JP3348403B2 - Oscillator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[Table of Contents] The present invention will be described in the following order. Industrial Application Conventional Technology (FIG. 7) Problems to be Solved by the Invention Means for Solving the Problems (FIGS. 2 and 3) Function (FIGS. 4 to 6) Example (FIGS. 1 to 6) (1) First Embodiment (FIGS. 1 and 2) (1-1) Overall Configuration (FIG. 1) (1-2) Configuration of Local Oscillator Circuits 12D and 14D (FIG. 2) (2) Second Embodiment Example (FIGS. 3 to 6) (3) Other Embodiment Effects of the Invention

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an oscillating device, and is suitably applied to a device requiring stable oscillation over a wide band, such as an oscillator of a television broadcast receiving device.

[0003]

2. Description of the Related Art Generally, a tuner selects a desired high-frequency signal of a channel from a plurality of high-frequency signals induced by an antenna, and then changes the frequency of the selected high-frequency signal to an intermediate frequency (58.75 [MHz]). Today, the lower limit is about 50 MHz of the VHF band and the upper limit is UH
It covers a wide band up to about 900 [MHz] of the F band.

For this reason, a local oscillation circuit for converting a selected high-frequency signal into an intermediate frequency is required to oscillate stably over a wide band in accordance with these received signals. There is a configuration as shown in FIG.

Here, the local oscillation circuit 1 generates a local oscillation output S
1 and a differential buffer amplifier stage 3 commonly connected at the base to the differential amplifier stage 2 for generating an oscillation signal, and the collector output of the buffer amplifier stage 3 is locally oscillated. The output S1 is supplied to a mixer.

The oscillation differential amplifier stage 2 is composed of a pair of transistors Q1 and Q2, and a constant current source 2A for drawing a constant current (5 [mA]) to a common emitter.
Is connected.

The resonance circuit 4 is connected to the collector of the transistor Q1 via a coupling capacitor C1. The oscillation output of the resonance circuit 4 is positively fed back to the base of the transistor Q2 via a feedback capacitor C2, and has a predetermined frequency. Is supplied to a buffer amplifier stage 3 comprising a differential pair of transistors Q3 and Q4.

The resonance circuit 4 includes a coil L1 and a variable capacitor C3. The oscillation range can be continuously variably controlled by changing the capacitance of the variable capacitor C3. I have.

In the oscillation differential amplifying stage 2, the base of the transistor Q1 is AC grounded via a capacitor C4, and the other end is connected to the connection point between the collector of the transistor Q1 and the coupling capacitor C1. A coil L2 to which a DC power supply V1 is supplied is connected so that a high-frequency oscillation output does not affect the power supply.

On the other hand, the bases of the transistors Q3 and Q4 constituting the buffer amplifier stage 3 are connected to the bases of the transistors Q2 and Q1 of the differential amplifier stage 2 for oscillation, respectively. [MA])
Is connected.

As a result, the buffer amplifier stage 3 inputs the oscillation output generated by the oscillation differential amplifier stage 2 and a predetermined voltage as differential inputs, and the diodes D1 and D2 connected to the collectors of the transistors Q3 and Q4. Are output as local oscillation outputs S1 from the connection middle point.

The transistors Q1 and Q2 forming a differential pair
And the base potentials of Q4 and Q3 are the direct current sources V
2 is adjusted by the resistance values of the resistors R1 and R2 connected to the resistor R2.

[0013]

However, in the case of the local oscillation circuit 1, when the input capacitance is viewed from the resonance circuit 2A, the parasitic capacitance Cπ (Q
2) and Cπ (Q3) appear in parallel to the resonance circuit 2A, so that the input capacitance has to be increased.

As described above, if the input capacitance is large, the capacitance change ratio of the variable capacitor C2 formed of a varicap diode used to vary the oscillation frequency becomes apparently small, so that the variable range of the oscillation frequency cannot be increased. .

The present invention has been made in view of the above points, and an object of the present invention is to propose an oscillation device that can further expand the adjustment range of the oscillation frequency with a simple configuration as compared with the related art.

[0016]

According to the present invention, a first and second transistors Q1 and Q2 forming a differential pair and a common emitter of the first and second transistors Q1 and Q2 are provided. Connected to the base of the second transistor Q2 via the resonance means 4 to provide a positive feedback signal to the base of the first transistor Q1. Oscillating circuit 2 oscillating at a predetermined frequency and outputting a positive feedback signal as an oscillation output; third and fourth transistors Q21 and Q22 forming a common-collector type differential amplification stage; A second constant current source 21A connected to a common emitter of the transistors Q21 and Q22, the base of the first transistor Q1 and the fourth transistor Q2;
22, the base of the second transistor Q2 and the base of the third transistor Q21 are connected, and the oscillation output is connected to the third and fourth transistors Q21.
And a buffer circuit 2 for differentially amplifying the signals received by the bases of the transistors Q21 and Q22 and outputting the amplified signals as first and second differential outputs from the emitters of the third and fourth transistors Q21 and Q22.
1, the current value of the second constant current source 21A is smaller than the current value of the first current source 2A.

Further, in the present invention, the first and second transistors Q1 and Q2 forming a differential pair and the first constant current source 2A connected to the common emitter of the first and second transistors Q1 and Q2. And oscillates at a predetermined frequency by connecting the collector of the first transistor Q1 to the base of the second transistor Q2 via the resonance means 4 and applying a positive feedback signal to the base to generate a positive feedback signal. An oscillator circuit 2 for outputting an oscillation output, third and fourth transistors Q21 and Q22 forming a common-collector type differential amplifier stage, and a common emitter of the third and fourth transistors Q21 and Q22 are connected. Second constant current source 2
1A, the base of the first transistor Q1 and the fourth
And the base of the second transistor Q2 and the third transistor Q22.
21 and connected to the base of the third and fourth transistors Q21 and Q22 to differentially amplify the oscillating output, and the third and fourth transistors Q21 and Q22
A first buffer circuit 21 for outputting the first and second differential outputs from the emitter side of the first and second and fifth and sixth transistors Q3 and Q4 forming an emitter-grounded differential amplifier stage. And the second differential output are respectively connected to the fifth and sixth differential outputs.
Of the transistors Q3 and Q4
A second buffer circuit 3 that outputs third and fourth differential outputs from the collectors of the fifth and sixth transistors Q3 and Q4, and sets the current value of the second constant current source 21A to the first. Is smaller than the current value of the current source 2A.

[0018]

[0019]

A buffer circuit 21 comprising a grounded collector type differential amplifier stage is connected to the oscillating circuit 2, and the third and fourth transistors Q21 and Q22 forming the buffer circuit 21 are connected.
The current value of the second constant current source 21A connected to the common emitter of the first constant current source 2A connected to the common emitter of the first and second transistors Q1 and Q2 forming the oscillation circuit 2. By making it smaller than the current value, the first
In addition, the capacitance of the second transistors Q1 and Q2 themselves can be reduced to reduce the parasitic input capacitance in the feedback path, and the oscillation frequency range of the oscillation means 4 can be further expanded as compared with the conventional case.

Further, by outputting the oscillation output of the oscillation circuit 2 to the subsequent stage through the first and second buffer circuits 21 and 3, the degree of separation between the oscillation circuit 2 and the circuit at the subsequent stage can be improved. In addition, it is possible to further reduce the intermodulation caused by the oscillation circuit 2 receiving the modulation and the fluctuation of the oscillation state caused by the signal sneaking from the subsequent circuit as compared with the related art.

[0021]

[0022]

BRIEF DESCRIPTION OF THE DRAWINGS FIG.

(1) First Embodiment (1-1) Overall Configuration In FIG. 1, reference numeral 10 denotes a television signal receiving apparatus as a whole, and a VHF antenna 1 is provided by a VHF antenna 11.
2. The video intermediate frequency amplified signal S1 converted to the intermediate frequency via the UHF antenna 2 or the UHF tuner 1 from the UHF antenna 13.
The video intermediate frequency amplified signal S2 converted to the intermediate frequency via the input terminal 4 is input from the output switching circuit 15 to the intermediate frequency amplification circuit 16, and the intermediate frequency signal amplified in the intermediate frequency amplification circuit 16 is output from the output terminal to the video detection circuit. Output.

Here, the VHF tuner 12 inputs the high-frequency signal RF1 received by the VHF antenna 11 via the input impedance matching input circuit 12A to the high-frequency amplifier circuit 12B, and selects the desired high-frequency signal of the channel. It is amplified and supplied to the mixer 12C. This mixer 1
2C multiplies the high-frequency signal of the desired channel amplified by the high-frequency amplifier circuit 12B by the oscillation output supplied from the local oscillation circuit 12D, and converts the multiplied signal into an intermediate frequency signal S1.

On the other hand, the UHF tuner 14 has the same configuration as the VHF tuner 12, and the high frequency signal of the desired channel amplified through the input circuit 14A and the high frequency amplifier circuit 14B and the oscillation output provided by the local oscillation circuit 14D. Is multiplied by the mixer 14C to convert it into an intermediate frequency signal S2.

(1-2) Local oscillation circuits 12D and 14D
In FIG. 2, in which parts corresponding to those in FIG. 7 are assigned the same reference numerals, local oscillation circuits 12D and 14D connect emitter follower input stages 17A and 17B to the bases of transistors Q1 and Q2 of oscillation differential amplifier stage 2. It has the same configuration except that it does.

Here, the emitter follower input stages 17A and 17B are composed of transistors Q11 and Q12, respectively.
1 and Q2 have transistors Q11 and Q12
Emitters are connected.

The emitters of the transistors Q11 and Q12 are connected to constant current sources 18A and 18B for drawing a constant current of 1 mA, respectively. At this time, the parasitic capacitance Cπ (Q
12) is apparently connected in series to the parasitic capacitances Cπ (Q2) and Cπ (Q3) parasitic to the transistor Q2 of the oscillation differential amplifier stage 2 and the transistor Q3 of the buffer amplifier stage 3.

As a result, the combined parasitic capacitance can be apparently reduced as compared with the conventional case, and the variable range of the oscillation frequency by the variable capacitor C2 can be widened.

In the above configuration, the local oscillation circuit 12D
And 14D make the oscillation output of the oscillation differential amplifying stage 2 positively fed back to the base of the transistor Q2 forming a differential pair via the transistor Q12 of the emitter follower input stage 17B to oscillate.

At this time, the input capacitance Cπ viewed from the resonance circuit 4
Is

(Equation 1) Given by In the case of this embodiment, the parasitic capacitances Cπ (Q2) and Cπ
The magnitude of the parasitic capacitance Cπ (Q12) of the transistor Q12, which is parasitic in series with (Q3), is about 1.6 because the constant current flowing through the constant current source 18B is as small as 1 [mA].
[PF].

As a result, the combined input capacitance Cπ is 5.3 [p
F], which is smaller than that of the conventional local oscillation circuit 1. As a result, the variable capacitance of the variable capacitor C3 can be changed within a range of about 1.5 times as compared with the conventional case, and the oscillation frequency adjustment range can be further expanded as compared with the conventional case.

According to the above configuration, the magnitude of the input capacitance Cπ as viewed from the input terminal P3 among the input capacitances parasitic on the resonance circuit 4 can be further reduced as compared with the related art.
The variable range of the oscillation frequency by the variable capacitor C3 can be further expanded as compared with the related art.

(2) Second Embodiment In FIG. 3, in which parts corresponding to those in FIG. 2 are assigned the same reference numerals, reference numeral 20 denotes a local oscillator circuit in the television signal receiver as a whole, and a differential amplifier for oscillation. It has a similar configuration except that an emitter-follower type differential buffer amplifier stage 21 is provided between the stage 2 and the buffer amplifier stage 3.

Here, the differential buffer amplifier stage 21 inputs the differential output of the oscillation differential amplifier stage 2 to the transistors Q21 and Q22. At this time, the emitters of the transistors Q21 and Q22 are connected to the load resistors R21, R22 and R23, R2.
The differential output of the differential buffer amplifier stage 21 is output to the buffer amplifier stage 3 from the connection point between the load resistors R21 and R22, R23 and R24.

The load resistors R21 and R23 prevent the parasitic oscillation caused by the emitter follower amplifier stage, and the transistors Q21 and Q3 viewed from the connection terminals P1 and P3.
The impedance of 22 is made to look high apparently.

Load resistors R25 and R26 are connected to the collectors of the transistors Q21 and Q22, and the oscillation output OS2 appearing at the load resistors R25 and R26 is output to the PL.
Output is made for an L (phase locked loop) circuit. By extracting the oscillation output OS2 in this manner, leakage of a high-frequency signal can be reduced, and even when a high-amplitude high-frequency signal is input, malfunction of the PLL circuit due to the high-frequency signal can be reduced.

In the above configuration, the local oscillation circuit 20 applies the oscillation output from the oscillation differential amplifier stage 2 to two buffer amplifier stages, that is, an emitter follower type differential buffer amplifier stage 21 and a buffer amplifier stage 3 sequentially. Mixer 12
C and 14C, and multiplies the oscillation output by the high-frequency signal received by the VHF antenna 11 or the UHF antenna 13 to convert the high-frequency signal of the selected channel into an intermediate-frequency signal.

At this time, the oscillation differential amplifier stage 2 and the mixer 12
Since C (14C) is connected via a two-stage buffer, the high-frequency signal flowing from the mixer is reduced. As a result, the cross-modulation distortion caused by the oscillation signal being modulated by the interfering wave is reduced even though the signal is originally unmodulated, and the inter-modulation distortion particularly in the high frequency band is improved as shown in FIG. Will be.

At this time, the input impedance Z _{IN as} seen from the connection terminal P3 is substantially determined by the capacitance between the base emitters (ie, the diffusion capacitance) of the transistor. In general, the diffusion capacitance tends to decrease as the transition frequency f _T increases, and increase as the current flows.

In this embodiment, the transition frequency f
_{When T} is 5 [GHz], each transistor Q1 of the oscillation differential amplifier stage 2 through which a common emitter current of 5 [mA] flows.
And the diffusion capacitance parasitic to Q2 is about 3 [pF].

On the other hand, the transistors Q21 and Q22 of the differential buffer amplifier stage 21 constituting the first buffer amplifier stage.
Since only a current of about 2 [mA] flows as a common emitter current, the diffusion capacitance is as small as 1 [pF]. Further, since voltage divider resistors R21 and R23 are respectively connected to the emitter, the input of transistors Q21 and Q22 is The impedance can be neglected (FIG. 5).

As a result, the input impedance of the local oscillation circuit 20 becomes 1.5 [pF], whereas in the case of the conventional local oscillation circuit 1, the buffer amplifier stage 21
Also, a constant current of 5 mA flows as a common emitter current, and the diffusion capacitance of the transistors Q3 and Q4 forming a differential pair is seen. Therefore, the input capacitance is 3 [pF], and the input capacitance can be reduced to half that of the conventional case.

As a result, the input impedance of the local oscillation circuit 20 is twice that of the conventional case, and the load Q value of the resonance circuit is as shown by the solid line in FIG. 6 as compared with the conventional case (shown by the broken line in FIG. 6). Get higher.

As described above, when the load Q of the resonance circuit is high, the oscillation stability is improved. Therefore, it is possible to reduce the drift of the oscillation frequency that occurs when the power supply voltage fluctuates or immediately after the power supply is turned on. It is possible to prevent the oscillation frequency from shifting, the oscillation from jumping, and the oscillation from being stopped.

According to the above configuration, the resonance circuit 4 and the mixers 12C and 1C are provided via the two buffer amplification stages 21 and 3.
4C, the separation characteristics between the two circuits can be improved as compared with the prior art, and cross-modulation due to the modulation of the resonance circuit itself and oscillation failure due to the large-amplitude high-frequency signal wrapping around the resonance circuit side. Stability can be lost.

The common emitter current flowing in the emitter-follower type differential amplifier stage 21 connected in parallel to the oscillation differential amplifier stage 2 is input to the resonance circuit 4 by the common emitter current flowing in the preceding oscillation differential amplifier stage 2. By reducing the capacitance and increasing the load Q of the resonance circuit 4, the variable range of the oscillation frequency can be expanded as compared with the conventional case, and the amount of frequency shift immediately after turning on the power can be eliminated.

(3) Other Embodiments In the above-described embodiment, the oscillation circuit is shown in FIGS.
However, the present invention is not limited to this, and a differential Colpitts oscillation circuit may be used.

In the above-described embodiment, the case where the resonance circuit is shown in FIGS. 2 and 3 has been described. However, the present invention is not limited to this, and a resonance circuit having another configuration may be used.

Further, in the above-described embodiment, the case where the present invention is applied to a local oscillation circuit in a television signal receiving apparatus has been described. However, the present invention is not limited to this, and oscillation in which stable oscillation is required over a wide band is required. It can be widely applied to circuits.

Further, in the above-mentioned embodiment, a current of 5 [mA] is supplied to a current source connected to a common emitter of the transistors Q1 and Q2 constituting the oscillation differential amplifier stage 2, and an emitter follower type differential amplifier stage is provided. Each of the current sources connected to the emitters 17A, 17B and 21 has one
Although the case where the currents of [mA] and 2 [mA] are applied has been described, the present invention is not limited to this, and it is sufficient that the current flowing in the buffer amplifier stage is smaller than the current flowing in the oscillation circuit.

[0052]

As described above, according to the present invention, a buffer circuit composed of a common-collector type differential amplifier stage is connected to an oscillation circuit, and a common emitter of the third and fourth transistors constituting the buffer circuit is connected. The current value of the second constant current source connected to the first and second transistors is smaller than the current value of the first constant current source connected to the common emitter of the first and second transistors forming the oscillation circuit. The input capacitance parasitic on the feedback path can be reduced by reducing the capacitance of the first and second transistors themselves, and the oscillating frequency range of the oscillating means can be further expanded as compared with the related art. Further, by outputting the oscillation output of the oscillation circuit to the subsequent stage through the first and second buffer circuits, the degree of separation between the oscillation circuit and the subsequent stage circuit can be improved, and the oscillation circuit can be modulated. Therefore, fluctuations in the oscillation state due to cross-modulation due to signals and a signal sneaking around from a subsequent circuit can be further reduced as compared with the related art.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an overall configuration of a television signal receiving device using an oscillation device according to the present invention.

FIG. 2 is a connection diagram showing one embodiment of a local oscillation circuit according to the present invention.

FIG. 3 is a connection diagram showing another embodiment.

FIG. 4 is a characteristic curve diagram for explaining cross modulation distortion.

FIG. 5 is a schematic connection diagram for explaining a reduction in input capacitance as viewed from a resonance circuit.

FIG. 6 is a characteristic curve diagram for explaining a change in a load Q of a resonance circuit.

FIG. 7 is a connection diagram for describing a conventional local oscillation circuit.

[Explanation of symbols]

10 television signal receiving device, 12, 14 ... tuner, 12A, 14A ... input circuit, 12B, 14B
... High frequency amplifier circuit, 12C, 14C ... Mixer, 12
D, 14D: local oscillation circuit, 15: output switching circuit,
16 ... Intermediate frequency amplifier circuit.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-56-147502 (JP, A) JP-A-57-207358 (JP, A) Jikai 49-145554 (JP, U) (58) Field (Int.Cl. ⁷ , DB name) H03B 5/00-5/28 H04B 1/26

Claims (3)

(57) [Claims] 1. A first transistor comprising a differential pair of first and second transistors and a first constant current source connected to a common emitter of the first and second transistors. An oscillation circuit which oscillates at a predetermined frequency by applying a positive feedback signal to the base of the second transistor via a resonance means and applies a positive feedback signal to the base, and outputs the positive feedback signal as an oscillation output; The first and fourth transistors forming a grounded differential amplifier stage and a second constant current source connected to a common emitter of the third and fourth transistors .
Base of the fourth transistor and base of the fourth transistor.
And the base of the second transistor.
Connecting the base of over scan and the third transistor, the oscillation output by receiving the base of the third and the fourth transistor and the differential amplifier, the emitter side of the third and fourth transistors An oscillation device comprising: a buffer circuit that outputs first and second differential outputs; wherein a current value of the second constant current source is smaller than a current value of the first current source. 2. The first transistor according to claim 1, further comprising: a first transistor and a second transistor forming a differential pair; and a first constant current source connected to a common emitter of the first and second transistors. An oscillation circuit which oscillates at a predetermined frequency by applying a positive feedback signal to the base of the second transistor via a resonance means and applies a positive feedback signal to the base, and outputs the positive feedback signal as an oscillation output; The first and fourth transistors forming a grounded differential amplifier stage and a second constant current source connected to a common emitter of the third and fourth transistors .
Base of the fourth transistor and base of the fourth transistor.
And the base of the second transistor.
Connecting the base of over scan and the third transistor, the oscillation output by receiving the base of the third and the fourth transistor and the differential amplifier, the emitter side of the third and fourth transistors A first buffer circuit for outputting as first and second differential outputs; and a fifth and sixth transistor forming an emitter-grounded differential amplifier stage, wherein the first and second differential outputs are provided. And a second buffer circuit for receiving and amplifying the signals at the bases of the fifth and sixth transistors, respectively, and amplifying the amplified signals, and outputting as third and fourth differential outputs from the collectors of the fifth and sixth transistors. An oscillation device, wherein a current value of the second constant current source is smaller than a current value of the first current source. 3. The first buffer circuit according to claim 1, wherein said first and second differential outputs are connected via first and second voltage dividing resistors respectively connected to emitters of said third and fourth transistors. 4. The oscillation device according to claim 3, wherein the voltage is divided into a predetermined level and output.