JPH0351124B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an integrated FM modulator.

Low-voltage operating circuits are necessary for high integration of ICs. However, conventional FM modulators have had the problem of requiring a relatively high power supply voltage. Below, the above-mentioned problems will be explained in detail using the drawings.

First, the necessity of a low voltage operation circuit is as follows. That is, the size of an element within an IC is related to its breakdown voltage; in other words, the higher the breakdown voltage is, the higher the operating voltage is, the larger the element area becomes, resulting in an increase in chip size and poor yield. Therefore, it is necessary to enable low-voltage operation and to miniaturize the elements within the IC.

Next, a conventional FM modulator will be described. 1st
The figure shows a block diagram of a conventional FM modulator. In the figure, 1 is an unstable multivibrator,
The oscillation frequency is compared with the collector current value of the voltage-current conversion transistor 2. 5
is a resistor, and 4 is an input terminal for a modulation signal.

Here, we will consider an FM modulator for a home VTR, and the modulation signal will be a video signal. The video signal input to the input terminal 4 is a signal in which the leading edge of the synchronizing signal is clamped to a constant DC potential, the high frequency component is emphasized by pre-emphasis, and the white and black side levels are further clipped.

Now, as shown in Figure 2, let ν _{1 (peak-to-peak value) be from the top of the synchronizing signal of the video signal at input terminal 4 to the 100% white level, and let the white and black clip levels (WL and BL, respectively) be ν 1} (peak-to-peak value). Let a% and b%. However, in this case, 100% is from the sync signal tip to the 100% white level, and each clip level is measured from the sync signal tip.

Under the above conditions, if the DC potential at the tip of the synchronization signal is Es, the peak potential of the signal at the input terminal 4 is Es+a/100ν _{1 .} . . Equation (1). Also, the lowest potential of the signal at the emitter of transistor 2 is Es-b/100ν ₁ -V _BE . . . Equation (2) where V _BE is the voltage between the base and emitter of the transistor. Considering the temperature characteristics and voltage-current conversion linearity of the FM modulator, the lowest potential of the signal at the emitter of transistor 2 needs to be ν ₁ or more. Therefore, Es−b/100ν1−V _BE >ν ₁ ...Equation (3). In this case, the peak potential of the signal at the input terminal 4 is equal to or higher than {(1+a+b/100)ν ₁ +V _BE ).

In other words, the input section of the unstable multivibrator requires a dynamic range of {(1+a+b/100)v ₁ +V _BE } or more. Therefore, the FM modulator requires a power supply voltage equal to this value plus the operating voltage of the unstable multivibrator 1.

Figure 3 shows an example of an astable multivibrator circuit often used in integrated FM modulators. In the figure, 10 is a diode, 11, 12, 19, 2
0, 24, and 25 are resistors, 13 to 18 are transistors, 21 is a capacitor, and 26 is a constant voltage source.
Furthermore, in the figure, elements having the same reference numerals as in FIG. 1 have the same functions. Note that since the operation of this circuit is well known, its explanation will be omitted.

FIG. 4A shows the emitter voltage waveform of transistor 17, and FIG. 4B shows the base voltage waveform of transistor 222. The power supply voltage is Vc.c., constant voltage source 26
When the potential of the transistor 17 is V _A and the voltage between the base and emitter of the transistor is V _BE , the lowest emitter potential of the transistor 17 is (V _A −3V _BE ). If the peak-to-peak value of the signal applied to the base of transistor 22 is ν ₂ , the lowest potential at the emitter of transistor 22 is at most (V _A −3V _BE )−ν ₂ −V _BE =V _A −ν ₂ −4V _BE ...Equation (4) is obtained. Therefore, the operating voltage of the unstable multivibrator is Vc.c.−(V _A −ν ₂ −4V _BE )=(Vc.c.−V _A ) +ν ₂ +4V _BE ……Equation (5) .

Next, as an example, by substituting various practical values into the above equation and calculating the operating voltage of the unstable multivibrator and the dynamic range of the input section, the following results are obtained.

(Vc.c.−V _A ) is given by the waveform shown in Figure 4A.
Approximately 0.5V is required, and ν ₂ is transistor 2
From the switch switching characteristics of 2 and 23, about 0.5V, ν ₁
is about 0.5V. Also, based on the VHS standard for home VTRs, a = 160, b = 40, and V _BE = 0.7.
Then, the operating voltage of the astable multivibrator is 3.8V, and the dynamic range of the input section is 2.2V. Therefore, the dynamic range of the input section accounts for 37%, which is quite high.

In the future, if the clip level can be increased as the frequency characteristics of tape head systems improve,
Since a wider dynamic range is required in the input section, it becomes increasingly difficult to lower the voltage.

An object of the present invention is to eliminate the drawbacks of the prior art described above and to provide an integrated FM modulator capable of low voltage operation.

In order to achieve the above object, the present invention provides PNP
A voltage-to-current conversion circuit is constructed using a transistor and a constant current source, and the AC voltage dynamic range at the input section of the unstable multivibrator is eliminated, making it possible to lower the power supply voltage of the RM modulator. There is.

FIG. 5 shows a schematic circuit diagram of an embodiment of the present invention. In the figure, 5 and 8 are resistors, 6 is a PNP transistor, 7 is an NPN transistor, and 9 is a constant voltage source. Further, in this figure, parts with the same symbols as in FIG. 1 have the same functions.

The synchronization signal tip potential at input terminal 4 is Es,
Let the AC signal from the tip of the synchronization signal be ein, the resistance value of the resistor ₅ be R5, and the power supply voltage Vc.c. at this time
If _hFE is ignored, the collector current of the PNP transistor 6 can be expressed as Vc.c.-(Es+ein+ _VBE )/ _R5 ...Equation (6).

Further, if the potential of the constant voltage source 9 is E ₁ and the resistance value of the resistor 8 is R ₅ , and h _FE is similarly ignored, the collector current of the transistor 7 is E ₁ −V _BE /R ₈ . . . Equation ( 7) becomes. Therefore, astable multivibrator 1
The current flowing from I= _E1 − _VBE / _R8 −Vc.c.−Es− _VBE / _R5 +ein/ _R5 can be expressed as Equation (8).

That is, since this current is proportional to the signal at the input terminal 4, the circuit of FIG. 5 constitutes an FM modulator, similar to the conventional circuit shown in FIG.
The lowest potential _einL of the input signal ein is expressed by the following equation (9): einL=-b/100v ₁ under the same conditions as in the conventional example. Therefore, =E ₁ −V _BE /R ₈ −Vc.c.−Es−V _BE /R ₅ +1/R ₅・(
-b/100v ₁ A)>0...It is necessary to select the constants of each circuit element and the potential of each part so that the equation (10) is satisfied. This can be easily achieved by reducing the resistance value _R8 of the resistor 8.

Since the transistor 7 is a constant current source, its base potential _E1 should normally be selected to be about 1V. Therefore, the power supply/voltage of the FM modulator may be the sum of the above 1V and the operating voltage of the astable multivibrator, 3.8V. Therefore, the power supply voltage is approximately
Can be lowered by 1.2V. The reason for this will be explained below.

1 in FIG. 5, which is an embodiment of the present invention, is the same as the unstable multivibrator 1 in FIG. 1, as described above, and its specific circuit is shown in FIG. elements 2, 3, 4
other circuits). Therefore, to explain the combination of the non-stable multivibrator of FIG. 3 and the circuit of the present invention shown in FIG. 5, the collector potential of the transistor 7 is determined by the base potential of the transistor 22 or 23 constituting the non-stable multivibrator. . This is because transistor 6 and transistor 7 operate as current sources, so the impedance on the collector side of transistor 6 and transistor 7 seen from the collector node of transistor 7 is extremely high. Usually, it is several hundred kΩ. On the other hand, although the transistors 22 and 23 operate as switches, the transistor that is turned on operates as an emitter follower, so its impedance is extremely low. Usually, it is several tens of ohms. Therefore, the potential at the node is the same as in the conventional example, and its value is as expressed by the above equation (4). In this case, the input dynamic range of the PNP transistor 6 can be taken up to the operating voltage of the unstable multivibrator 1 of 3.8V, so there is no problem even if the clip level is increased.

As is clear from the above description, according to the present invention, a dynamic range as an AC voltage is not required at the input section of the unstable multivibrator that constitutes the FM modulator, and the power supply voltage can be lowered by about 1.2V. . Therefore, it is possible to lower the breakdown voltage of the element within the IC and reduce the element area, making it easy to reduce the chip size and improve yield. On the other hand, if the chip sizes are made equal, the degree of integration can be further increased. Furthermore, since the dynamic range of the video signal input section is widened, if it becomes possible to raise the clip level by improving the frequency characteristics of the tape head system, the effects of the present invention will become even more remarkable.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional FM modulator, Figure 2 is a block diagram of a conventional FM modulator.
3 is a circuit diagram of a conventional FM modulator, FIG. 4 is an operating waveform diagram of the FM modulator, and FIG. 5 is a waveform diagram for explaining the input signal of the FM modulator. FIG. 2 is a block diagram of an embodiment. 1... Unstable multivibrator, 6...
PNP transistor, 9...constant voltage source.

Claims (1)

[Claims] 1. An unstable multivibrator whose oscillation frequency is proportional to the emitter current of a transistor to which a DC voltage is applied to the base, a PNP transistor to which an input signal is supplied to the base, and a constant current source connected to the collector of the PNP transistor. An integrated FM modulator, characterized in that the collector of the PNP transistor and the emitter of the transistor of the astable multivibrator are connected.