JPS6214773Y2 - - Google Patents

Description

[Detailed explanation of the idea]

This invention relates to a compact and economical push-button dial, which uses a key switch with a particularly simple contact configuration, provides stable operation even for long-distance subscribers, and eliminates harmonic components of digital push-button signals. The present invention relates to a push button dial having a push button oscillation circuit that can be removed by an IC. A push-button dial is used in push-button dial telephones, etc., and is a dial consisting of an oscillation circuit and a key switch to display numbers, etc. by combining relatively low-frequency signals and relatively high-frequency signals. In the case of button dial telephones, the relatively low frequencies are called the low group, and the relatively high frequencies are called the high group, consisting of 4 frequencies in the low group and 3 frequencies in the high group.
This figure represents a generator that generates a two-frequency hybrid signal corresponding to each of the 12 button numbers or symbols of a key switch in combinations (4 x 3) of one frequency per high group. Now, the oscillation circuit of the conventional push button dial is
LC (L: coil, C: capacitor) or RC
It consists of an oscillator (R: resistor, C: capacitor).The oscillation frequency is adjusted by adjusting the core in the LC type, and by trimming the resistor R of the thin film RC in the RC type. In addition, the frequency switch of the key switch that determines the low group and high group frequencies corresponding to the 12 push buttons is connected to the frequency determining element LC.
Or, since it is directly related to RC, the oscillation frequency changes depending on the magnitude or change of the contact resistance between the frequency switch contacts, and the chattering or instantaneous interruption of the switch contacts adversely affects the receiver and causes erroneous connections. Furthermore, since the frequency determining section is separated into a high group and a low group, the frequency switch has a two-make contact configuration. For these reasons, key switches are complex, have strict requirements, and have little economic merit. and,
The LC type push button dial has the disadvantage that it has a large shape and cannot be made smaller. Next, the oscillation circuit of the conventional digital push button dial has a three-terminal configuration in which the constant voltage circuit and the output circuit of the oscillation section are connected in parallel, and the output signal is taken out via the signal output buffer, and is connected to the line. In order to send a signal, a resistor is inserted between one terminal of the signal output buffer and the output circuit of the oscillation section, and the three terminals -
Two-terminal conversion is performed, but since the constant voltage circuit is connected in parallel with the output circuit of the oscillator, the current from the line is shunted to the constant voltage circuit and the output circuit, so a large amount of current is consumed. Otherwise, the operation of the constant voltage circuit and the output circuit will not be maintained, resulting in power loss. Therefore, a large amount of current is required from the line, and if the distance is long, the current is insufficient, so control is given to the subscriber line length. In addition, since the signal waveform is a step-like approximate sine wave, high frequency components are generated, and although distortion in the push button signal band is satisfied, distortion outside the signal band does not meet regulations. In order to solve these problems, this invention adopts a key input circuit and a switch additional circuit in the oscillation circuit of the pushbutton dial to alleviate the demands on the switch such as contact resistance and chattering, and has a simple one-make contact. Enables the use of a key switch in the configuration,
A reference clock generation circuit is used to stabilize the frequency, a low-pass filter is used to remove harmonic components, and the output stages of the output circuit and constant voltage circuit are stacked, and an output load circuit is installed between the output circuit and the constant voltage circuit. This is to prevent a drop in the power utilization rate from the line due to 3-terminal to 2-terminal conversion by connecting the push button dial, and its purpose is to make the push button dial more compact, more economical, and improve its performance. This invention will be explained below with reference to the drawings. FIG. 1 is a block diagram showing one embodiment of this invention. In this figure, 1 is a key switch, 2 is a reference clock generation circuit, 3 is a key input circuit, 4 is a switch addition circuit, and 5 is a frequency selection circuit, which is composed of a key decoder 6 and a programmable counter 7. 8 is an approximate sine wave generating circuit, which is composed of a hexadecimal counter 9, a decoder 10, a ROM, and a DA converter 11. 12 is a mixer, 13 is an output circuit including a low-pass filter, and 13a
is an input terminal for inputting the output from the mixer 12, 13b is an output terminal, 13c is a power supply terminal, 14
1 is an output load circuit consisting of a resistor, 15 is a constant voltage circuit, 15a to 15c are first to third constant voltage output terminals, 15d is an earth terminal, and _P1 to _P3 are dial signal output terminals. It is. In FIG. 1, from the frequency selection circuit 5 to the ROM and DA converter 11
The upper half of each block is for the low group, and the lower half is for the high group, and the operations and effects are exactly the same except that the number of division stages of the programmable counter 7 is different. Terminals P ₁ and P ₂ are dial signal output terminals that are passed through the telephone circuit or connected directly to the line during dialing, and terminal P ₃ represents the three-terminal configuration of the push button oscillation circuit together with terminals P ₁ and P ₂ . , 3-terminal to 2-terminal conversion is performed via the output resistor 14. Next, the operation and effect of the push button oscillation circuit will be explained. When any button on key switch 1 is pressed to make a dial call, first, the common contact (not shown) of key switch 1 applies power V _MF between terminals P ₁ and P ₂ , and reference clock generation circuit 2 is activated. to generate a reference clock. Reference clock generation circuit 2
It consists of an oscillator with a high frequency and high precision frequency, an oscillation circuit, and a frequency divider called a prescaler, and generates a reference clock. In consideration of versatility, a color television crystal (oscillation frequency: 3.579545 MHz) is used for the resonator, and the frequency is divided by four using a prescaler to generate a reference clock of 894,886.25 Hz. When the frequency contact of the key switch 1 operates in this state, the low group input terminal L ₁ of the key input circuit 3 is activated in response to any one button.
~ _L4 and one of the input terminals _H1 ~ _H3 of the high group generate frequency contact information. FIG. 2 shows the key input circuit 3. A circuit corresponding to one frequency each of the low group and the high group will be explained.
Low group has 11 NPN transistors Tr, high group has PNP
Consisting of one transistor Tr2 and one NPN transistor Tr3, the low group contact of the frequency switch _SW is connected to the base of the low group transistor Tr1, and the frequency switch _S is connected to the base of the high group transistor Tr2.
The high group contacts of _W are connected respectively. In addition, since the power supply V _c is connected to the emitter of transistor Tr2 in the high group, when the contact of frequency switch _SW is closed, the emitter of transistor Tr2 → base → contact of frequency switch _SW → transistor Tr
Current flows from the base of 1 to the emitter, and the three transistors Tr1 to Tr3 in both groups are turned on, and the terminals
Contact information at both ends can be obtained from L′ ₁ and H′ ₁ . Frequency switch _SW contacts are two transistors
Since it is placed between the bases of Tr1 and Tr2, the key input circuit 3 operates even if the contact resistance of the contact of the frequency switch _SW becomes large. The above explanation is □1 in Figure 1.
However, as shown in FIG. 2, terminals L ₂ to _{L 4} of the low group and terminals H ₂ to _{H 3} of the high group are added to form the entire configuration. Lc and Hc are common information for low and high groups. With the above configuration, the frequency switch _SW of the key switch 1 can have only one contact point. Contact information from the key input circuit 3 is input to the switch addition circuit 4. A reference clock is also input to the switch addition circuit 4. The switch addition circuit 4 is composed of a contact information monitoring circuit and a contact information holding circuit, monitors and holds the contact information for a certain period of time after chattering ends, and outputs the contact information to the key decoders 6 of the low and high groups. FIG. 3a shows the low group block diagram of the switch addition circuit 4 and the common contacts of the key switch 1. In this figure, L' ₁ to L' ₄ are low group frequency contact information input to the switch addition circuit 4, G ₁ and G ₂ are gate circuits, T is a contact information monitoring circuit, and POR is a direct current input by the common switch C _SW . A power-on reset circuit that operates when the voltage V _MF is applied, M _L1 to M _L4 are storage circuits for contact information, and G _L1 to _{G L4} are storage circuits M for storing the low group frequency contact information L' ₁ to L' ₄ . _L1 to M _L4 are gate circuits controlled by the contact information monitoring circuit T, and f _L1 to f _L4 are the outputs of the switch addition circuit 4. Next, the operation will be explained. When any one of the 12 buttons on the push button dial is pressed, a voltage V _MF is applied by the common switch C _SW . This will reset the power-on reset circuit.
POR directly resets the contact information monitoring circuit T and memory circuits M _L1 to M _L4 through gate _G2 . At this time, any one of the four inputs (for example,
L′ ₁ ) When contact information appears, this contact information operates the contact information monitoring circuit T through gates G ₁ and G ₂ , and the contact information monitoring circuit T receives the low group frequency contact information.
After a period of time long enough to sufficiently absorb the chattering of L' ₁ , a signal to open the gates is sent to the gate circuits G _L1 to G _L4 . Only the gate circuit G _L1 operates according to the low group frequency contact information L' ₁ and the signal from the contact information monitoring circuit T, and transmits the low group frequency contact information L' ₁ to the storage circuit M _L1 . The memory circuit M _L1 stores this information and outputs the output f _L1 of the switch addition circuit 4, and at the same time resets the contact information monitoring circuit T through the gate _G2 and closes all gate circuits G _L1 to _{G L4} . Therefore, the output f _L1 retains the information stored in the memory circuit M _L1 and is completely separated from the low group frequency contact information L' ₁ . This condition continues until the pushbutton is restored, the common switch C _SW is restored, and the voltage V _MF is removed. Note that the configuration and operation are the same for the high group, so a description thereof will be omitted. FIG. 3b is a waveform diagram for explaining the operation of the switch addition circuit 4. FIG. At time t ₀ , voltage V _MF is applied between terminals P ₁ and P ₂ , and at time t ₁ , the frequency switch is applied.
When any one contact of _{the SW} operates, the contact operation of that contact causes chattering to continue until time _t2 .
It is stable from time t ₂ to t ₄ , momentary interruption occurs from time t ₄ to t ₅ , stable from time t ₅ to t ₆ , and from time t ₆
The contact of the frequency switch _SW becomes open. On the other hand, the output of the switch addition circuit 4 is not generated while chattering occurs (between _t1 and _t2 ). If the stable state continues for more than the monitoring time of the contact information monitoring circuit (t ₃ - t ₂ ) after the chattering ends and becomes stable, contact information is detected and held (t ₄ ). Once held, the held state is maintained regardless of the input information, and continues until time _t7 when the voltage _VMF between terminals _P1 and _P2 is removed. The switch addition circuit 4 not only prevents chattering and instantaneous interruption of the frequency switch, but also has the effect of preventing malfunction due to induced noise and the like. Referring again to FIG. 1, the frequency selection circuit 5 selects the low group and high group frequencies corresponding to the contact information.
The frequency selection circuit 5 is composed of a key decoder 6 and a programmable counter 7, and the key decoder 6 inputs one input information from the switch addition circuit 4 into the programmable counter 7 for each low and high group to obtain a desired frequency division number. The code is converted between the circuit 4 and the programmable counter 7, and the programmable counter 7 divides the reference clock based on the contact information code-converted by the key recorder 6, and divides the frequency of the reference clock to 14 times the signal frequency of the low and high groups corresponding to the contact information. Outputs the clock pulse. The 14 times the clock pulse is used to construct an approximate sine wave to be described later (clock pulses L ₀ , H ₀ ). Table 1 shows the frequency division numbers N _L and N _H of the low group and high group of the programmable counter 7, and the clock pulse.
Signal frequencies _L , _H , which are obtained by dividing L ₀ and H ₀ by 14,
Furthermore, the deviation of this signal frequency from the push button signal frequency nominal values _LN , _HN ( _L / _LN , _H / _HN
It represents. However, the values in Table 1 are when the frequency division numbers of the frequency prescaler of the crystal resonator, the programmable counter 7, and the hexadecimal counter 9 described below are taken as nominal values.

[Table] The approximate sine wave generation circuit 8 in Fig. 1 includes a hexadecimal counter 9, a decoder 10, a ROM, and a DA converter 1.
1, and 7 types per cycle from the clock pulse L ₀ (H ₀ ) which is the output of the programmable counter 7.
Create a 14-step stepped current approximate sine wave. Programmable counter 7 clock pulse L ₀
(H ₀ ) is divided by the hexadecimal counter 9, and output lines _la , l _b , l _c , l _d ( _ha , h _b ,
h _c , h _d ). This binary information is code-converted by the decoder 10, and the information appears on only one of the output lines _l1 to _l7 ( _h1 to _h7 ) for each count of 1 to 14. The ROM and DA converter 11 have DA converters 1, 4, 8,
One or more combinations of four constant current circuits of three types weighted at a ratio of 8 are operated to generate a current approximate sine wave of one period between 14 time slots (L _SG , H _SG ). In addition, the DA converter sets the current value of the constant current circuit to a slightly different value for the low group and high group, so that H _SG −L
Set the high group level high by setting _SG = 1 to 2 dB. FIG. 4 shows waveforms of various parts of the circuit for basic waveform formation of the low group of the approximate sine wave generating circuit 8, and the symbols correspond to those in FIG. 1. The approximate sine waves generated by the four constant current circuits are symmetrical about the seventh, and the weighting is 1, 4,
8, 13 (=1+4+8), 17 (=1+8+8), 20
It consists of 7 stages: (=4+8+8) and 21 (=1+4+8+8). The mixer 12 in FIG. 1 is a current summation circuit that adds the current approximate sine waves _LSG and _HSG of the low group and high group and outputs the result as a two-frequency current hybrid signal _iMF . Output circuit 13 including a low-pass filter
The input signal i _MF is amplified by a current amplifier, and the current −
The voltage is converted, harmonic components are removed by a low-pass filter, and a two-frequency voltage signal _vMF is sent to the line between terminals _P1 and _P2 . As is clear from the waveform of the current approximate sine wave _LSG in Figure 4, this signal contains harmonic components.
The level attenuation of the dominant order, the fundamental wave, is 14n±1, and the attenuation is 20log1/(14±1) (n is a natural number). On the other hand, the distortion attenuation of push button signals is specified to be 20 dB or more, and the harmonic components are specified as 20 dB in the 4KHz to 8KHz band and 20dB in the 8KHz to 12KHz band. It is 40dB and 60dB or more in each 3KHz band above 12KHz, and the distortion in the push button signal band is satisfied with a first-order low-pass filter, but it is not satisfied with the components outside the signal band. In order to reduce this component and satisfy the regulations, the buffer of the output circuit was made into a multi-stage emitter follower, this was combined with a CR, and a 3rd-order active low-pass filter was integrally constructed. The output resistor 14 determines the output impedance of the push button oscillation circuit and performs three-terminal to two-terminal conversion of the push button oscillation circuit. The constant voltage circuit 15 has a first constant voltage output terminal 15a that outputs a first constant voltage _Vc , a second constant voltage output terminal 15b that outputs a second constant voltage _Vref , and a third constant voltage _VLp .
It consists of a circuit that outputs three types of constant voltages, a third constant voltage output terminal 15c that outputs _g , and stabilizes each part of the push button oscillation circuit, so that the push button can be operated at a constant level regardless of the length of the line. generate a signal. In addition, since the output circuits are stacked on the constant voltage circuit 15 and connected in series, the current of the output circuit is also used in the constant voltage circuit 15, and there is no power loss compared to the conventional method in which the constant voltage circuits 15 are not stacked. . In other words, since the current from the line is not shunted like in the past, operation of both circuits is guaranteed even with a small current, making it stable even for long-distance subscribers.
A reliable dialing operation can be provided. The current approximated sine wave signal i _MF from the mixer 12 is converted to voltage in the output circuit, becomes a smooth sine wave in the low-pass filter, has a signal level determined by the output resistor 14, and is sent to the terminal as a two-frequency voltage signal v _MF . from P ₁ -P ₂ via the telephone circuit or directly to the line. Hereinafter, an example of a specific circuit of the output circuit 13 of FIG. 1 will be explained with reference to FIG. 5, and an example of a specific circuit of the constant voltage circuit 15 will be explained with reference to FIG. 6. FIG. 5 shows an example of the output circuit 13. 13a is the input of the current approximate sine wave signal _iMF from the mixer 12, 13b and 13c are terminals, 13d is a resistor for voltage conversion of the _iMF signal, 13e, 13f,
13i is a resistor, 13g, 13h are capacitors,
13j is a transistor, and the above constitutes an active low-pass filter. i _MF signal of output circuit input 13a is connected to resistor 13d
The signal is converted into a voltage waveform by a low-pass filter, high-frequency distortion is attenuated, and outputted from the output 13b via _P1 . The level of the output signal _VMF is amplified and outputted by an amplifier composed of a resistor 13i, a transistor 13j, and an output resistor 14, but the _VMF level is determined by the stabilized output voltage of the constant voltage circuit 15, _Vref and ROM and DA converter 11 by _Vc ,
Since the mixer 12 is stabilized, the i _MF signal level is constant, the input 13a of the output circuit 13 and the signal D at the output 13b are constant, and the DC voltage V _MF (line current I _L ) at the terminal P ₁ changes. Even if V _ref and V _c of the constant voltage circuit 15 do not change, the output signal V _MF is always output at a constant level. The output resistor 14 determines the gain of the amplifier of the output circuit (resistor 14/resistor 13i). Also,
Since the AC impedance of the transistor 13j is sufficiently high, the impedance of the circuit viewed from the P ₁ -P ₂ terminals is determined by the resistor 14. The output circuit 14 is connected in series with the constant voltage circuit 15 to improve the constant current operation of the dial circuit. For example, the output circuit 14 and the constant voltage circuit 15
Assuming that the starting current for each is 15 mA, the starting current for the entire circuit is 30 mA in the conventional parallel connection method of the output circuit and constant voltage circuit, but the series connection method of the output circuit and constant voltage circuit shown in Figure 5 In this case, the current from the output circuit will be reused by the constant voltage circuit, and the starting current will be 15mA. In the constant voltage circuit 15 shown in FIG. 5, 15e and 15f are Zener diodes, 15g is a resistor, and 15h is a diode. Therefore, stable operation is guaranteed even under conditions of low line current, ie, for subscribers located far from the telephone office. As explained in detail above, the push button dial according to this invention allows the use of a simple key switch with a one-make contact configuration using the key input circuit, and has the effect of preventing chattering and instantaneous interruption of the key switch using the switch additional circuit. In addition, by removing harmonic components of the approximate sine wave push button signal using an active low-pass filter, it is possible to satisfy the specifications for the signal band and out-of-band transmission level, and the output circuit and constant voltage circuit can be stacked. Since they are connected in series, the current from the output circuit is also used in the constant voltage circuit, which reduces power loss and improves power utilization compared to conventional systems that do not stack constant voltage circuits. Therefore, a small amount of current can be used effectively, and stable push-button dialing can be provided even to long-distance subscribers. Furthermore, the push button oscillation circuit can be implemented as a single chip IC by externally attaching the crystal oscillator of the reference clock generation circuit and the capacitor of the low-pass filter, and configuring each block with bibolar. It has the advantage of being smaller, more economical, and improving performance.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a push button dial showing an embodiment of this invention, Fig. 2 is a diagram showing a key input circuit, and Figs. 3a and b are block diagrams showing an example of a switch additional circuit and its input. Output waveform diagram, 4th
The figure is a time chart of the approximate sine wave generation circuit, No. 5
The figure shows a specific circuit of the output circuit, and FIG. 6 shows a specific circuit of the constant voltage circuit. In the figure, 1 is a key switch, 2 is a reference clock generation circuit, 3 is a key input circuit, 4 is a switch addition circuit, 5 is a frequency selection circuit, 6 is a key decoder, 7
is a programmable counter, 8 is an approximate sine wave generation circuit, 9 is a hexadecimal counter, 10 is a decoder, 11
is the ROM and DA converter, 12 is the mixer, 1
3 is an output circuit including a low-pass filter; 1
4 is an output resistor, and 15 is a constant voltage circuit.

Claims (1)

[Scope of utility model registration request] A key switch having a frequency switch with a make contact configuration, a reference clock generation circuit, a key input circuit in which one of the low group and the high group is selected by the key switch, and a switch additional circuit for eliminating chittering in the output of this key input circuit. a frequency selection circuit that outputs a pulse n times the frequency of the sine wave signal corresponding to one of the selected low group and high group, respectively; and a push button oscillation circuit section consisting of an approximate sine wave generation circuit that generates a sine wave that approximates the high group signal, and a mixer circuit that mixes the low group and high group signals, and a high frequency component of the output of the mixer circuit. an output circuit including a low-pass filter for removing the oscillation, a constant voltage circuit connected in series to the output circuit so as to be stacked thereon and supplying driving power to each circuit of the push button oscillation circuit section, and an output terminal of the output circuit. and an output load circuit connected between the first constant voltage output terminal of the constant voltage circuit, and a dial signal is extracted from between the output terminal of the output circuit and the earth terminal of the constant voltage circuit. A push-button dial that features a constant output level.