JP2758852B2 - Triangular wave oscillation circuit and video signal processing device having the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a triangular wave oscillating circuit for use in a stabilized switching power supply and a video apparatus having the same.

[0002]

2. Description of the Related Art Generally, a portable television receiver,
2. Description of the Related Art In a video tape recorder (hereinafter abbreviated as "VTR") and an electronic device such as a telephone, a power supply circuit based on a switching stabilized power supply system is frequently used in order to ensure stable operation and high efficiency of the electronic device. FIG. 5 shows such a portable VT.
FIG. 3 is a block diagram illustrating a configuration around a power supply circuit of R1.

The VTR 1 includes a power supply circuit 10 based on a switching stabilized power supply system, a video signal processing circuit 11 for performing signal processing of an input video signal, and a monitor control circuit 12 for controlling a monitor screen. The circuit 11 and the monitor control circuit 12 are supplied with power from the power supply circuit 10 via power supply lines La and Lb, respectively.

The power supply circuit 10 includes a triangular wave oscillation circuit 21 for outputting a triangular wave voltage, pulse width control circuits 23a and 23b provided corresponding to the power supply lines La and Lb, switching transistors 24a and 24b, and a smoothing circuit 25, respectively.
a, 25b. A pulse width control circuit 23a,
23b has two comparators 26a, 27a;
b, 27b.

[0005] Hereinafter, a description will be given of the construction and operation provided in correspondence to the power supply line La of the power supply circuit 10. In the comparator 26a of the pulse width control circuit 23a, the smoothing circuit 2
The output voltage 5a is compared with the reference voltage of the reference voltage 28. In the comparator 27a, the output voltage of the comparator 26a is compared with the triangular wave voltage from the triangular wave oscillator 21, and a pulse signal whose pulse width is controlled according to the comparison result is supplied to the switching transistor 24a. Smoothing circuit 25a
Then, the switching output according to the switching operation of the switching transistor 24a is smoothed, and the power supply line L
a is supplied with a stabilized power supply voltage.

The structure of the triangular wave oscillator 21 is shown in FIG.
Since the internal impedance of the self-propelled triangular wave oscillator 21a and the triangular wave oscillator is high as shown in FIG. This circuit configuration is already known, and is described in "Linear IC Practical Circuit Manual" by Yojiro Yokoi. Therefore, detailed description is omitted.

The configuration and operation corresponding to power supply line Lb are the same as the configuration and operation provided corresponding to power supply line La described above. Thus, the video signal processing circuit 1
1 and the monitor control circuit 12 are powered by the stabilized power supply voltage.

[0008]

However, in the triangular wave oscillating circuit 21 in such a switching stabilized power supply type power supply circuit, the input voltage range of the comparators 27a and 27b is finite, and the triangular wave There is a problem that it is necessary to adjust the variable resistor 21c to adjust the level. Also, since there is no external input control terminal, there is a problem that synchronization with an external clock cannot be obtained.

The video signal processing circuit 11 operates using a clock from the oscillator 29 having an oscillation frequency of 3.58 MHz as a reference clock, but this reference clock is not synchronized with the noise synchronized with the switching operation described above. Therefore, there is a problem that beat noise may occur.

The present invention has been made in view of the above problems, and has as its object to provide a triangular wave oscillating circuit which can synchronize with an external clock and can oscillate a triangular wave with a stable amplitude.

[0011]

According to a first aspect of the present invention, a triangular wave oscillating circuit compares a capacitor, a current source for charging and discharging the capacitor, and a voltage output of the capacitor with a predetermined reference level. A first comparator for synchronizing the reference voltage with an external clock signal to output a reference voltage different from the reference level;
Switching means for alternately switching and outputting the first voltage and the second voltage, a second comparator for comparing the output of the switching means with the output voltage of the capacitor, and an output of the second comparator. A flip-flop that inputs to a set terminal and connects the output of the first comparator to a reset terminal, and controls charging and discharging of the capacitor by the current source according to the output of the flip-flop. It is assumed that.

According to a second aspect of the present invention, the switching means includes a first resistor having one end connected to a power supply, a second resistor having one end grounded, and a second end connected to the other end of the first resistor. A third resistor connected to the other end of the second resistor, a means for extracting an output voltage from a connection point between the first resistor and the third resistor,
A collector terminal is connected to a connection point between the second resistor and the third resistor, an emitter is substantially grounded, and an external
Switch whose ON / OFF is controlled according to the clock signal
And a switching transistor .

According to a third aspect of the present invention, the output voltage of the switching means when the switching transistor is turned on is set higher than the reference level of the first comparator.

[0014]

According to the above construction, the current source charges and discharges the capacitor, the first comparator compares the voltage output of the capacitor with a predetermined reference level, and the switching means synchronizes with the external clock signal. To switch the reference voltage and output it.
The second comparator compares the output of the switching means with the output voltage of the capacitor, inputs the output of the second comparator to the set terminal, and connects the output of the first comparator to the reset terminal. Since a flip-flop is provided to control charging and discharging of the capacitor by the current source in accordance with the output of the flip-flop, synchronization with an external clock can be obtained and triangular wave oscillation with a stable amplitude can be performed.

According to a second aspect of the present invention, the switching means includes a first resistor having one end connected to a power supply and a second resistor having one end grounded.
, A third resistor connected to the other end of the first resistor and the other end of the second resistor, and an output voltage from a connection point between the first resistor and the third resistor. Means, and a switching transistor having a collector terminal connected to a connection point between the second resistor and the third resistor and having an emitter substantially grounded, and having an ON / OFF control in response to an external clock signal. Therefore, synchronization with an external clock can be obtained, and triangular wave oscillation with a stable amplitude can be performed.

According to the present invention, the output voltage of the switching means when the switching transistor is turned on is set higher than the reference level of the first comparator. Since one comparator does not operate, it is possible to synchronize with an external clock and perform triangular wave oscillation with a stable amplitude.

[0017]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention. In the present embodiment, a case where the present invention is applied to a portable VTR 31 will be described.

The VTR 31 includes a power supply circuit 40 using a switching stabilized power supply system, a video signal processing circuit 41 for performing signal processing of an input video signal, and a monitor control device 42 for controlling a monitor screen. The video signal processed in 41 is supplied to the monitor control circuit 42. The video signal processing circuit 41 and the monitor control circuit 42 are powered by the power supply circuit 40 via power supply lines La and Lb, respectively. In this embodiment,
The video signal processing circuit 41 will be described as a synchronization circuit.

The power supply circuit 40 includes a triangular wave oscillation circuit 51 for outputting a triangular wave voltage, pulse width control circuits 53a and 53b provided corresponding to the power supply lines La and Lb, switching transistors 54a and 54b, and a smoothing circuit 55.
a and 55b and a frequency dividing circuit 62. The pulse control circuits 53a and 53b each include two comparators 56
a, 57a; 56b, 57b.

The video signal processing circuit 41 operates using the oscillation frequency of the oscillator 60 having the oscillator 59 = 3.58 MHz as a reference clock. On the other hand, the reference clock from the oscillator 60 is provided to the frequency dividing circuit 62, and is subjected to １ ／ frequency division to the triangular wave oscillator 51.

Hereinafter, the configuration and operation of power supply circuit 40 provided corresponding to power supply line La will be described.

The comparator 56a of the pulse width control circuit 53a compares the output voltage e of the smoothing circuit 55a with the reference voltage Vo of the reference power supply 58. In the comparator 57a, the comparator 5
6a is compared with the triangular wave voltage C from the triangular wave oscillating circuit 51, and the comparator 57a
Is controlled, the pulse signal h smoothes the switching output in response to the switching operation of the switching transistor 54a, and supplies a stabilized power supply voltage to the power supply line La.

The switching transistor 54a has a PN
It is composed of a P-type transistor.
Are connected, and the collector is connected to the smoothing circuit 55a.
When the pulse signal h from the pulse width control circuit 53a is applied to the base of the switching transistor 54a, the power supply voltage of the power supply 63a is turned on / off in response to this and is applied to the smoothing circuit 55a.

The smoothing circuit 55a includes a Schottky diode 71a, a choke coil 72a, and a capacitor 73.
a. The cathode of Schottky diode 71a is connected to the collector of switching transistor 54a, is connected to one end of choke coil 72a, and the anode of diode 71a is grounded. The other end of the choke coil 72a is grounded via a capacitor 73a. The other end of the choke coil 72a is connected to the power supply line La and to the non-inverting input terminal of the comparator 56a. Thus, the output voltage c is supplied to the power supply line La from the connection point between the choke coil 72a and the capacitor 73a as a power supply voltage, and is fed back to the non-inverting input terminal of the comparator 56a as a comparison voltage.

FIG. 2 is a waveform diagram for explaining the operation. FIG. 2A shows an output voltage e from the smoothing circuit 55a.
Is shown. In FIG. 2B, the waveform of the output voltage f of the comparator 56a is indicated by reference numeral f, and the waveform of the triangular wave voltage C is indicated by reference numeral C. (2) and (3) in FIG.
When the triangular wave voltage C is larger than the output voltage f, the output h of the comparator 57a goes low, turning on the switching transistor 54a to supply the power supply voltage from the power supply 63a to the smoothing circuit 55a.

On the other hand, when the triangular wave voltage C is smaller than the output voltage f, the output h becomes H level, and the supply of the power supply voltage from the power supply 63a is stopped. That is, the power supply 63a
Is proportional to the falling width of the pulse of the output h.

For example, when the output voltage e decreases as indicated by reference numeral d in FIG. 2A, the comparator 56a
(F) corresponds to the output f (see (2) in FIG. 2), and accordingly, the pulse fall width tb of the output h is larger than the normal fall width ta. In response, the output voltage e slightly rises.
As described above, the output voltage e is controlled so as to be always constant.

The configuration and operation corresponding to power supply line Lb are the same as the configuration and operation provided corresponding to power supply line La described above .
The symbol “b” is attached. Thus, the video signal processing circuit 4
1 and the monitor control circuit 42 are powered by the stabilized power supply voltage.

FIG. 3 is a block diagram showing the configuration of the triangular wave oscillation circuit 51, and FIG. 4 is a waveform diagram for explaining the operation thereof. The triangular wave oscillation circuit 51 includes a charge / discharge circuit 81 that outputs a triangular wave voltage C by selectively switching between a charging operation and a discharging operation, a reference voltage switching circuit 82 that can selectively switch between two reference voltages, The first and second comparators 83 and 84 and a flip-flop 85 that controls the charge / discharge circuit 81 according to the output of each of the comparators 83 and 84 are configured.

The charging / discharging circuit 81 includes a first current mirror circuit 94 including three PNP transistors 91, 92, and 93, a second current mirror circuit 97 including two NPN transistors 95 and 96, and a charging / discharging circuit 81. And a discharging capacitor 98. The transistor 9
The emitter area of the transistor 6 is set to twice the emitter area of the transistor 95.

The emitters of the transistors 91, 92, and 93 of the first current mirror circuit 94 are commonly connected to a power supply 90, and the bases are commonly connected to each other. The transistor 91 has a base and a collector connected to each other, and the collector is grounded via a constant current source 99.

The collectors of the transistors 92 and 93 are
The transistors 95 and 96 are connected to the respective collectors. The transistor 95 has a collector and a base connected to each other. The bases of the transistors 95 and 96 are connected to each other, and the emitters are grounded. The collector of transistor 96 is grounded via capacitor 98.

The reference voltage switching circuit 82 includes three resistors 101, 10 connected in series between the power supply 100 and the ground.
2 and 103, and an NPN transistor 104 that operates in response to the clock of the frequency dividing circuit 62. The transistor 104 has a collector connected to the resistor 102 and the resistor 10.
3 and the emitter is grounded. Minute
The clock A whose frequency is divided by ４ in the frequency divider 62 is supplied to the base of the transistor 104.

The non-inverting input terminal of the first comparator 83 is connected to a connection point C between the capacitor 98 and the transistor 96, while the inverting input terminal is connected to a connection point B between the resistors 101 and 102. . The inverting input terminal of the second comparator 84 is connected to the connection point C, while the non-inverting input terminal is connected to the reference power supply 105.

The outputs D and E of the first and second comparators 83 and 84 are supplied to a set input terminal and a reset input terminal of the flip-flop 85, respectively. The Q output of flip-flop 85 is applied to the bases of transistors 95 and 96.

When the Q output is set to the L level, the transistor 96 is turned off, the constant current I flowing through the transistor 93 flows into the capacitor 98, charging is started, and the potential at the connection point C rises. On the other hand, when the Q output is set to the open state, the transistor 96 is turned on, the connection point C is grounded via the transistor 96, the capacitor 98 starts discharging, and the voltage at the connection point C drops. In this way, the Q output allows the capacitor 9
8 repeats charging and discharging, and a triangular wave voltage is generated at the connection point C.

Next, referring to FIG.
1 will be described. The reference clock (3.58 MHz) from the oscillator 60 is frequency-divided by 1/4 in the frequency dividing circuit 62, and the frequency-divided clock A (895 kHz) shown in FIG.
z), which is provided to transistor 104.

For example, in the period T0 from time t0 to t1, the divided clock A is at the H level, so that the transistor 104 is turned on and the connection point G is grounded. Therefore, the connection point B sets the power supply voltage Vcc of the power supply 100 to 2
A voltage divided by the two resistors 101 and 102 (hereinafter, referred to as a first voltage V1) is set.

On the other hand, for example, a period T between times t1 and t2
In 1, the divided clock A is at the L level, so that the transistor 104 is turned off, and the ground state of the connection point G is released. Therefore, the connection point B connects the power supply voltage Vcc of the power supply 100 to the resistor 101 and the two resistors 102 and 1 to each other.
The voltage is set to the voltage divided at 03 (hereinafter, referred to as a second voltage V2). Hereinafter, similarly, the voltage at the connection point B is set by alternately repeating the first voltage V1 and the second voltage V2 in synchronization with the divided clock A.

When the first voltage V1 is set in the range of Vref <V1 <V2 (1), a stable triangular wave can be obtained. Actually, as the voltage approaches the second voltage V2, the control range of the external synchronization becomes narrower.
It is desirable to set a voltage in the middle of the range of the expression, that is, V1 = (Vref + V2) / 2 (2).

The first voltage V1 is set lower than the upper limit voltage Vmax of the triangular wave voltage described later, and the second voltage V2 is set higher than the upper limit voltage Vmax of the triangular wave voltage. On the other hand, the reference voltage Vref set by the reference voltage 105 is a lower limit voltage Vmi of a triangular wave voltage described later.
n.

Here, taking into account the above equation (1), the relationship between these voltages is summarized as follows: Vref−Vmin <V1 <Vmax <V2 (3)

Specifically, for example, assuming that the upper limit voltage Vmax of the triangular wave voltage is 1.8 V and the minimum voltage Vmin is 1.0 V, the power supply voltage Vcc of the power supply 100 is 2.5 V, and the resistances of the resistors 101, 102, and 103 are different. The resistance value is 5 kΩ each,
By setting 7.5 kΩ and 12.5 kΩ, the first voltage V1 =
1.5V and the second voltage V2 = 2.0V. The reference voltage Vref is set to 1.0V.

Here, the case where the waveform of (6) in FIG. 4 is obtained as the Q output of the flip-flop 85 will be described. For example, in a period T1 between times t1 and t2,
Since the Q output is at the L level, the transistor 96 is turned off, the capacitor 98 is charged with the constant current I, and the voltage at the node C rises to the upper limit voltage Vmax.
At this time, since the second voltage V2 that is higher than the upper limit voltage Vmax of the triangular wave voltage is set in the reference voltage switching circuit 82, the voltage at the connection point C does not become higher than the voltage at the connection point B. Therefore, in the period T1, the output D of the first comparator 83 is at the L level.

When the Q output changes from the L level to the open state at time t2, the capacitor 98 starts discharging, and the voltage at the node C starts to drop. On the other hand, in the period T2 from the time t2 to the time t3, as described above, the connection point B is set to the first voltage V1 smaller than the maximum voltage Vmax of the triangular wave voltage . Voltage
In the period Ta until the voltage drops to V1, the voltage at the connection point C becomes higher than that at the connection point B. Therefore, this period T
In a, the output D of the first comparator 83 is in an open state as shown in (4) of FIG.

In a period T2 between times t2 and t3, the capacitor 98 is discharging and the voltage at the node C is changed to the time t2.
3, the voltage drops to the lower limit voltage Vmin. Meanwhile, the standard
Since the reference voltage Vref set by the power supply 105 is set to the lower limit voltage Vmin as described above, the output E of the second comparator 84 becomes instantaneous as shown in (5) of FIG. Stand up.

When the outputs D and E are given as the set and reset inputs of the flip-flop 85, respectively, the Q output has the waveform shown in (6) of FIG. Given, connection point C is
(3), a triangular wave voltage C whose amplitude falls between a certain upper limit voltage Vmax and a lower limit voltage Vmin is obtained.

When the switching timing of the reference voltage in the reference voltage switching circuit 82 is synchronized with the divided clock A in this manner, the oscillation cycle of the triangular wave voltage C is also changed by the divided clock A.
Will be synchronized. Therefore, the triangular wave oscillation circuit 5
1, the switching transistor 54a responding to the output of
The switching operation of 54b is also synchronized with the frequency-divided clock, so that noise that cannot be eliminated by the smoothing circuits 55a and 55b and beat noise due to the asynchronization of the reference clock can be removed. As a result, it is possible to eliminate defects such as screen disturbance caused by beat noise, and to improve the characteristics of the VTR.

The triangular wave oscillating circuit 51 outputs a symmetrical triangular wave voltage as an output voltage, so that there is an advantage that high frequency noise is less than that of a sawtooth wave at the same frequency and the same amplitude.

[0050]

According to the present invention as described above, claim 1
Then, the second signal forming the set signal of the flip-flop is
Switch the reference voltage of the comparator, and
Switching timing is synchronized with an external clock
Therefore, the oscillation cycle of the triangular wave voltage can be easily and reliably set to an external clock.
You can actually synchronize. Furthermore, for the clock
A second ratio to which a synchronously switched reference voltage is input
The output of the comparator to the set terminal of the flip-flop,
And inputting the output of the first comparator to the reset terminal
Using the output of the flip-flop
Controls charging / discharging of the capacitor.
It is possible to perform a triangular wave oscillation with a stable and stable amplitude.

According to a second aspect of the present invention, the switching means includes a first resistor having one end connected to a power supply and a second resistor having one end grounded.
, A third resistor connected to the other end of the first resistor and the other end of the second resistor, and an output voltage from a connection point between the first resistor and the third resistor. and means, connected to the collector terminal to the connection point of the second resistor and the third resistor, the emitter comprises a substantially grounded switching transistor, oN in response to the clock signal of the transistor from the outside Since the / OFF control is performed, there is an effect that synchronization with an external clock can be obtained and triangular wave oscillation with stable amplitude can be performed.

According to the third aspect, the output voltage of the switching means when the switching transistor is turned on is set higher than the reference level of the first comparator. Since one comparator does not operate, there is an effect that synchronization with an external clock can be obtained and triangular wave oscillation with stable amplitude can be performed.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of a VTR using a triangular wave oscillation circuit according to an embodiment of the present invention.

FIG. 2 is a waveform chart showing an operation of a main part in the embodiment.

FIG. 3 is a block diagram illustrating a configuration of a triangular wave oscillation circuit according to the same embodiment.

FIG. 4 is a waveform chart showing an operation of a main part of the triangular wave oscillation circuit in the embodiment.

FIG. 5 is a block diagram illustrating a typical prior art configuration.

FIG. 6 is a block diagram showing a configuration of a triangular wave oscillation circuit in the prior art.

[Explanation of symbols]

 Reference Signs List 40 power supply circuit 41 video signal processing circuit 42 monitor control circuit 51 triangular wave oscillation circuit 53a, 53b pulse width control circuit 54a, 54b switching transistor 55a, 55b smoothing circuit 56a, 56b, 57a, 57b comparator 60 oscillator 61 frequency dividing circuit 81 filling Discharge circuit 82 Reference voltage switching circuit 83, 84 Comparator 85 Flip-flop

Claims (4)

(57) [Claims] 1. A capacitor, a current source for charging / discharging the capacitor, a first comparator for comparing a voltage output of the capacitor with a predetermined reference level, and a reference voltage synchronized with an external clock signal. The reference level
Switching means for alternately switching and outputting a first voltage and a second voltage different from the first voltage, a second comparator for comparing an output of the switching means with an output voltage of the capacitor, and an output of the second comparator. And a flip-flop for connecting the output of the first comparator to the reset terminal, and controlling the charging and discharging of the capacitor by the current source according to the output of the flip-flop. A triangular wave oscillation circuit. 2. The switching means includes: a first resistor having one end connected to a power supply; a second resistor having one end grounded; and a second resistor having the other end of the first resistor and the second resistor. A third resistor connected to an end, means for extracting an output voltage from a connection point between the first resistor and the third resistor, and a collector terminal connected to a connection point between the second resistor and the third resistor. Connected, the emitter is substantially grounded , and
Switch that is ON / OFF controlled according to the clock signal
The triangular wave oscillation circuit according to claim 1, further comprising: a switching transistor . 3. The triangular wave oscillation circuit according to claim 2, wherein an output voltage of said switching means when said switching transistor is turned on is set higher than said reference level of said first comparator. . 4. A video signal processing apparatus comprising the triangular wave oscillation circuit according to claim 1 , wherein an output of the triangular wave oscillation circuit is synchronized with a reference oscillation source for processing a video signal. .