JPS6328310B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drive circuit for a dynamically driven fluorescent display tube, and when dynamically driving (time-divisionally driving) a fluorescent display tube, at least one of a grating and an anode is connected to a display segment. It is an object of the present invention to provide a drive circuit that can shorten blanking time and improve brightness by substantially short-circuiting when electrically off.

For example, in an audio tape deck,
The VU
A spectrum analyzer may be provided along with the meter. Spectrum analyzers that use small, easy-to-read flat display elements, particularly those that use fluorescent displays with fast response speed and low driving voltage, are attracting attention. In order to display the spectral level using this fluorescent display, conventionally the X-Y
A matrix fluorescent display tube was used.

That is, in FIG. 1, the X-Y matrix fluorescent display tube has m rectangular anodes in the vertical direction, as shown by b ₁ to b _n , and n grids, shown as c ₁ to _{c o,} in the horizontal direction. are arranged in a matrix, respectively.
In addition, n rectangular phosphors are applied to each anode, corresponding to the grids c ₁ to _{c o} , respectively.
Display segments a ₁₁ to _{a no} of mn phosphors are formed. This X-Y matrix fluorescent display tube displays n frequency bands divided from low to high from left to right in the figure, and each frequency band is divided into n frequency bands from bottom to top in the figure. Displays values according to the level of the frequency band. For example, the display segments a ₁₁ to _{a n1 of} phosphors provided on the anodes b ₁ to b _n corresponding to the leftmost grating c 1 display the level of the lowest frequency band among the frequency bands to be displayed. However, if we assume that the required on-voltage (driving pulse) is applied to the grating c ₁ and the required on-voltage (driving pulse) is applied to the anodes b ₁ to b _x , then these anodes b ₁ The phosphor above ~b _x is brought to an excited state, and the display segments a ₁₁ to a _x1 formed by the phosphor become emissive as shown by diagonal lines in Figure 1, and the level of the lowest frequency band is shown as a bar graph. A similar bar graph display is performed for each of the other frequency bands, making it possible to immediately determine the frequency distribution of the input audio signal.

Such an X-Y matrix fluorescent display tube normally performs drive display by dynamic drive in which drive pulses are applied in a time-division manner. For example, when applying driving pulses to the grating of the fluorescent display tube 1 in a time-divisional manner, the grating of the fluorescent display tube 1 is applied as shown in FIG.
Driving pulses are applied alternately to c ₁ and c ₂ from field effect transistors Q ₁ and Q ₂ which operate as switching elements by input pulses from input terminals 2 and 3,
Among the anodes b ₁ to _{b 3} , display segments on the anode to which the driving pulse is applied are time-divisionally emitted.
At this time, the off-voltage is given a negative voltage -V _p by the pull-down resistors R ₁ and R ₂ .

By the way, the driving pulses applied to the gratings c ₁ and c ₂ of the fluorescent display tube 1 are applied to the equivalent capacitances between the grating and the cathode and between the gratings (C _x1 , C _x2
Even if the values of the pull-down resistors R ₁ and R ₂ are relatively small, the trailing edge (falling edge) of the pulse falls slowly due to the influence of the stray capacitance of the connection line, etc., as shown in Figure 3. A circuit delay time t ₁ occurs between the drive pulse applied to grating c ₁ shown in A and the drive pulse applied to grating c ₂ shown in B, and the rise of one of these drive pulses and the other If the falling edges are simultaneous, the drive pulses will be applied to gratings c ₁ and c ₂ at the same time for the delay time t ₁ as shown in FIGS. 3A and 3B. On the other hand, the above lattice c ₁ , c ₂ is also applied to anodes b ₁ to _{b 3}
Drive pulses representing level information in different frequency bands are applied in synchronization with the drive pulses to
As described above, when drive pulses are applied to gratings C ₁ and C ₂ at the same time, the level information of the two frequency bands is displayed overlappingly, and the display segment that must be erased is the level information of the adjacent frequency band. There is a possibility that the display will emit light and the display will not be accurate.

The above overlap of level information is called crosstalk, but conventionally, to remove this crosstalk, grid
The leading edge and/or trailing edge of the drive pulses c ₁ and c ₂ were cut off. Figure 4A,
B shows the drive pulse waveform of gratings c ₁ and c ₂ in which cut portions are provided at both the leading edge and the trailing edge for times t _B1 and t _B2 , and there is a cut time t _B between them, that is, There will be a blanking time.
This blanking time is determined in consideration of the circuit delay time _t1 , and is generally selected to be quite long, 10 μs or more.

However, since the repetition frequency of the drive pulse that dynamically drives the fluorescent display tube must be 150 Hz or higher due to the flicker limit of the human eye, once the number of gratings to be dynamically driven is determined, it must be kept constant accordingly. The upper limit of the drive pulse width is determined. For example, if the number of grids is 100,
The driving pulse width is approximately 67 μs (or less), and when the blanking time is set to 10 μs, the brightness decreases, and as the blanking time increases, the brightness decreases.

In this way, the blanking time is provided to eliminate the crosstalk, but it is generally quite long, 10 μs or more, and on the other hand, as the number of gratings and anodes to which driving pulses of the fluorescent display tube are applied increases,
The driving pulse width becomes narrower in inverse proportion to this, which reduces the duty factor for light emission of the display segment and further reduces the brightness, which leads to a drop in brightness that is practically unacceptable. It was hot.

The present invention eliminates the above-mentioned drawbacks, and one embodiment thereof will be described below with reference to FIGS. 5 to 8.

FIG. 5 is a circuit diagram showing the basic principle of the drive circuit of the dynamic drive type fluorescent display tube according to the present invention;
The figure shows a circuit diagram of an embodiment of a driving circuit for a dynamically driven fluorescent display tube according to the present invention. In FIGS. 5 and 6, the same parts as in FIG. 2 are designated by the same reference numerals, and their explanations will be omitted. In Figure 5, Q ₃ ,
_Q4 is a switching field effect transistor that operates complementary to _Q1 and _Q2 , and the input voltage from input terminals 2 and 3 is inverted in polarity by inverters 4 and 5 and applied to the gate. Therefore, when field effect transistor Q ₁ is on, Q ₃ is off, when Q ₁ is off, Q ₃ is on, and similarly for field effect transistors Q ₂ and Q ₄ , either one is on. when the other is off. As a result, during the period when no driving pulse is applied to the gratings c ₁ and c ₂ of the fluorescent display tube ₁ , the gratings c ₁ and _{c 2 are}
and cathode F are connected, and the two are substantially short-circuited.

By taking such measures, the capacitance C _x1 between the grating and the cathode etc. can be reduced by applying the driving pulse.
_{C _ _} is rapidly discharged through. Therefore, since the delay time t ₁ is extremely short, the blanking time of the drive pulses applied to the gratings c ₁ and c ₂ in a time-division manner is
It can be made much shorter than before. Therefore, the luminance of a fluorescent display tube having the same number of gratings and anodes as the conventional one increases because the duty factor of the luminescence becomes larger than that of the conventional one. In addition, if the number of gratings and anodes is small and the driving period (light-emitting period) by the dynamic driving pulse is relatively sufficiently large compared to the non-driving period (non-light-emitting period), the above-mentioned effect of improving brightness can be achieved. does not appear very conspicuously, but the influence of crosstalk does not become much of a problem when the time delay t ₁ is extremely small, so it has the advantage of eliminating the need for a circuit for creating a blanking time.

Note that if the time delay t ₁ is simply made smaller, a fixed resistor having a value approximately equal to the value of the on-resistance between the drain and source of the field effect transistor Q ₃ or Q ₄ is used as the pull-down resistor R ₁ , R _{2 may be used instead of 2} , but in this case, a large current flows through this fixed resistor when the field effect transistors Q ₁ and Q ₂ are turned on, causing a drop in the drive pulse level, large power consumption, and further is undesirable because it has an adverse effect on Q ₁ and Q ₂ . On the other hand, in this embodiment, Q ₃ and Q ₄ are off during the drive pulse application period, and their drain-source resistance shows the maximum value, so the above-mentioned adverse effects do not occur at all.

Next, to explain the circuit of this embodiment shown in FIG. 6, the operational amplifier A ₀ has its non-inverting input terminal supplied with the switch control signal V _1N from the input terminal 6.
The reference voltage from input terminal 7 is applied to the inverting input terminal.
_VR is supplied to it, and it operates as a comparator and has the same function as the field effect transistors Q ₁ and Q ₃ described above. Note that an operational amplifier having the same configuration as the above operational amplifier A ₀ is also connected to the input side of the grid c ₂ .
Illustrations are omitted.

Now, assuming that the level of the switch control signal V _1N is higher than the reference voltage V _R , the output of the operational amplifier A ₀ becomes a drive pulse of approximately +V _P , and the reference voltage V _R
When it is smaller than , the output becomes an off-voltage of approximately _-VN .

In this embodiment, in order to ensure electrical off, a cutoff voltage is applied between the electrical midpoint of the cathode F (center tap F _c of the transformer T) and the negative power supply for off voltage (-V _N ). A parallel circuit 8 of a Zener diode and a capacitor for creating Vcco is inserted and connected, but this does not in any way prevent the above-mentioned substantial short circuit between the grid and the cathode.

In the above embodiment, the fluorescent display tube 1 is provided with two gratings c ₁ and c ₂ and three anodes b ₁ to b ₃ , but as shown in FIG. A lattice c ₁ to _{c o} arranged in an X-Y matrix and an anode
When consisting of b ₁ to _{b n} , operational amplifiers having the same function as the above-mentioned operational amplifier A _p are provided on all input sides of the gratings c ₁ to _{c o} . Thereby, as explained in conjunction with FIG. 5, the brightness can be improved.

Furthermore, the above is an explanation of the so-called lattice blanking method in which blanking is applied to the grating drive pulse, but in the case of the so-called segment blanking method in which blanking is applied to the anode drive pulse, the lattice in the above explanation can be replaced with The same is true if an anode is used, in which case the circuit of the invention will essentially short-circuit the anode to the cathode. Furthermore, the grid blanking method and the anode blanking method can be used together, and in this case, the anode and the grid can each be short-circuited to the cathode.

FIG. 7 shows a circuit diagram of the main parts of a spectrum analyzer to which the circuit of the present invention is applied. In the same figure,
9 is the display surface of an X-Y matrix fluorescent display tube in which m anodes b ₁ to b _n and n gratings c ₁ to _{c o} are respectively arranged in a matrix as in FIG. ,
mn rectangular display segments a ₁₁ to a _no are formed, and each grid c ₁ to _{c o} of this fluorescent display tube
The configuration is such that the outputs of operational amplifiers A ₁ to _{A o} each having the same function as the operational amplifier A _p shown in FIG. 6 are applied. Switch control signals from input terminals 10 ₁ to 10 _o are applied to the non-inverting input terminals of the operational amplifiers A ₁ to A _o , and the same reference voltage V _R is simultaneously applied to their inverting input terminals. be done. In addition, _{the negative} power supply (−
V _N ) and the cathode of a fluorescent display tube having a display surface 9 are connected.

A signal to be spectrally analyzed by this fluorescent display tube, for example, an acoustic signal to be recorded, is divided into n different frequency bands by a filter circuit (not shown), and each frequency component signal is extracted. The signals are then rectified, smoothed, sampled and held, and applied to corresponding input terminals 11 ₁ to 11 _o , respectively. Among the different divided frequency band signals that enter the input terminals 11 ₁ to 11 _o , the divided frequency band signal with the lowest band comes to the input terminal 11 ₁ , and the following input terminals 11 ₂ , 11 ₃ , . . . 11 _o
It is assumed that a divided frequency band signal with the highest band is inputted to the input terminal _11o , and a divided frequency band signal with the highest band is inputted to the input terminal 11o. Input terminal 11
₁ to _11o are simultaneously applied to the multiplexer 12, where they are switched and only one input signal is sequentially and cyclically selected and outputted to the operational amplifier ₁₃₁ , which operates as a comparator. ~ _13n non-inverting input terminals are applied simultaneously. That is, multiplexer 12
The output signal is sent to the input terminals 11 ₁ to 1 at regular intervals.
Each input signal of 1 _o is 11 ₁ , 11 ₂ , ..., 11 _o ,
11 ₁ , 11 ₂ , . . . are taken out in sequence.

Different predetermined DC voltages are applied to each inverting input terminal of the operational amplifiers 13 ₁ to 13 _n by a level setting resistor network 14 formed by a plurality of resistors connected in series between a power supply and ground. Here, among a plurality of m of DC voltages taken out from the level setting resistor network 14, operational amplifiers 13 ₁ ,
It is applied to the inverting input terminals of 13 ₂ , . . . , 13 _n-1 , 13 _n . Therefore, none of the output signals of the operational amplifiers 13 ₁ to 13 _n are taken out when the divided frequency band signal level from the multiplexer 12 is the minimum, but when it is above a certain level, the output signals are output at a predetermined constant level depending on the level. The number of operational amplifiers from which the output signal is taken out is ₁₃ from the lowest to the lowest.
Alternatively, the output signals 13 ₁ and 13 ₂ are different, and when the input level is the maximum, output signals of a predetermined constant level are taken out from all of the operational amplifiers 13 ₁ to 13 _n . The respective output signals of these operational amplifiers 13 ₁ to 13 _n are separately applied as driving pulses to the anodes b ₁ to b _n of the fluorescent display tube.

On the other hand, since pulses smaller than the duty factor 1/n are input to the input terminals 10 ₁ to 10 _o in a time-division manner, the drive pulses taken out from the operational amplifiers A ₁ to A _o in a time-division manner The gratings c ₁ to c _o are sequentially driven in a time-division manner. At this time, the lattice c ₁ ~
During this period, the grids to which no drive pulse (on voltage) is input from the operational amplifiers A ₁ to _{A o} among c _o
It is substantially shorted to a cathode (not shown) as described in conjunction with FIG. Here, the above input terminal 10 ₁
The input period of the switch control signal to the input terminal 1 and the input signal passing period of the input terminal ₁₁ by the multiplexer 12 are both the same period, and similarly, the input period of the switch control signal to the input terminal 1
Each switch control signal input period of 0 ₂ to 10 _o and each input signal passing period of input terminals 11 ₂ to 11 _o by the multiplexer 12 are also synchronized.
Therefore, the level of the lowest divided frequency band signal input to the input terminal 11 ₁ is anode b ₁ , b ₂ , b ₃ , . . .
..., display segment a ₁₁ , a ₂₁ , a ₃₁ , ..., on b _n
a _n1 is displayed as a bar graph, and the input signal levels sequentially input to input terminals 11 ₂ to 11 _o-1 are displayed in a grid.
Display segments on anodes b ₁ to _{b n} provided corresponding to c ₂ to c _o-1 are sequentially time-divided and displayed as a bar graph, and the highest divided frequency band signal that has entered the input terminal 11 _o The levels of anodes b ₁ , b ₂ , ...,
A bar graph is displayed using display segments a _1o , a _2o , ..., a _no on b _n .

In this way, the input signal is time-divisionally displayed in level and spectrum for each frequency band divided into n. For example, the number of frequency band divisions n is 10.
The center frequency of the frequency band divided by 31.5Hz, 63Hz,
125Hz, 250Hz, 500Hz, 1kHz, 2kHz, 4kHz, 8k
Hz, 16kHz, and from 0dB with m as 13
In a spectrum analyzer that displays a level up to 24 dB in 2 dB steps, the duty factor of the dynamic drive is relatively large. It is also possible to eliminate the blanking time for the pulse width of each drive pulse c ₁ to c _o . This simplifies the circuit configuration.

Incidentally, in the above explanation, an X-Y matrix fluorescent display tube was used as an example of a dynamically driven fluorescent display tube, but any fluorescent display tube that can be dynamically driven may be used.For example, as shown in FIG. As shown, the anodes b ₁ ′, b ₂ ′, ... are connected to b ₁ ′ ~ b ₅ ′, b ₆ ′ ~
One grid c ₁ ′, c ₂ ′, c ₃ ′, ... is provided for each of the five anodes, such as b ₁₀ ′, b ₁₁ ′ to b ₁₇ ′..., and the grids c ₁ ′, c ₂ ′, c ₃ ′ have input terminals 14 ₁ , 14 ₂ , 14 ₃
Applying more time-division driving pulses, on the other hand, the anode
b ₁ ', b ₆ ', b ₁₁ ', ... are connected to the input terminal 15 ₁ , and anodes b ₂ ', b ₇ ', b ₁₂ ', ... are connected to the input terminal 15 ₂ , and the anode b ₃ ′, b ₈ ′, b ₁₃ ′, ...and b ₄ ′, b ₉ ′
，
B ₁₄ ′, . . . and b ₅ ′, b _{10 ′} , b _{15 ′} , _. A display tube may also be used. In FIG. 8, the drive pulses entering the input terminals 15 ₁ - 15 ₅ are switched in synchronization with the switching of the drive pulses at the input terminals 14 ₁ - 14 ₃ and change according to the input signal level. For example, a relatively high level input signal is applied to input terminals 15 ₁ to 15 ₅ during a period when a drive pulse is applied to input terminal 14 ₁ .
A driving pulse is applied to all of the anodes (i.e. display segments here) b ₁ ′ to b ₅ ′ to emit light,
The driving pulse application period from the next input terminal 14 ₂ is, for example, 15 among the input terminals 15 ₁ to 15 ₅ .
A drive pulse is applied only _to input terminals ₁ to 15 ₄ to cause display segments b ₆ ′ to _{b 9} ′ to emit _light . Since no drive pulse is applied to any of them, none of the display segments b ₁₁ ′ to b ₁₅ ′ emit light. Therefore, in the above case, due to the afterimage effect of the human eye, the display segments b ₁ ′ to _{b 9} ′ appear to be emitting light at the same time, and a bar graph is displayed. The circuit of the present invention can also be applied to such a bar graph fluorescent display tube.

Note that in the above embodiment, the operational amplifiers A _p ,
For A ₁ to A _o , a circuit configured to obtain an equivalent output may be used instead, such as an inverter or a logic circuit such as a buffer circuit. Furthermore, the dynamically driven fluorescent display tube described above can be used for applications other than spectrum analyzers, such as multi-channel meters.

As described above, the drive circuit for a dynamically driven fluorescent display tube according to the present invention applies drive pulses to the dynamically driven fluorescent display tube in a time-divisional manner to cause the dynamically driven fluorescent display tube to perform a light emitting display, and also to control the dynamically driven fluorescent display tube. The grating and/or anode of the optical display tube to which the driving pulse is applied are substantially connected to the cathode of the dynamically driven fluorescent display tube during the period when the driving pulse is not applied to the grating or the anode. Since the structure is configured to short-circuit the grid and release the short-circuit during the application period of the drive pulse to the grating or the anode, the circuit delay time of the drive pulse can be significantly reduced compared to the conventional method, so the blanking time can be reduced. It can be reduced to almost zero, so the duty factor for light emission can be increased compared to the conventional method, and the brightness can be improved. When using a spectrum analyzer, the number of divided frequency bands can be increased, allowing a more detailed spectral distribution to be seen. When performing light emitting display with the same brightness, the drive pulse voltage can be set low, the power supply circuit and drive circuit can be constructed at low cost, and furthermore, they can be constructed using operational amplifiers.
It can be integrated into an IC, and as a result, it can be made into a small and inexpensive configuration, making it easy to use in a built-in spectrum analyzer such as an audio cassette deck. When applied to a spectrum analyzer with about 7 to 10 frequency bands, the dynamically driven duty factor can be relatively large, so the blanking time can be reduced to almost zero. It has many features such as eliminating the need for a blanking generation circuit, simplifying the circuit, and preventing current from flowing between the grid and cathode during the lighting period, preventing wasteful power consumption. It has the following.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing a schematic configuration of a general X-Y matrix fluorescent display tube, Fig. 2 is a circuit diagram showing an example of a conventional circuit, Figs. 3A and B and Figs. 4A and B are respectively 5 is a circuit diagram for explaining the basic principle of the circuit of the present invention, FIG. 6 is a circuit diagram showing an embodiment of the circuit of the present invention, and FIG. 7 is a diagram showing the circuit of the present invention. FIG. 8 is a circuit diagram showing an embodiment of the essential parts of a spectrum analyzer to which the present invention is applied. FIG. 8 is a diagram showing an example of a schematic configuration of the essential parts of a bar graph fluorescent display tube to which the circuit of the present invention can be applied. 1... Fluorescent display tube, 6,10 ₁ to 10 _o ... Switch control signal input terminal, 7... Reference voltage input terminal, 9... Display surface of X-Y matrix fluorescent display tube, 11 ₁ to 11 _o ……Divided frequency band signal input terminal, 13 ₁ ~ 13 _o …… Operational amplifier, a ₁₁ ~ a _no ……
Display segment, b ₁ to b _n ...anode, c ₁ to c _o ... grating, F... cathode, A _p , A ₁ to _{A o} ... operational amplifier for driving pulse output and grating-cathode short circuit.

Claims (1)

[Claims] 1. Applying driving pulses to a dynamically driven fluorescent display tube in a time-divisional manner to perform a luminescent display, and at the same time applying the driving pulses to the grating and/or the anode of the dynamically driven fluorescent display tube. one is substantially short-circuited to the cathode of the dynamically driven fluorescent display tube during periods when the driving pulse is not applied to the grating or anode, and during the period when the driving pulse is applied to the grating or anode. A drive circuit for a dynamically driven fluorescent display tube, characterized in that it is configured to cancel the short circuit.