase shift circuit 135 consisting of a capacitor C12
has been entered.

On the other hand, a constant current source 1 connected between the transistors 118 and 119 and their common grounded emitters and the ground.
25 constitutes a first differential amplifier 137, and transistors 116 and 117 and a constant current source 123 connected between their commonly connected emitters and ground constitute a second differential amplifier 138. has been done.

An input signal to the phase shift circuit 135 is input to the base of the transistor 119 of the first differential amplifier 137 via an emitter follower circuit consisting of a transistor 114 and a constant current source 126.

Further, the output signal from the phase shift circuit 135 is output from the constant voltage source 13.
4 via the resistor R14, and the base of the transistor 118 of the first differential amplifier 137 and the transistor 117 of the second differential amplifier 138 via an emitter follower circuit consisting of the transistor 113 and the constant current source 124. is entered on the basis of Further, a bias voltage based on a constant voltage 1li7134 is supplied to the base of the transistor 118 of the second differential amplifier 138 via an emitter follower circuit including a resistor RIG, the transistor 112, and a constant current source 122.

The in-phase outputs of the first and second differential clay pipe widths n137 and 138 are input to an adder consisting of transistors 105, 108 and 107°108. This adder changes the combination ratio of the outputs of the two differential amplifiers 137, 138 based on external control voltages supplied to control terminals 101, 102, respectively. The output of this adder is taken out via an emitter follower consisting of a resistor 103, a transistor 109, and a constant current source 127. This output is connected to the resistor RI
I and a second phase shift circuit 136 consisting of a capacitor C0. The output of this second phase shift circuit 136 is positively fed back to the crystal oscillator 110.

On the other hand, the negative phase output taken out by the load resistor 104 of the first differential amplifier 137 is taken out to the outside via the output terminal 129. Additionally, the second differential amplifier 138
The negative phase output taken out by the load resistor 140 is input to the third phase shift circuit 139 via an emitter follower circuit consisting of a transistor 111 and a constant current source 121.

This phase shift circuit 139 includes a resistor R15 and a capacitor C13.
and a voltage variable capacitance diode C14. The output of this phase shift circuit 139 is taken out from an output terminal 128 via an emitter follower circuit consisting of a transistor 115 and a constant current source 120.

Further, the outputs from the output terminals 128 and 129 are inputted to a phase detector 130 and subjected to phase detection. The phase error output from this phase detector 130 is transmitted to the low-pass filter 1
After smoothing by 31, phase error amplifier 132
and is fed back to the anode side of the voltage variable capacitance diode C14 as a phase shift control voltage.

Note that 133 in the figure is a DC power supply that supplies power to the entire circuit.

Next, the operation of the voltage controlled oscillator configured in this way will be explained.

If the signal input to the second phase shift circuit 136 is Vl, the output signal v2 of the second phase shift circuit 136 is the output signal V
, and is applied to the crystal resonator 110. In the crystal resonator 110, the phase is further delayed by 45° due to the phase shift characteristic, and this signal is input to the first phase shift circuit 135 as the input signal v3. The first phase shift circuit 135 outputs a signal v4 which is obtained by further delaying the input signal v3 by 45''.

Here, the relationship between the input signal v3 and the output signal V4 of the first phase shift circuit 135 is expressed as follows.

14 1+jωC12R+4 RI4°v3 R+2+ R14+ j ωC12R1°R14...
(6) Therefore, the cubic equation (7) holds true.

R1□+R+4+jωC1゜R12R144 R+4... (7) Also, if the gain of the differential amplifier 137.138 is A, then
The output car V51 Ve is expressed as follows.

-V5=A (V4-V3)...
(8)-Ve=AV4・”
(9) Therefore, the following equation (10) holds true.

5 4 Va 6 4 R1□jωC1□R12R14 14 14 Therefore, the phase angle 0 between the signal -V5 and the signal -Ve can be expressed as follows.

θ= −tan−′ωct2R+□+++ (11) Here, ωCl2RI. 〉O, so θ for phase is 0
@ θ<90”.

Therefore, in this circuit, the phase of the signal -VB is shifted by the third phase shift circuit 139, and the amount of phase shift in this phase shift circuit 139 is changed from Oo to α. As a result, the phase difference β between the signal -v7 and the signal -■5 after the phase shift of the signal -■8 becomes θ × β × θ + α, so β is 9
It can take values around 0''.

Therefore, when the phase difference β is larger than 90°, the phase detector 130 outputs a positive phase error output, which is smoothed by the low-pass filter 131, amplified by the phase error amplifier 132, and then output from the voltage variable capacitance diode C1.
4. Raise the potential on the anode side of No.4. As a result, the capacitance of the diode CI4 decreases, the phase of the output of the phase shift circuit 139 advances, and the phase difference β approaches 90°.

When the phase difference β is smaller than 90', a negative phase error output is output from the phase detector 130, smoothed by the low-pass filter 131, amplified by the phase error amplifier 132, and then output from the voltage variable capacitance diode CI.
Lower the potential on the anode side of 4. As a result, the capacitance of the diode CI4 increases, the phase of the output of the phase shift circuit 139 is delayed, and the phase difference β approaches 90'. In other words, the phase shift control voltage and the amount of phase shift have an inversely proportional relationship.

As a result, output terminals 128 and 129 output exactly 90"
It is possible to obtain two oscillation output signals V5+-V7 with a phase difference of .

Note that in the above embodiment, the output voltage V of the second differential amplifier 138. Although the phase of the output signal V5 of the first differential amplifier 137 is shifted by the third phase shift circuit 139, the phase of the output signal V5 of the first differential amplifier 137 may be shifted by the third phase shift circuit 139.

[Effects of the Invention] As explained above, according to the present invention, the phase difference between the two oscillation outputs is changed by around 90° by the third phase shift circuit, and the phase error between the two optical oscillation outputs is reduced. Since the signal is fed back to the third phase shift circuit, it is possible to obtain a highly accurate oscillation output that is unaffected by variations in elements such as resistors and capacitors, temperature changes, and the like.

Furthermore, since the present invention assumes that the third phase shift circuit adjusts the phase difference, it is not necessary to accurately bring the phase difference between the outputs of the two differential amplifiers close to 90". Therefore, the resistance of the bias resistor Since it is not necessary to make the value extremely large, it is possible to prevent DC offset from occurring in the manual operation of the differential amplifier, and it is possible to obtain an output waveform without distortion.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a voltage controlled oscillator according to an embodiment of the present invention, FIG. 2 is a circuit diagram of a conventional voltage controlled oscillator, and FIG. 3 is a vector diagram for explaining the operation of the voltage controlled oscillator. . 101.102, 201, 202; control terminal, 128.
129, 229 to 231; Output Z1a, 130: Phase detector, 131; Low pass filter, 132; Phase error amplifier, 135, 138, 139.235.236;
Phase shift circuit, 137, 138; differential amplifier

Claims (1)

[Claims] (1) A signal source, a first phase shift circuit that shifts the phase of the oscillation output signal from the signal source, and a first phase shift circuit that uses the input signal and output signal of the first phase shift circuit as differential inputs. a differential amplifier;
A second differential amplifier whose one input is the output of the first phase shift circuit and whose other input is biased, and the outputs of the first and second differential amplifiers are added together and the combined ratio is externally It includes an adder that changes the phase based on a control signal, and a second phase shift circuit that shifts the phase of the output of the adder and returns it to the signal source, and the feedback signal to the signal source is adjusted by the external control signal. In the voltage controlled oscillator that changes the frequency by controlling the phase shift control input voltage, the output of the first or second differential amplifier is shifted by a phase shift amount according to a phase shift control input voltage.
and a third phase shift circuit that changes the phase difference between the outputs of the second differential amplifier in a range including 90 degrees, and a third phase shift circuit that changes the amount by which the phase difference controlled by the third phase shift circuit deviates from 90 degrees. a phase detector that detects a phase error; a low-pass filter that smoothes the phase error output from the phase detector; and a low-pass filter that amplifies the output of the low-pass filter and supplies the phase shift control input voltage to the third phase shift circuit. 1. A voltage controlled oscillator comprising: a phase error amplifier that outputs a phase error amplifier;