JPS6016093Y2 - Active filter oscillator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an active filter oscillator used in selective calling devices such as mobile radio equipment.

A device as described above includes a selective call squelch circuit.

Such a selective calling squelch circuit is generally used in a receiver, and in order to avoid hearing unnecessary communications when the same frequency is shared, the receiver is equipped with a circuit for selectively receiving tone signals.

In most cases, a filter having bandpass characteristics is usually used in a circuit that selectively receives tone signals.

It is desired that the filter described above allows only one particular tone signal to pass among a large number of tone signals, and provides sufficient attenuation to all other tone signals.

The selective calling device described above also includes a transmitter.

In the transmitter, the tone signal frequency selectively received by the aforementioned receiver is used as the modulation frequency.

In such devices, the filter is often switched between operating as a circuit for selectively receiving tone signals during reception and as a tuning element for an oscillation circuit at the same frequency as the tone signal during transmission. be.

In such a case, it is particularly required that the center frequency of the filter during reception and the oscillation frequency during transmission match.

In an oscillation circuit that uses a filter as a tuning element during transmission as described above, the oscillation must rise quickly.
No.

It is an object of the present invention to provide an active filter oscillator for use in devices such as those described above.

Another object of the present invention is to provide an active filter oscillator that reduces the rise time of oscillation during transmission for use in the above-mentioned device.

Yet another object of the present invention is to provide an active filter oscillator that can be manufactured as an integrated circuit.

The present invention will be explained below based on the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention.

In the figure, 1 to 3 are amplifiers, 4 to 6 are input terminals of amplifiers 1 to 3, respectively, 7 to 9 are output terminals of amplifiers 1 to 3, respectively, 10 to 12 are transistors, 13 to 25 are resistors, 26 to 27 is a capacitor, 28 is a signal input terminal, 2
9 is a signal output terminal, 30 is a control terminal, 31 is a voltage supply terminal, and 32 is a common ground terminal.

The resistor 13 is connected to the signal input terminal 28 and the input terminal 4 of the amplifier 1, the resistor 14 is connected to the input terminal 4 of the amplifier 1 and the output terminal 7, and the resistor 15 is connected to the output terminal 7 of the amplifier 1 and the input terminal 5 of the amplifier 2.
, the resistor 16 is connected between the output terminal 8 of the amplifier 2 and the input terminal 6 of the amplifier 3, and the resistor 18 is connected between the output terminal 9 of the amplifier 3 and the input terminal 6 of the amplifier 3.
are respectively connected to the input terminals 4 of.

Capacitor 26 is connected to input terminal 5 and output terminal 8 of amplifier 2.
One end of the capacitor 27 is connected to one end of the resistor 17, the other end of the capacitor 27 is connected to the input terminal 6 of the amplifier 3, and the other end of the resistor 17 is connected to the output terminal 9 of the amplifier 3. .

Furthermore, the output terminal 8 of the amplifier 2 is connected to a signal output terminal 29.

The circuit connection described above is the circuit 33 surrounded by the broken line in Figure 1.
It is expressed as.

A circuit 33 surrounded by a broken line shown in FIG. 1 is an RC active filter constructed by the state variable method.

In the figure, the resistance value of resistor 13718 is R□~
The capacitance values of R6 and capacitor 26.27 are C□
, C2, and assuming that the gain of the amplifier is sufficiently large, the transfer function T (S) of the above-mentioned filter is: , = Poryo abuse (2) and = Yingran Zhangjo tile
(3) 2R5 p (s) =SC2R4·R6/R, given by (4).

As can be seen from equation (1), the above-mentioned filter is a second-order band pass filter with a center angular frequency Wo and a sharpness Qo.

Also, from equations (1) to (4), the gain G at the center frequency of the filter.

is, G0 = to the flea (5) RIR6 It is expressed as

Normally, in the manufacture of active filters, in order to adjust the various characteristics of the filter to desired values, after the filter is completed, some of the passive elements of the filter are trimmed by an appropriate method, so that the various characteristics of the filter are adjusted to the desired values. A method is used to adjust the value.

In such a case, (2>, (3), <5'
Focusing on the formula, for example, first the center frequency of the filter is adjusted by changing R3 or R4, then the sharpness of the filter is adjusted by changing R6, and finally the gain of the filter is adjusted by changing R1. .

According to this method, the center frequency, sharpness, and gain, which are the main characteristics of the filter, can be adjusted independently by adjusting one passive element.

This is an essential advantage when manufacturing and adjusting active filters.

In the figure, amplifiers 1-3 can be operational amplifiers.

Operational amplifiers generally have a large gain (1 (lP ~ 1σ times)
, it has characteristics of high input impedance (several hundred kilohms) and low output impedance (several tens to hundreds of ohms).

The emitters of transistors 10 and 11 are coupled and their common point is grounded via resistor 19.

The base of the transistor 10 is connected to the output terminal 8 of the amplifier 2,
The collectors are respectively connected to voltage supply terminals 31.

The base of the transistor 11 is connected to a voltage supply terminal 31 via a resistor 21 and grounded via a resistor 22, and the collector is connected to the voltage supply terminal 31 via a resistor 20.

The base of the transistor 12 is connected to a voltage supply terminal 31 via a resistor 23 and to a control terminal 30 via a resistor 24.

The emitter of transistor 12 is connected to the collector of transistor 11, and the collector of transistor 12 is connected to resistor 2.
5 to the input terminal 4 of the amplifier 1.

The resistance values of the resistors 21 and 22 are set to values such that the DC voltage at the base of the transistor 11 is equal to the DC voltage at the output terminal 8 of the amplifier 2.

The base of the transistor 10 is connected to the output terminal 8 of the amplifier 2, and the DC voltages at the bases of the transistors 10, 11 are equal, and approximately the same DC current flows through the collectors of the transistors 10, 11.

Therefore, if the DC voltage at the base of the transistor 10.11 is VRg, and the DC voltage at the voltage supply terminal 31 is Vcc, and the resistance values of the resistors 19 and 20 are R7 and R8, then the DC voltage at the collector of the transistor 11 is V.

teeth V=Vcc 1. (VR-Vbe)R8 02R, (6) is given by

However, Vbe is the base-emitter forward voltage of the transistor.

The output signal of the amplifier 2 is applied to the base of the transistor 10, and as the signal voltage rises and falls, the collector and emitter of the transistor 10 become conductive and non-conductive, and the collector and emitter of the transistor 11 become non-conductive.・It is in a conductive state.

Therefore, when the collector and emitter of the transistor 11 are in a non-conducting state, it is a transistor.

signal voltage V at the collector of the transistor 11;

is equal to the DC voltage Vcc of the voltage supply terminal 31, and is the signal voltage V of the collector when the collector and emitter are in a conductive state.

is y = Vcc (V, -Vbe)R.

OR7 (7) is given by

Therefore, the signal voltage V at the collector of transistor 11
.

The amplitude of V. p-p is V□, -p=“901
．． It is expressed as 8°7.

However, by appropriately selecting the resistance values R7 and R8 of the resistors 19 and 20, the signal voltage V at the collector of the transistor 11 can be adjusted.

The amplitude of■. pp can be set to a sufficiently small value regardless of the magnitude of the signal voltage applied to the base of the transistor 10.

Therefore, transistors 10, 11 . Resistance 19-2
The circuit consisting of 2 operates as an amplitude control circuit.

The collector-emitter of the transistor 12 becomes conductive by grounding the control terminal 30, and the control terminal 3
By opening 0, it can become non-conductive.

However, it is clear that when the collector and emitter of the transistor 12 are non-conductive, the circuit 33 surrounded by the broken line described above operates simply as an active filter.

When the collector-emitter of the transistor 12 is conductive, the amplitude-limited signal at the collector of the transistor 11 is applied to the input terminal 4 of the amplifier 1 via the resistor 25.
At the same time, the DC voltage at the collector of transistor 11 ■.

is also applied. The signal at the collector of the transistor 11 applied to the input terminal 4 of the amplifier 1 is a positive feedback signal, and the circuit shown in FIG. 1 operates as an oscillator.

In this embodiment, an amplitude limiting circuit and a transistor switching circuit are added to the RC active filter satisfying the above-mentioned equations (1) to (5), and the filter is operated as an oscillator.

Furthermore, the oscillation frequency of this oscillator coincides with the center frequency of the filter.

Therefore, the oscillation frequency can be adjusted by changing the resistor R3 or R4 of the filter, the Q during oscillation can be adjusted by the resistor R5, and the gain can be adjusted by changing the resistor R1.

Moreover, these adjustments can be made very easily since each resistor can be trimmed independently.

Furthermore, by applying a DC voltage to the input terminal 4 of the amplifier 1, the rise time of oscillation can be extremely shortened.

Furthermore, this DC voltage is the collector DC voltage IEV of the transistor 11 that constitutes the amplitude limiting circuit.

and a signal voltage are superimposed, and the structure is such that this DC voltage is directly applied to the input terminal 4 from the amplitude limiting circuit via the switching transistor 12.

Therefore, in addition to shortening the oscillation start-up time, stable oscillation operation can be achieved in a short time.

FIG. 2a is a diagram showing the rise characteristic of oscillation of a conventional oscillator, and FIG. 2 is a diagram showing the rise characteristic of oscillation of the oscillator according to the present invention.

In an embodiment of the present invention, some of the resistors and capacitors are configured as thin film integrated circuits, and the amplifiers, transistors, and other resistors are configured as semiconductor integrated circuits, and further,
Both can be configured as a hybrid integrated circuit.

As described above, according to the present invention, it is possible to realize an active filter/oscillator that is used in selective calling devices such as mobile radio equipment and operates by switching between an active filter during reception and an oscillator with a shortened oscillation rise time during transmission. .

Further, according to the present invention, an active filter oscillator that can be manufactured as an integrated circuit can be realized.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an example of the present invention, and FIG. 2 is a diagram showing an example of the rise characteristic of oscillation, where a is a conventional example and b is an example according to the present invention. In Fig. 1, 1 to 3 are amplifiers, and 4 to 6 are amplifiers 1 to 3.
3 input terminals, 7-9 output terminals of amplifiers 1-3, 10
~12 is a transistor, 13-25 is a resistor, 26.27
is a capacitor, 28 is a signal input terminal, 29 is a signal output terminal, 30 is a control terminal, 31 is a voltage supply terminal, 32 is a common ground terminal, and 33 is an active filter.

Claims (1)

[Scope of utility model registration request] a first amplifier connected to the input terminal via a first resistance means; a second amplifier connected to the first amplifier via a second resistance means; an output terminal from which an output signal of the second amplifier is taken out; a third amplifier connected to the output terminal via a third resistor; the third amplifier and the first amplifier; a fourth resistance means connected between the amplifier;
a fifth resistance means connected in parallel to the first amplifier; a first capacitive element connected in parallel to the second amplifier; and a fifth resistor connected in parallel to the third amplifier. an active filter circuit having a band-pass characteristic including a sixth resistance means and a second capacitive element; amplitude limiting of the output signal from the active filter circuit and positive feedback to the input terminal of the active filter circuit; the positive feedback circuit has an amplitude limiting circuit that limits the amplitude of the couple signal; one end is connected to the output end of the amplitude limiting circuit, and the other end is connected to the active filter. and a switching transistor circuit to which the input end of the circuit is connected, and by turning on this switching transistor circuit during oscillation, both the output signal voltage and the DC voltage of the amplitude limiting circuit are set to the active state via the switching transistor circuit. An active filter oscillator characterized in that a voltage is applied to the input end of a filter.