JPS5922492A - Integrated fm modulator - Google Patents

Abstract

PURPOSE:To attain the low voltage operation and to set an oscillating frequency with high accuracy and simple constitution, by eliminating an AC voltage dynamic range at an input section of an astable multivibrator and bringing a power supply voltage of an FM modulator to a low voltage. CONSTITUTION:A circuit surrounded with broken lines 9 is a bias circuit giving a base voltage of a PNP transistor(TR) 37 and a voltage of the emitter of the TR37, i.e., a voltage of an IC external terminal 58 is eliminated for the temperature characteristic by selecting suitably the value of resistors 50-53. Further, a circuit surrounded with broken lines 8 is a bias circuit giving a base voltage of an NPNTR38 and a voltage of the emitter of the TR38, i.e., the voltage of the IC external terminal 60 is eliminated for the temperature characteristic by selecting suitably the values of resistors 45-48. An oscillating frequency corresponding to a DC level at the tip of synchronizing part and 100% white level is adjusted with an externally mounted resistor 56, and the DC level at the tip of the synchronizing part is adjusted to a prescribed oscillating frequency with externally mounted resistors 55, 57.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an FM modulator suitable for integration.

Conventional FM modulators have the drawback of requiring a relatively high power supply voltage and are not suitable for low power consumption or high integration of ICs. In other words, power consumption increases with a high power supply voltage, and the higher the operating voltage and higher withstand voltage of the IC elements, the larger the element area becomes, leading to an increase in chip size and a decrease in yield. Ta.

FIG. 1 shows a block diagram of a conventional FM modulator. In FIG. 1, 1 is an unstable multivibrator whose oscillation frequency is proportional to the collector current value of the voltage-current conversion transistor 2. In FIG. 6 is resistance, 4
is the input terminal for the 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 Fig. 2, the period from the top of the synchronization signal of the video signal at the input terminal 4 to the 100% white level is defined as vl (peak-to-peak value), and the white and black clip levels (WL and BL, respectively) are expressed as α coefficients. .

h%. However, in this case, the tip of the synchronization signal is 10
It is assumed that the level is 100% up to the 0% white level, and each clip level is measured from the tip of the synchronization signal.

Under the above conditions, the DC potential at the tip of the synchronization signal is
Then, the peak potential of the signal at the input terminal 4 is ES+'''J00.The lowest potential of the signal at the emitter of the transistor 2 is, where: Vsg+'f, the emitter-to-emitter voltage of the transistor. Considering the temperature characteristics and voltage-current conversion linearity of the pH modulator, the lowest potential of the signal at the emitter of transistor 2 must be v1 or more. It is necessary to clamp the input of the stable multivibrator.Therefore, at this value, the unstable multivibrator 1
The operating voltage of Take(r) plus the power supply voltage is l? It is necessary as an M modulator.

Next, FIG. 3 shows a specific circuit example of a conventional integrated FM modulator. In Figure 3, 1o is a diode, N, 12
, 19, 20, 21j22 are integrated resistors 1.13-18
, 25, 24, 2 are integrated transistors, 25 is a constant voltage source, 26 is an integrated range, 27 to 29 are external resistors,
5, 3G is an external adjustment resistor, 31 is an external capacitor, 32 to 54
is an IC external terminal, and 35 is a power supply line.

Further, in FIG. 6, elements having the same symbols as those in FIG. 1 have the same functions. Incidentally, since the operation of this circuit is well known, the explanation thereof will be omitted, but 10 to 51 constitute the unstable multivibrator 1.

Here, FIG. 4) shows the emitter voltage waveform of the transistor 17, and V3) of the same figure shows the base voltage waveform of the transistor 260. Vcc is the power supply voltage, VA is the potential of the constant voltage source 26, VsI is the voltage between the base and the capacitor of the Lasis resistor.
c, the lowest emitter potential of transistor 17 is (
VA-5Vag). If the peak-to-peak value of the signal applied to the base of the transistor 230 is v2, the lowest emitter potential of the transistor 25 is at most (VA-5Vsg) -v2-Vsg = VA-v
It becomes 2-4 Ins. Therefore, the operating voltage of the unstable multivibrator is Vcc - (VA-υ2-4 VBg') = (V
cc-VA)+ν2+4VBE.

Next, as an example, by substituting various practical values into the above equation and calculating the operating voltage and dynamic range of the input section of the unstable multi-by-break, the result is as follows.

(Vcc V, t) is required to be about 0.5 V according to the waveform shown in Fig. 4), and s v2 is the voltage of transistor 2.
5.

From the switch switching characteristics of 24, about 0.5V, ν1 is 0
．． It is about 5. Also, based on the VH5 standard for home VTR, d=160. A=40 and Vrtg=0.
7, the operating voltage of the unstable multivibrator is 3
．． 8V, and the dynamic range of the input section is 2.2V. Therefore, the ratio occupied by the dynamic range of the input section is 37%, which is quite high, making it unsuitable for low voltage driving.

In the future, if the clip level becomes higher as the frequency characteristics of tape head systems improve, a wider dynamic range will be required at the input section, making it increasingly difficult to reduce the voltage.

By the way, the oscillation frequency f of the astable multivibrator 1 is such that 31 is Co and the current flowing through the resistor 6 is I.

Then, it can be approximately expressed by the following equation.

1°f" 4 Co (Vcc - VA) Therefore, the oscillation frequency f fluctuates due to variations in the integrated resistor that determines the capacitance C'o and VA. Therefore, a predetermined oscillation frequency is set corresponding to each potential of the clamped video signal. In order to obtain the DC level and 100%
The oscillation frequency difference corresponding to the white level is adjusted, and the resistor 5
0 adjusts the DC level at the tip of the synchronizer to a predetermined oscillation frequency. That is, the resistor 3 is changed to adjust the current and amount of change corresponding to the input video signal 4. Furthermore, the oscillation frequency is adjusted by changing the resistor 5o and changing the current discharged through the resistor 28t29.

However, while the voltage at the IC external terminal 54 H52 depends on the VBE K of the nine integrated transistors as shown in FIG. 4, the adjustment circuit consisting of 27 to 5o is an external circuit, and Since it is difficult to match the temperature characteristics, the oscillation frequency tends to fluctuate with temperature.

Furthermore, as shown in Fig. 3, the IC external terminals 32 and 54, where high-frequency FM signals are generated, require many external adjustment parts, which increases costs and tends to cause blacktalk to other peripheral circuits. was there.

SUMMARY OF THE INVENTION An object of the present invention is to provide an integrated FM modulator that eliminates the drawbacks of the prior art described above, is capable of low voltage operation, and is capable of setting the oscillation frequency with high precision with a simple configuration.

In order to achieve the above object, the present invention inputs a voltage signal to the emitter of a common base transistor through a resistor, and also connects the collector of the transistor, which together with the resistor constitutes a constant current source, and the common base transistor. The collector is connected to the astable multivibrator input section to eliminate the AC voltage dynamic range at the astable multivibrator input section and to enable a low power supply voltage for the FM modulator. Furthermore, external resistors are connected to the emitters of each of the six transistors, making it possible to adjust the oscillation frequency.

Hereinafter, one embodiment of the present invention will be explained with reference to FIG. Fifth
In the figure, 36 is an integrated capacitor, 57 is a PNP transistor, 3B, 41.44 is an NPN transistor, 39, 40.45 is an NPN diode, and 42 is a PNP transistor.
NP diode, 45 to 53 are integrated resistors, 54 is a constant current source, 55, 56, 57 are external adjustment resistors, 58 to 60 are IC external terminals, and those with the same functions as in Fig. 3 have the same symbols. It is attached.

Next, the operation shown in FIG. 5 will be explained. The input signal 4 is outputted from an IC external terminal 59 to the outside of the IC via a transistor 44 and a constant current source 54 forming an Emifluoro.

Note that the transistor 440 base-emitter voltage Vsg
The input signal is set to 01% to compensate for the temperature characteristics of the IC.
The external terminal 59 is kept free from temperature fluctuations.

Break #! The circuit surrounded by 9 is a PIVP transistor 57
This is a bias circuit that provides a base voltage of 50~
By appropriately selecting the value of 53, the voltage at the emitter of the PNP transistor 37, that is, the IC external terminal 58, is made to have no temperature characteristics.

The circuit surrounded by a8 is the NPN transistor 58.
This is a bias circuit that provides a base voltage of
By appropriately selecting the value of 48, the voltage at the emitter of the NPIV transistor 58, that is, the IC external terminal 60, is made to have no temperature characteristics.

The signal at the IC external terminal 59 is connected to the external resistor 56'! 7, a PNP transistor 57 used with a common base
The current signal is input to the neimitter of the transistor 67, and becomes the collector current signal of the transistor 67. Also, since the NPIV transistor 58 and the external resistor 57 constitute a constant current source, the collector of the transistor 37 and the current signal are input to the unstable multi-by-break 1, and the whole constitutes an FM modulator. ing.

Therefore, the external resistor 56 can adjust the DC level at the tip of the synchronizing section and the oscillation frequency corresponding to the 100% white level, and the external resistors 55 and 57 can adjust the DC level at the tip of the synchronizing section and the oscillation frequency corresponding to the 100% white level.
The C level can be adjusted to a predetermined oscillation frequency with fewer external components than before.

The oscillation frequency can be obtained. Also, IC external terminal 58
, 59, and 60 do not have temperature characteristics, so the oscillation frequency does not vary with temperature.

However, in order to improve ease of use, VTRs and the like are required to be smaller and lighter. Therefore, by forming and integrating the resistor as a thick film resistor on a ceramic substrate and increasing the resistance value by applying a laser to the thick film resistor and scratching the thick film resistor, the resistance value can be adjusted quickly and automatically. Laser trimming technology is widely used as an essential technology.

According to the present invention, when adjusting the oscillation frequency using the laser trimming technique described above, by trimming the resistors 55° and 57 (resistance value increases), the oscillation frequency increases in the former case and decreases in the latter. There is an advantage that 55 and 57 can be set to optimal values from the beginning, and the adjustment time can be shortened. Furthermore, if the value of one of the resistors is made too large in the trimming adjustment of the resistors 55 and 57, the value of the other resistor can be increased by trimming, and highly accurate adjustment is easily possible.

By the way, since the transistor 38 is a constant current source, its base potential VB should normally be selected to be about 1V. Therefore, the power supply voltage 55 of the FM modulator may be a value obtained by adding the operating voltage of the unstable multipipe rake 1 of 6.8 V to the above-mentioned 1 V, which is about 1.2 V lower than the conventional voltage.

In other words, according to the present invention, the input section of the unstable multivibrator that constitutes the FM modulator does not require a dynamic range as an AC voltage signal.
It can be lowered by about V. Therefore, it is possible to lower the withstand 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.

Further, according to the present invention, it is no longer necessary to use both ends of the capacitor 56 as IC external terminals for the above-mentioned adjustment, and it becomes possible to integrate the capacitor 56 as shown in FIG. 5, reducing the number of IC external terminals to 2. Not only can you reduce the number of items, but you can also get the following effects.

When the capacitor is used as a peripheral component, the external terminal of the IC has a different stray capacitance value due to the relationship with adjacent bins, so in order to reduce this influence, the capacitance value C needs to be several tens of PF. The current 1o in that case, i.e. 4c (VCc
-VA) f has a value several times larger than that in the case of integration.

On the other hand, in the case of a built-in capacitor, there is no need for an external terminal, so there is no need to consider the unbalance of the stray capacitance of the bottle, and the capacitance can be reduced -c, @7). -Keoi,
. =,. . If P''P, * is set to ' == 1o PF, I'o / Io = 0.25, the current consumption can be reduced to 7, and power consumption can be reduced.

There is also the advantage that high frequency components do not leak to the outside of the IC, and crosstalk to others can be eliminated.

Further, FIG. 6 shows another embodiment of the present invention. % in Figure 6
61, 62 and 65 are external adjustment resistors, and those having the same functions as those in FIG. 5 are given the same numbers. In FIG. 6, a voltage signal outputted from inside the IC to an external IC terminal 59 is input to the emitter of an N'PN transistor 58 whose base is grounded via a resistor 61, and the collector current signal of the transistor 38 is inputted to the emitter of an N'PN transistor 58 whose base is grounded. will be exchanged.

On the other hand, since the PNP transistor 37 and the external resistor 62 constitute a constant current source, the collector and current signals mentioned above are input to the unstable multivibrator 1. Further, the oscillation frequency difference between the DC level at the tip of the synchronization section and the 100% white level can be adjusted with a resistor 61, and the oscillation frequency can be adjusted with resistors 62 and 65. Therefore, the fifth
It is clear that the same effect as in the case of the circuit example shown in the figure can be obtained. Furthermore, compared to the circuit example shown in Fig. 5, in the circuit shown in Fig. 6, the common base transistor through which the collector current signal passes is constructed of an NPN transistor with good frequency characteristics. It has the advantage of being able to perform FM modulation.

As described above, according to the present invention, the power supply voltage can be lowered, power consumption can be reduced, the size of the IC chip can be reduced, and a highly accurate FM modulator can be realized with a small number of peripheral components.

[Brief explanation of drawings]

Figure 1 is a block diagram of a conventional FM modulator, and Figure 2 is a block diagram of a conventional FM modulator.
A waveform diagram explaining the input signal of the modulator, Fig. 6 is the conventional F
A circuit diagram of an M modulator, FIG. 4 is an operating waveform diagram of a conventional FM modulator, FIG. 5 is a circuit diagram showing one embodiment of the present invention, and FIG. 6 is a circuit diagram showing another embodiment of the present invention. It is a diagram. 1... Unstable multivibrator, 4... Input terminal signal, 5, 50, 56957, 61, 62... External adjustment resistor, 36... Integrated capacitor, 57... PNP) transistor , 38...NPN transistor. tllIffl f2 Hio Togo

Claims (1)

[Claims] a first transistor whose base is grounded in alternating current; a second transistor whose conductivity type is inverse to that of the first transistor whose base is grounded in alternating current; and an unstable multivibrator; An integrated circuit characterized in that a signal is input to the emitter of the second transistor via a resistor, and the collector of the first transistor, the collector of the second transistor, and the input part of the unstable multivibrator are connected. FM modulator.