JPS5831126B2 - current controlled oscillator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a current controlled oscillator suitable for, for example, a PLL-MPX-IC.

Conventionally, in FM receivers, so-called PLL-MP
A stereo demodulator implemented as an integrated circuit called X-IC (multiplex integrated circuit using a phase-locked loop) is used.

FIG. 1 shows a conventional circuit used as a current (pressure) controlled oscillator for such a PLL-MPX-IC.

That is, a current (6) corresponding to the phase difference supplied through a low-pass filter (not shown) is passed through an integrating circuit 11 to drive the transistors Q1 to Q8 and the reschmitt circuit.

By the way, when incorporating such a circuit into a portable radio or the like and operating it at a low power supply voltage, the transistor Q
is, base-emitter voltage of Qa (VBB)
f-0,7V and Q4(7)-] 0.2V in collector-emitter saturation voltage (VOE(sat)), and Q1p
VBE of Q2==:=0.7V and VOE of Q7 (,a,
) -=0.2V, which is a total of 1.8V, is not suitable because it becomes an invalid voltage.

Note that this is the stabilization voltage vs tb and the minimum voltage used ■ cc
(min).

FIG. 2 shows the voltage relationship of the oscillation waveform seen from point A in the circuit in this circuit.

Therefore, this invention was made in view of the above points, and an object of the present invention is to provide an extremely good current controlled oscillator that can reduce reactive voltage as much as possible and operate with a low power supply voltage. There is.

An embodiment of the present invention will be described in detail below with reference to the drawings.

That is, as shown in FIG. 3, a control current (2) is generated in accordance with the phase difference via, for example, a low-pass filter (not shown).

Point B in the figure, where the current flows, is connected to the zero potential point O through the capacitor C8 and resistor R8 in parallel, which constitute the integrating circuit 21, and the base of one transistor Q1o of the input stage differential amplifier which constitutes the Schmitt circuit 22. Resistance R
1 to the collector of transistor Q14.

Here, the collector of one transistor Qio of the differential amplifier is connected to the zero potential point O via a current mirror circuit consisting of diodes Q12 and Q13, and the collector of the other transistor Qll is directly connected to the zero potential point O. The base thereof is connected to the zero potential point O via a resistor R3, to the collectors of the transistors Q and 5 via a resistor R2, and further to the stabilized negative power supply -Vstb via a resistor R4.

Further, the common emitters of the transistors Q14P and Q15 are connected to the stabilized negative power supply -Vstb, and the common bases thereof are connected to the collector of the transistor Q13 and the collector of the transistor Q1□.

The common emitters of transistors Q1o and Q11 of the differential amplifier are connected to the collector of transistor Q16.

Here, transistor Q16. Q17 has its common base connected to the bias power supply vB and the emitter of the former connected directly to the emitter of the latter connected to the negative power supply -VER through resistor R5.
connected to.

Note that the transistor Q13 of the current mirror circuit has its base connected to the collector of one transistor Q1o of the differential amplifier, and its emitter connected to the zero potential point O.

In such a configuration, the voltage relationship of the oscillation waveform seen from point B in the diagram is as shown in FIG.
The free-running oscillation frequency is determined by a time constant of 1, and the high potential -vH and low potential -vL are determined by the Schmitt circuit 22, and a current (
The oscillation frequency is controlled according to the PLL (in the case of PLL), but in explaining the detailed operating principle, point A in FIG. 4 is assumed to be the initial state.

At this time, point B in FIG. 3, that is, the base of transistor Q1o is at a potential of -VH, and transistor Ql
The base of l is also at -vH.

Here -■H2-■L is It is determined by

That is, in this case, the transistor QIQ of the differential amplifier
t Qll is in equilibrium and the collector current of its current source transistor Q16 is Qlo.

Half of the amount flows to Qll and half to each other.

The collector current of transistor Q1o has its direction reversed by diodes Q1□ and Q13 of the current mirror circuit, and is used to drive transistors Q14 and Q15.

Here, the collector current of the transistor Q1□ is set to be about half that of the transistor Q16, and when the transistors Q1o and Q1□ are in a substantially balanced state, the base current of the transistors Q14 p Q15 flows or not. becomes the limit state.

Until this point, transistor Qto was in the on state, so transistor Q14. Q1. Both continue to be in the on state, and the transistor Qll quickly returns to -vH.
However, the capacitor C8 of the integrating circuit 21 that determines the free-running oscillation frequency
The base of O has a period T2=C as shown in the 02 curve in Figure 4.
The potential shifts to a negative potential with a time constant of oR1, and when it reaches -vH, the transistors Q14 j Q15 are turned off.

And at this time, the base of transistor Qll quickly -
While the potential becomes vL, the base of the transistor Q1o gradually goes to zero potential with a time constant (period T1) of approximately CoRo as shown in the el curve in FIG. 4, and when it reaches -VI, the transistor Q14 + After Q15 is turned on, the same operation will be repeated.

By the way, in the above, the control current ■.

If there is, the oscillation frequency is changed, mainly affecting the T1 period in FIG. 4.

Now, if it is Ro) R1, the above-mentioned 61. e2 will be respectively, but if we set e1=-vL in equation (1) and (2)
By setting e2=-vH in the equation, the period T1. T2
It can be seen that .

FIG. 5 shows another embodiment, in which a transistor Q is connected to the base of the transistors Q and 4j Ql described above.
By adding too and making a Darlington connection with Ql4 s Ql5, the influence of the base current can be reduced.

Note that the diode QIOI is provided to prevent saturation of the transistor Q17.

Further, the variable resistor R1oo is provided so that a part of the timing resistor can be varied and the free running frequency can be controlled from the outside.

That is, in the current controlled oscillator of the present invention as described above, the reactive voltage is 2 of the transistor QIO.

E(sat) (-==: 0.2V) Similarly, VBE of transistor QIO+ QH (:o, 7v) and VOE of transistor Q16 (5at) (==o, 2V)
Total of 1. I V, which can reduce the VBE of one transistor (medium 0.7 V) compared to the conventional one, making it possible to use the lowest possible power supply voltage, and it can be fully put into practical use when incorporated into portable radios, etc. It is something.

Of course, if the power supply voltage is the same as that of the conventional one, the potentials of (1L) to (2)H can be increased, so that the stability can be improved accordingly.

In addition, since the integrating circuit 21 is based on the zero potential point O (a positive power supply is also possible), even when it is incorporated into a PLL-MPX-IC, it is possible to prevent the harmful effects of noise components from entering the IC. There are also benefits that can be prevented.

This is because if the reference potential point of the integrating circuit were to be the power supply VER shared with the lamp power supply of the stereo indicator, it would be easy to receive potential fluctuations of the power supply due to the large current on/off of the lamp, but as in this invention, This is because when a power source different from the lamp power source is used as a reference unit of the integrating circuit, such potential fluctuations do not occur.

Therefore, as described in detail above, according to the present invention, it is possible to provide an extremely good current controlled oscillator that can reduce the reactive voltage as much as possible and operate at a low power supply voltage.

In addition, in the above, the same operation can be achieved even if the NPN and PNP of the transistors used are replaced by simply changing the polarity of the power supply relationship, and the transistors Q16 and Q17 may be replaced with a constant current source such as a resistor, and furthermore, P
It is applicable not only to LL-MPX-IC but also to a so-called Disc-14 channel PLL demosimulator using subcarriers, and various modifications and applications are possible without departing from the gist of the present invention. Needless to say.

[Brief explanation of drawings]

1 and 2 are circuit diagrams showing a conventional current controlled oscillator and their oscillation waveforms, and FIGS. 3 and 4 are circuit diagrams showing an embodiment of the current controlled oscillator according to the present invention and their oscillation waveforms. figure,
FIG. 5 is a circuit diagram showing another embodiment. 21...Integrator circuit, 22...Schmitt circuit, Qlo-Ql7...Transistor, R
o-R5...Resistor, co...Capacitor, O...Zero potential point stb...Stabilized power supply, -■EF,... ...Negative power supply.

Claims (1)

[Claims] 1 between a CR integrating circuit having one end connected to a first potential point and the other end connected to a control current input terminal, and the first potential point and a second potential point lower or higher than the first potential point. first and second resistors connected in series; one base is connected to the control current input terminal, the other base is connected to the midpoint of connection between the first and second resistors; first and second transistors having a differential configuration, each having a collector connected to the first potential point via a current mirror circuit and the other collector directly connected to the first potential point; the respective emitters are commonly connected to the second potential point and the respective collectors are connected to respective bases of the first and second transistors via correspondingly third and fourth resistors; a first constant current connected between third and fourth transistors connected to each other, and a common emitter of the first and second transistors and a third potential point lower or higher than the second potential point; a second constant current source connected between a common base of the third and fourth transistors and the third potential point, the second constant current source being set to be approximately half the current from the first constant current source; A current controlled oscillator comprising a constant current source.