JP3300514B2 - Peak clipping circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a peak clipping circuit formed on an integrated circuit for a high-frequency modulator for generating a television signal used in, for example, a video tape recorder, and more particularly to a peak clipping circuit using a voltage comparison circuit. About.

[0002]

2. Description of the Related Art A conventional peak clipping circuit of this kind is
A voltage comparison circuit as shown in FIG. 5 has been used. This voltage comparison circuit includes a PNP transistor P1, which forms a differential pair in which an input signal Vin and a reference voltage Vref are input to each base.
P2 and a constant current source circuit 50 commonly connected to each emitter of the differential pair transistor, and performs peak clipping of the input signal Vin by utilizing the switching characteristics of the differential pair transistor.

However, the input / output characteristics of such a conventional peak clipping circuit are, as shown in FIG.
, The clipping operation starts gradually before reaching the clip point and the clipping characteristic (voltage change characteristic near the clipping voltage) is gentle. Also, the output voltage V
The level of out is shifted higher by the emitter-base voltage VEB of the PNP transistors P1 and P2.

Japanese Patent Application Laid-Open No. 1-49308 discloses a technique for improving the linearity of an input / output voltage near a clip voltage. Japanese Patent Application Laid-Open No. 61-125220 discloses a technique of obtaining a transfer characteristic with good linearity by applying positive feedback to a differential amplifier.

[0005]

As described above, the conventional peak clipping circuit including only the voltage comparison circuit has a problem that the clipping characteristic is moderate. SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a peak clipping circuit capable of sharpening clip characteristics and improving high frequency characteristics.

[0006]

A peak clipping circuit according to the present invention is a positive feedback type voltage comparing circuit for comparing a voltage between an input signal and a reference voltage, and is controlled by a comparison output of the voltage comparing circuit. And a switch circuit for selectively selecting and outputting the input signal or the reference voltage in response to clipping, and the positive feedback voltage comparison circuit.
The input signal is input to the base and the collector is
A first NPN transistor connected to the
One end is connected to the emitter of one NPN transistor
A first level shift element, and the first level shift element
A first constant current source circuit connected to the other end of the
A first level shift circuit for level shifting the input signal;
And the reference voltage are input to the base, and the collector is the power supply potential.
A second NPN transistor connected to the node;
One end is connected to the emitter of the second NPN transistor
A second level shift element, and the second level shift element
A second constant current source circuit connected to the other end of the element.
And a second level shifter for shifting the level of the reference voltage.
Circuit, and the base is the other end of the first level shift element.
And the collector is connected to the second level shift element.
A third NPN transistor connected to one end and a base
Is connected to the other end of the second level shift element.
Is connected to one end of the first level shift element,
The emitter is the emitter of the third NPN transistor
Commonly connected to the third NPN transistor
A fourth NPN transistor forming a differential pair with the third
And the common emitter of the fourth NPN transistor
And a third constant current source circuit .

[0007]

The voltage comparison between the input signal and the reference voltage is rapidly performed by the positive feedback type voltage comparison circuit, and the switching circuit is switched and selected by the rapidly changing voltage comparison output to select the input signal (when the signal is not clipped). ) Or reference voltage (when clipping)
Is output, so that the clip characteristics can be sharpened.

If the voltage comparison circuit of the positive feedback type is configured to compare only the NPN transistor without using the lateral PNP transistor, an overshoot at a clip point due to a delay in response to an input signal may occur. No longer occurs, improving high-frequency characteristics,
Good clip characteristics are obtained.

[0009]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a block configuration of a peak clipping circuit according to one embodiment of the present invention.

This peak clipping circuit uses an input signal Vin
And a reference voltage Vref. A positive feedback type voltage comparison circuit 11 for comparing the voltage of the input signal Vin or the reference voltage Vref. And a switch circuit 12 for selecting and outputting Vref.

This peak clipping circuit is formed in, for example, an integrated circuit for a high-frequency modulator for a video tape recorder, and generates a television signal by amplitude-modulating a carrier signal of several hundred MHz using, for example, an NTSC television composite video signal. Before it is used to limit the amplitude of the composite video signal.

According to the above-mentioned peak clipping circuit, the voltage comparison between the input signal Vin and the reference voltage Vref is rapidly performed by the positive feedback type voltage comparing circuit 11, and the switching circuit is provided by the rapidly changing voltage comparison output. 12 is switched and selected, the input signal Vin is output when not clipping, and the reference voltage Vref is output when clipping, so that the clip characteristics can be made more agile.

FIG. 2 shows the input / output characteristics of the peak clipping circuit of FIG. 1, and the clipping characteristics have become more abrupt as compared with the input / output characteristics of the conventional peak clipping circuit as shown in FIG. It can be seen that the level shift of the output voltage Vout has not occurred.

FIG. 3 is a circuit diagram showing a specific example of the peak clipping circuit of FIG. In FIG. 3, a positive feedback type voltage comparison circuit 11 has a first N-type input signal Vin input to a base and a collector connected to a power supply potential (VCC) node.
A first level shift circuit 31 for level shifting the input signal Vin using a PN transistor N1, and a reference voltage source 3
The reference voltage Vref input from 0 is input to the base, and the collector is level-shifted using the second NPN transistor N2 connected to the VCC node.
, And an input signal level-shifted by the first level shift circuit 31 and a reference voltage level-shifted by the second level shift circuit 32 are input corresponding to each base. A third NPN transistor N3 and a fourth NPN transistor forming a differential pair whose emitters are connected in common and whose collectors are correspondingly connected to the second level shift circuit 32 and the first level shift circuit 31, respectively. N4 and a first constant current source circuit 41 commonly connected to the emitters of the differential pair transistors N3 and N4.

The first level shift circuit 31 is provided between the first NPN transistor N1 and the emitter of the first NPN transistor N1 and the base of the third NPN transistor N3 in a forward direction. It comprises a first diode D1 for level shift inserted, and a second constant current source circuit 42 connected between the cathode of the first diode D1 and ground potential (GND).

The second level shift circuit 32
Are the second NPN transistor N2, the emitter of the second NPN transistor N2 and the fourth NPN transistor N2.
A second diode D2 for level shift inserted in the forward direction between the base of the transistor N4 and a third constant current source connected between the cathode of the second diode D2 and GND. And a circuit 43.

The first NPN transistor N
The collector of the fourth NPN transistor N4 is connected to the emitter of the second NPN transistor N2.
Is connected to the collector of the third NPN transistor N3.

On the other hand, the switch circuit 12 comprises a switch circuit section 21 and a voltage follower section 22.
The switch circuit section 21 receives a differential pair in which the base potential of the fourth NPN transistor N4 and the base potential of the third NPN transistor N3 are input to the respective bases and the respective emitters are connected in common. Fifth NPN
Transistor N5 and sixth NPN transistor N6
And a fourth constant current source circuit 44 commonly connected to the emitters of the differential pair transistors N5 and N6.

The voltage follower section 22 includes:
The input signal Vin is input to the base, and the Vcc node and the fifth
NPN transistor N having a collector and an emitter connected between the collector and the collector of NPN transistor N5.
7, an eighth NPN transistor N8 having an emitter commonly connected to the emitter of the seventh NPN transistor N7, a VCC node and the eighth NPN transistor N7.
Fifth constant current source circuit 4 connected between
5, a reference voltage Vref is input to the base, a ninth NPN transistor N9 having a collector-emitter connected between the Vcc node and the collector of the sixth NPN transistor N6, and an emitter connected to the ninth NPN transistor N9. A tenth NPN transistor N10 having a collector commonly connected to the emitter of the NPN transistor N9 and a collector commonly connected to the collector of the eighth NPN transistor N8, a collector connected to the VCC node, and a base connected to the eighth NPN transistor N9; NPN transistor N8 and tenth NPN transistor N10
An eleventh NPN transistor N11 whose emitter (switch circuit output node) is connected to each base of the eighth NPN transistor N8 and the tenth NPN transistor N10.
The emitter of the eleventh NPN transistor N11 and G
And a sixth constant current source circuit 46 connected to the ND.

Next, the operation of the peak clipping circuit shown in FIG. 3 will be described. Now, the level relationship between Vin and Vref is Vin >> V
ref or Vin << Vref, the transistor N
3 and N4, the entire current I1 of the first constant current source circuit 41 flows, and even if Vin changes, the transistor N3,
Each collector current of N4 does not change.

On the other hand, when the level of Vin rises so as to approach Vref and approaches Vin = Vref, the collector current IC3 of the transistor N3 increases and the collector current IC4 of the transistor N4 decreases. Here, since the collector of the transistor N4 is connected to the emitter of the transistor N1 of the first level shift circuit 31, which is the input stage of the transistor N3, the collector current IC4
Is represented by ΔIC4, the variation ΔIE1 of the emitter current IE1 of the transistor N1 is ΔIE1 = −ΔIC4. That is, the change ΔIE1 in the emitter current of the transistor N1 decreases, and the base-emitter voltage VBE
N1 decreases.

Thus, the change (decrease) in VBEN1 is added to the change (increase) in Vin for the change in the base potential of the transistor N3, and positive feedback is applied to the voltage comparison operation. = Vref, the voltage comparison operation is performed rapidly.

Similarly to the above, when the level of Vin falls so as to approach Vref and approaches Vin = Vref, the collector current IC3 of the transistor N3 decreases and the collector current IC4 of the transistor N4 increases. When the increase in the collector current IC4 is represented by ΔIC4, the transistor N1
Of the emitter current of the transistor N1 becomes ΔIE1 = + ΔIC4, and the change ΔI1 of the emitter current of the transistor N1 is ΔI1.
E1 increases, and its base-emitter voltage VBEN1 increases.

Thus, the change in the base potential of the transistor N3 is equal to the change (decrease) in the Vin.
The change (increase) of BEN1 is added, positive feedback is applied to the voltage comparison operation, and the voltage comparison operation is rapidly performed.

In the above operation, the diode D1
Has a function of shifting the level of the input signal by the forward voltage drop and preventing the operation of the transistor N4 from being saturated, and the diode D2 performs the level shift of the reference voltage by the forward voltage drop. It has an effect of preventing saturation of the operation of the transistor N3.

On the other hand, for example, in the region of Vin <Vref, the base potential VB3 of the transistor N3 is changed to the transistor N3.
4 (VB3 <VB4), the transistor N5 is turned on in the switch circuit section 21,
The transistor N6 is turned off.

As a result, in the voltage follower unit 22, the transistors N7, N8 and N11 using the transistor N5 as a current source, the fifth constant current source circuit 45, and the sixth constant current source circuit 46 are formed. The voltage follower circuit operates. in this case,
A transistor N using the transistor N6 as a current source
9, N10 is off, and the fifth constant current source circuit 45
Of the current I3 of the fourth constant current source circuit 44 is 1 /
If it is set to be 2, the base potentials of the transistors N7 and N8 are made equal, and the level of the output signal Vout of the voltage follower unit 22 becomes equal to Vin.

On the contrary, in the region of Vin> Vref,
Since the base potential VB3 of the transistor N3 is higher than the base potential VB4 of the transistor N4 (VB3> VB4), in the switch circuit section 21, the transistor N5 is turned off and the transistor N6 is turned on.

As a result, in the voltage follower section 22, the transistors N7 and N8, which use the transistor N5 as a current source, are off, and the transistor N5 is turned off.
The voltage follower circuit formed by the transistors N9, N10 and N11, the fifth constant current source circuit 45, and the sixth constant current source circuit 46 using 6 as a current source operates. In this case, the current I4 of the fifth constant current source circuit 45 is １ ／ of the current I3 of the fourth constant current source circuit 44.
Therefore, the base potentials of the transistors N9 and N10 are equalized, and the output signal Vou of the voltage follower unit 22 is set.
The level of t will be equal to Vref.

According to the peak clipping circuit shown in FIG. 3 as described above, the positive feedback type voltage comparison circuit does not use a lateral PNP transistor whose high frequency characteristics are relatively poor due to an integrated circuit manufacturing process. Level shift and voltage comparison are performed using only NPN transistors having relatively good characteristics. As a result, there is no response delay to the input signal Vin in the high frequency region (for example, a 3.58 MHz chroma signal included in the NTSC television composite video signal), and overshoot at the clip point due to the response delay does not occur. The high-frequency characteristics can be improved, and good clip characteristics can be obtained as shown by the solid line in FIG.

The dotted line in FIG. 4 shows an overshoot characteristic generated when a chroma signal is clipped by a conventional peak clipping circuit for comparison.
It should be noted that the present invention is not limited to the above-described embodiment, and a specific circuit corresponding to the block configuration of FIG. 1 can have various configurations, and the peak clipping for various input signals other than the television composite video signal is possible. Operation is possible.

[0032]

As described above, according to the peak clipping circuit of the present invention, the clipping characteristics can be sharpened and the high frequency characteristics can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a peak clipping circuit according to one embodiment of the present invention.

FIG. 2 is a diagram showing input / output characteristics of the peak clip circuit of FIG. 1;

FIG. 3 is a circuit diagram showing a specific example of the peak clip circuit of FIG. 1;

FIG. 4 is a view showing clip characteristics for a chroma signal by the peak clip circuit of FIG. 3 and a clip characteristic of a conventional example.

FIG. 5 is a circuit diagram showing an example of a conventional peak clip circuit.

FIG. 6 is a diagram showing input / output characteristics of the peak clip circuit of FIG. 5;

[Explanation of symbols]

11: positive feedback type voltage comparison circuit, 12: switch circuit,
21: switch circuit unit, 22: voltage follower unit,
Reference numeral 30: reference voltage source, 31: first level shift circuit, 3
2 second level shift circuit, 41 to 46 constant current source circuit, N1 to N11 NPN transistor, D1, D2
diode.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-61-125220 (JP, A) JP-A-6-177687 (JP, A) Real-life 1987-127114 (JP, U) (58) Survey Field (Int.Cl. ⁷ , DB name) H03G 11/00 H04N 5/20

Claims (2)

(57) [Claims] A positive feedback type voltage comparing circuit for comparing a voltage between an input signal and a reference voltage, controlled by a comparison output of the voltage comparing circuit, wherein the input signal or ingredients and a switch circuit for selecting and outputting switching the reference voltage
In the positive feedback type voltage comparison circuit, an input signal is input to a base, and a collector is connected to a power supply potential node.
A first NPN transistor connected to the first
A first terminal having one end connected to the emitter of the NPN transistor;
And the first level shift element
And a first constant current source circuit connected to the other end.
First level shift circuit for level shifting an input signal
And the reference voltage is input to the base, and the collector is the power supply potential node.
A second NPN transistor connected to the second
A second terminal having one end connected to the emitter of the NPN transistor;
And the second level shift element
And a second constant current source circuit connected to the other end.
Second level shift circuit for level shifting reference voltage
And a base connected to the other end of the first level shift element.
And a collector is connected to one end of the second level shift element.
A third NPN transistor connected to the second level shift element and a base connected to the other end of the second level shift element;
And a collector is connected to one end of the first level shift element.
The emitter is the emitter of the third NPN transistor.
The third NPN transistor commonly connected to the
A fourth NPN transistor that forms a differential pair with the third NPN transistor, and a common emitter of the third and fourth NPN transistors.
Peak clipping circuit, characterized in that it is constituted by a third constant current source circuit connected to the motor. 2. The peak clipping circuit according to claim 1 , wherein said switch circuit comprises a second level and a first level of said second and first level shift circuits .
The fifth and sixth NPNs form a differential pair in which the voltage at the other end of the shift element is input to each base and the emitters are connected in common.
A transistor; a fourth constant current source circuit connected to a common emitter of the fifth and sixth NPN transistors; an output terminal for outputting a peak-clipped signal; an input signal input to a base; Is connected to the power supply potential node, and the emitter is the fifth NPN transistor.
A seventh NPN transistor connected to the collector of the above, a signal of the output terminal is input to a base, and an emitter is
Eighth transistor connected to the collector of the fifth NPN transistor
A reference voltage is input to the base, a collector is connected to the power supply potential node, and an emitter is the sixth NPN transistor.
A ninth NPN transistor connected to the collector of the above, a signal of the output terminal is input to a base, and an emitter is
The first connected to the collector of the sixth NPN transistor
0 and NPN transistor, and the eighth and tenth fifth constant-current source circuit connected in common to the collectors of the transistors of the base of the common collector of the fifth transistor of the eighth and tenth An eleventh NPN transistor connected to a connection point with the constant current source circuit, a collector connected to the power supply potential node, and an emitter connected to the output terminal; a sixth constant current source connected to the output terminal A peak clipping circuit comprising: