JPS6322082B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a modulator, which supplies a modulation signal passed through a low-pass filter to each base of a pair of transistors, and has a collector connected to a common emitter of the pair of transistors. By supplying a carrier wave to the base of the current operation transistor, it is possible to sufficiently suppress the carrier wave signal component of the modulated wave, especially in the high frequency band, and to sufficiently suppress spurious noise caused by high frequency distortion in the modulation stage of the modulated signal. It is an object of the present invention to provide a modulator that can improve conversion gain as well.

FIG. 1 shows a specific circuit of an example of a conventional modulator. In the figure, a pair of NPN transistors Q ₁ and Q ₂ have their emitters connected in common, and their emitters are connected to the collector of a constant current NPN transistor Q ₃ . Also, transistors Q ₁ , Q ₂
The bases of each are connected to the emitter and collector of the NPN transistor _Q4 via coupling capacitors _C1 and _C2 . Furthermore, transistors Q ₁ , Q ₂
A variable resistor VR ₁ is connected between the bases of the variable resistor VR 1, and its slider is connected to the power supply terminal. In addition, R ₁ and R ₂ are the base bias resistance of transistor Q ₃ , R ₃ and R ₄ are the collector load resistance of transistors Q ₁ and Q ₂ , and R ₆ and R ₇ are the collector load resistance and emitter resistance of transistor Q ₄ . and also a bypass capacitor to the emitter resistor _R5 of transistor _Q3
C ₄ is connected.

In the conventional modulator having the above configuration, a modulation signal is supplied from the input terminal 1 to the base of the transistor Q ₃ via the capacitor C ₃ , and a carrier wave is supplied from the input terminal 2 to the base of the transistor Q ₄ .
The carrier wave from input terminal 2 is taken out from the emitter of transistor Q ₄ in the same phase and applied to the base of transistor Q ₁ through capacitor C ₁ , while it is taken out from the collector of transistor Q ₄ in opposite phase and applied to the base of transistor Q 1 through capacitor C ₂ . _Q2
applied to the base of As a result, transistors Q ₁ and Q ₂ are alternately turned on and off, and the carrier wave is balanced-modulated from the collector of transistor Q ₂ to output terminal 3 by the modulation signal from input terminal 1, and the carrier wave component is suppressed. A modulated wave is output. Note that the variable resistor VR ₁ performs adjustment to create a completely balanced state. Such a modulator (balanced modulator) is used for frequency conversion of an audio signal in a television signal to a broadcast band, for example, and for various other purposes.

However, in the conventional modulator mentioned above, the carrier wave is
There is no problem if the frequency is around the VHF band, but
At high frequencies such as the UHF band, transistors
It was difficult to obtain two signals that were in an antiphase relationship with each other due to the distributed capacitance of the collector and emitter of _Q4 . The same is true when using a transformer to create two signals that are in antiphase with each other.
When inputting a high-frequency carrier wave such as the UHF band, the distributed capacitance of the transformer secondary coil causes the respective phases to shift and become unbalanced, making it impossible to put it to practical use.
Furthermore, conventional modulators have the disadvantage of generating high frequency distortion when a large modulation signal is input.

The present invention eliminates the above-mentioned drawbacks and also increases the conversion gain, as shown in Figures 2 and 3 below.
One embodiment will be described with reference to the drawings.

FIG. 2 shows a specific circuit of one embodiment of the modulator according to the present invention. In the figure, the emitters of a pair of NPN transistors Q ₅ and Q ₆ are connected in common and further connected to the collector of a constant current NPN transistor Q ₇ . For T ₁ , the primary coil is input terminal 4,
4', and the center tap of the secondary coil is grounded, and the input terminals 4, 4'
Two signals are created, one in phase and the other in phase with the input signal. One end of the secondary coil of the transformer T ₁ is connected to the base of the transistor Q ₄ via a capacitor C ₅ and a resistor R ₈ in series, and the other end of the secondary coil is connected to a capacitor C ₆ and a resistor R ₉ , respectively. Connected in series to the base of transistor _Q6 . In addition, the bases of transistors Q ₅ and Q ₆ are connected to capacitors C ₈ and
C is grounded through ₉ . Therefore, a low-pass filter is formed by resistor R ₈ and capacitor C ₈ ,
A low pass filter is formed by resistor R ₉ and capacitor C ₉ .

Also, the connection point of resistor R ₈ and capacitor C ₈ and the resistor
A variable resistor VR ₂ is connected between R ₉ and the connection point of _the capacitor C ₉ ;
The slider of is connected to the power supply terminal while being grounded via capacitor _C7 . This variable resistor
VR ₂ is for adjusting the bias of transistors Q ₅ and Q ₆ to make their characteristics the same.

Furthermore, the collector of transistor Q ₅ is connected to one end of the primary coil of transformer T ₂ via coil L ₁ , while the collector of transistor Q ₆ is connected to one end of the primary coil of transformer T ₂ via coil L ₂ . connected to the other end. The center tap of the primary coil of the transformer _T2 is connected to the power supply terminal via an integrating circuit consisting of a capacitor _C10 and a resistor _R10 .
Coils L ₁ and L ₂ are air-core coils for correcting variations in impedance of both windings on the primary side of transformer T ₂ , and together with transformer T ₂ , leakage of carrier wave components to output terminal 6 when no modulation is performed. prevent. The secondary coil of the transformer T ₂ is connected to the output terminal 6.

Furthermore, the emitter of transistor _Q7 is a resistor.
R ₁₂ and a bypass capacitor C ₁₂ are grounded via a parallel circuit, while the base of the transistor Q ₇ is connected to the input terminal 5 via a capacitor C ₁₁ . Resistor _R11 is a base bias resistor for _Q7 .

In this embodiment, two signals with opposite phases generated using the transformer _T1 are shifted from each other when the frequency is high as described above, so in order to avoid this phenomenon, a carrier wave whose frequency is much higher than that of the modulation signal is used. is injected from the base of the transistor Q ₇ , and the modulation signal is applied to the transformer T ₁ from the input terminals 4 and 4', thereby injecting the modulation signals having opposite phases to each other into the bases of the transistors Q ₅ and Q ₆ . Here, the collector currents I _{c5 and} I _c6 of transistors Q 5 and _{Q 6} are caused by the diodes between the base and emitter of transistors Q ₅ and Q ₆ , and the emitter currents of Q ₅ and Q ₆ are I _s5 exp
(qV _BE5 /kT), I _s6 exp (qV _BE6 /kT), so the collector currents I _{c5 and} I _c6 , which are approximately equal to this emitter current, can also be approximately expressed as I _c5 I _s5 exp (qV _BE5 / kT). kT) (1) I _c6 I _s6 exp (qV _BE6 /kT) (2) It can be expressed by the general formula: However, in formulas (1) and (2), I _s5 ,
I _s6 is the saturation current value of Q ₅ and Q ₆ when reverse bias voltage is applied, V _BE5 and V _BE6 are the base-emitter voltage values of Q ₅ and Q ₆ , q is the electron charge, T is the absolute temperature, and k indicates Boltzmann's constant.

Since the modulation signal e _x that enters the input terminals 4 and 4' is of low frequency, it is converted into two modulation signals with accurate anti-phase relation to each other by the transformer _T1 , and one is connected to the resistor _R8 through the coupling capacitor _C5 . and capacitor C ₈ and are fed to a low-pass filter consisting of
Here, after the high frequency component is removed, the transistor
The other modulation signal is fed to the base of Q ₅ and is fed through a coupling capacitor C ₆ to a low-pass filter consisting of a resistor R ₉ and a capacitor C ₉ , where high frequency components are removed and then the other modulated signal is passed to the base of transistor Q ₆ .
supplied to the base of Further, the carrier wave e _y that has entered the input terminal 5 is supplied through the capacitor C ₁₁ to the base of the transistor Q ₇ that operates at a constant current, thereby causing it to switch.

As a result, if the modulation signal e _x and the carrier wave e _y are respectively expressed as e _x = E _s cosω _s t e _y = E _c cosω _c t (3) for simplicity of explanation, then the transistors Q ₅ and Q ₆ The signal e ₀ taken out from the collector of , passed through the transformer T ₂ and output from the output terminal 6 is expressed by the following equation using equations (1) and (2).

e ₀ =A・e _x・e _y =1/2AE _c・E _s {cos(ω _c +ω _s )t+
cos(ω _c −ω _s )t}=F(ω _c ±ω _s ) (4) Therefore, the output signal e ₀ is ω _c +ω _s obtained by balanced modulating the carrier wave e _y with the modulation signal e _x A _{modulated wave} having two angular _frequency components of . The variable resistor VR ₂ is an adjustment variable resistor for achieving the above-mentioned balanced state.

Furthermore, in order to suppress the carrier wave component in the output modulated wave, it is sufficient to input a large modulation signal e _x and create a level difference between it and the carrier wave e _y . However, as a side effect, the static characteristics of the transistors Q ₅ and Q ₆ are particularly affected by the nonlinear part of _the static characteristics.
If the base input high frequency component of Q ₆ is at a large level, harmonic distortion will occur in the output modulated wave signal. However, in this embodiment, the high frequency components are limited by the low-pass filter made up of _R8 and _C8 and the low-pass filter made up of _R9 and _C9 , so the harmonic distortion can be reduced.

Furthermore, the above capacitors C ₈ and C ₉ are transistors.
Since the bases of Q ₅ and Q ₆ are grounded at high frequency,
In particular, since it works to pass high frequency carrier waves, the gain of transistors Q ₅ and Q ₆ can be increased.
Conversion gain becomes large. This gives the carrier component f _c
and the sideband component f _c ±f _s can be made large.

From the above, the frequency spectrum of the output signal of the output terminal 6 according to this embodiment is as shown in FIG. 3, and the signal level of the carrier frequency f _c is higher than the primary sideband level of f _c ±f _s as shown in It is sufficiently suppressed, and the levels of harmonics f _c +2f _s and f _c +3f _s shown also are sufficiently reduced. Note that f _s is the modulation signal frequency.

In addition, when using an FM or AM audio signal with a carrier frequency of 6.5 MHz as a modulation signal, or a signal in the UHF band (for example, around 600 MHz) as a carrier wave, the RF audio output of the SECAM television signal is However, it goes without saying that the present invention is not limited to such uses. It is clear that field effect transistors may be used instead of bipolar transistors for _Q5 to _Q7 , and transistors may be used as the phase dividing means.

As described above, the modulator according to the present invention includes a pair of first and second transistors whose emitters are commonly connected, and a pair of first and second transistors whose emitters are commonly connected to each other, and a second transistor whose collectors are commonly connected to the respective emitters of the first and second transistors. a first modulation signal output terminal of the phase division means and a base of the first transistor; a first low-pass filter including a first capacitor connected between the base of the first transistor and ground; a second modulation signal output terminal of the phase splitting means; a second low-pass filter connected between the base of the transistor and a second capacitor connected between the base of the second transistor and ground; Since the modulated wave is output by modulating the carrier wave supplied to the base of the system, it is possible to obtain a modulated wave in which the carrier wave component is sufficiently suppressed, even when the carrier wave frequency is high (e.g. UHF band). Furthermore, since the high frequency components of the modulated signal are attenuated by the first and second low-pass filters, even if the modulated signal level is high, harmonic distortion components generated in the modulated wave based on the high frequency components are suppressed. Further, the first and second low-pass filters include first and second capacitors connected between the bases of the first and second transistors and ground, and the first and second low-pass filters are configured to include first and second capacitors connected between the bases of the first and second transistors and ground. Since the second capacitor serves to pass particularly high-frequency carrier waves, the first and second transistors can be operated with their bases common, and the gain of these transistors can be increased, resulting in conversion. It has many features such as being able to increase the gain and thereby making it possible to sufficiently increase the difference between the carrier wave component and the primary sideband component in the resulting modulated wave.

[Brief explanation of the drawing]

Fig. 1 is a specific circuit diagram showing an example of a conventional modulator, Fig. 2 is a specific circuit diagram showing an embodiment of the modulator according to the present invention, and Fig. 3 is the modulated wave output of Fig. 2. FIG. 1, 4, 4'...Modulation signal input terminal, 2, 5...
...carrier input terminal, 3,6...output terminal, Q ₁ ~
Q ₇ ... NPN transistor, T ₁ , T ₂ ... Transformer, L ₁ , L ₂ ... Coil, R ₈ , R ₉ ... Resistor for low-pass filter, C ₈ , C ₉ ... Capacitor for low-pass filter .

Claims (1)

[Claims] 1. A pair of first emitters connected in common.
and a second transistor, a third transistor whose collectors are commonly connected to respective emitters of the first and second transistors, and a third transistor whose collectors are commonly connected to the respective emitters of the first and second transistors;
a phase dividing means for phase-dividing the modulated signal into a modulated signal; connected between the first modulating signal output terminal of the phase dividing means and the base of the first transistor;
and a first low-pass filter including a first capacitor connected between the base of the first transistor and ground; and a first low-pass filter including a first capacitor connected between the base of the first transistor and ground; connected between the base and
and a second low-pass filter including a second capacitor connected between the base of the second transistor and ground, and modulating the carrier wave supplied to the base of the third transistor with the modulation signal. A modulator characterized by outputting a modulated wave.