JP3316357B2 - Clip detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a clip detection circuit suitable for use in a BTL-driven amplifier having a fixed output bias.

[0002]

2. Description of the Related Art Generally, when an output signal level of an amplifier exceeds a dynamic range of the amplifier,
The output signal of the amplifier is clipped, and the distortion factor deteriorates. Therefore, conventionally, a clip detection circuit for detecting that the output signal of the amplifier has been clipped is provided, and the input signal level of the amplifier is reduced according to the output signal of the clip detection circuit at the time of clip detection, whereby the output signal of the amplifier is reduced. To prevent clipping. A circuit as shown in FIG. 2 is known as a clip detecting circuit for detecting such a clip of the output signal of the amplifier.

In FIG. 2, an input signal is supplied to an amplifier (1).
Output signals which are amplified in a) and (1b) and have the same level in opposite phases to each other are applied from the amplifier (1) to both ends of the speaker (2). Therefore, the amplifiers (1a) and (1)
According to the output signal of b), the loudspeaker (2) is in BTL (B
(Alternated Transformerless) drive. When the output signals of the amplifiers (1a) and (1b) are not clipped, the transistors (3) and (4) are turned on, and the transistors (5) and (6) are also turned on. When the transistors (5) and (6) are turned on, the connection point between the resistors (7) and (8) is grounded. Therefore, the transistor (9) is turned off,
An "H" level output signal indicating that the output signal from the output terminal (10) is not clipped is generated.

Here, when a clip occurs in the output signal (a) of the amplifier (1), the level of the output signal (a) from the amplifier (1) becomes substantially equal to the power supply voltage Vcc. The base voltage of 3) approaches its emitter voltage and transistor (3) turns off. When the transistor (3) is turned off, the base of the transistor (5) is grounded, and the transistor (5) is also turned off. When the transistor (5) is turned off, the midpoint output voltage of the resistors (7) and (8) is applied to the transistor (9), so that the transistor (9) is turned on and the output terminal (1)
0) generates an “L” level signal. When a clip occurs in the output signal (b) of the amplifier (1),
When the transistor (4) is turned off, the transistor (6) is also turned off, which further turns on the transistor (9), so that an output signal of "L" level is generated from the output terminal (10). Therefore, when a clip occurs, the output signal changes from the output terminal (10).
Using this output signal, a clip can be detected.

[0005]

In some amplifiers, the output DC voltage of the amplifier is reduced to 1/2 of the power supply voltage Vcc.
There is an amplifier that drives the load with a half-wave output signal at the following voltage, but in such an amplifier, the output DC voltage is set to Vcc / 2 or less and the load is driven by the half-wave signal. The negative half cycle side of the signal is shown in FIG.
Clipped as indicated by the solid line in (a). Therefore, the clip detection circuit of FIG. 2 can detect a clip only on the high level side of the output signal of the amplifier (1). Since the clip detection circuit shown in FIG. 2 is an amplifier that generates a half-wave output signal, accurate clip detection cannot be performed unless a clip is detected on the high level side and the low level side of the output signal. However, the clip detection circuit shown in FIG.

Further, since the clip detection circuit shown in FIG. 2 is directly connected to the load, there is a problem that the voltage across the load changes according to the resistance value of the load, and clip detection is erroneously performed. That is, when the amplifier (1) amplifies an input signal of a predetermined level, the amplifier (1) clips when a load having a first value is connected to the output terminal of the amplifier (1).
Is the first output level, the second output level of the amplifier (1) that clips when a second load having a second value smaller than the first load is connected is lower than the first output level. Become. In FIG. 2, the output level of the amplifier (1) is viewed with respect to a fixed clip detection level, and the clip is detected with the first load, but the clip may not be detected with the second load. However, there has been a problem that it is not possible to perform an accurate clip detection.

Further, if the clip detection level is changed according to the load, the clip can be detected accurately. The change of the clip detection level is performed by, for example, the resistors (11) and (12).
However, the adjustment is difficult because the value of the resistor (8) and the saturation level of the output transistor included in the amplifier (1) must be taken into consideration.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and includes two input terminals, two output terminals, and a control terminal for determining a DC level of the output terminal.
An amplifier that amplifies an input signal from one input terminal, generates an output signal of the same level in opposite phase to each other, and BTL-drives the load; and, when one output signal level of the amplifier is equal to or higher than a predetermined value, An amplification device comprising: a nonlinear addition circuit that clamps the other output signal of the amplifier to a predetermined level; and a comparison circuit that applies an output signal corresponding to a difference between an output signal of the nonlinear addition circuit and a reference voltage to the control terminal. A clip detecting circuit for detecting a clip by detecting that an output signal of the non-linear adding circuit has become equal to or more than a predetermined value from the reference voltage or equal to or less than a predetermined value.

The detection section is also used as a non-linear addition circuit. The first transistor has a base to which an input signal is applied, a bias is applied to the base, and the emitter is commonly connected to the emitter of the first transistor. A second transistor, and an output stage circuit for generating an output signal indicating whether or not clipping has been detected in accordance with an output signal generated from the collector of the first transistor.
An output signal is generated from a collector of the transistor to a control terminal of the amplifier.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing an embodiment of the present invention. (12) is an amplifier circuit (12) having a control terminal.
an amplifier including a) and (12b) and an inverting circuit (12c); (13) a first input resistor to which an input signal is applied;
(14) is a first feedback resistor for negatively feeding back an output signal from the positive output terminal of the amplifier (12), (15) is a second input resistor to which a bias is applied, and (16) is an amplifier (12).
A second feedback resistor for negatively feeding back the output signal from the negative output terminal of (1), (17) a load, (18) an amplifier (12)
First and second summing resistors (19) and (20) connected between the positive and negative output terminals of the amplifier, and diodes (21) and (21) whose cathodes are connected to the positive and negative input terminals of the amplifier (12), respectively. 22), and (2)
3) is a comparison circuit for comparing an output signal of the nonlinear addition circuit (18) with a reference voltage, and (24) is a nonlinear addition circuit (18).
Is a clip detection circuit that detects a clip according to the output signal of the clip detection circuit, and (25) is a level variable circuit that varies the level of the input signal according to the output signal of the clip detection circuit (24). For the sake of simplicity, the control terminals of the amplifier circuits (12) and (13) will be referred to as control terminals of the amplifier (12).

In FIG. 1, an input signal is amplified by an amplifier circuit (12a) via a first input resistor (13), inverted by an inverter circuit (12c), and then amplified by an amplifier circuit (12b). An output signal generated from an output terminal of the amplifier (12) is supplied to a load (17). Since the output signals are signals having opposite phases and the same level, the load (17) is BTL-driven by the output signal of the amplifier (12). Output signals generated from the positive and negative output terminals of the amplifier (12) are fed back to the negative and positive input terminals, respectively.

In the non-linear addition circuit (18), two output signals of the amplifier (12) are added, and the output signal of the non-linear addition circuit (18) is compared with a reference voltage in a comparison circuit (23). Then, a comparison circuit (23) according to the comparison result
Is applied to the control terminal of the amplifier (12), and the output DC voltage of the amplifier (12) is controlled according to the output signal of the comparison circuit (23). Since the loop from the output terminal of the amplifier (12) to the control terminal of the amplifier (12) via the nonlinear addition circuit (18) and the comparison circuit (23) forms a negative feedback loop, the loop of the amplifier (12) is positive. And the output DC level generated from the negative output terminal is kept constant.

In the nonlinear adder circuit (18), when the two output signals of the amplifier (12) are lower than the forward voltages of the diodes (21) and (22), the diode (2)
1) and (22) become non-conductive. Therefore, the two output signals of the amplifier (12) are applied to the load (17) as shown in FIG.
Are applied in a waveform as shown by a solid line and a dotted line, respectively. FIG.
Since the output signals of the amplifier circuits (12a) and (12b) as shown in (a) are negatively fed back, the amplifier circuit (12a)
The gain of the first input resistor (13) and the first feedback resistor (1)
If the resistance values of 4) are R1 and R2, respectively, then １ ／
× R2 / R1, and the gain of the amplifier circuit (12b) is ×× R4 / R3 if the resistance values of the second input resistor (15) and the second feedback resistor (16) are R3 and R4, respectively.
Becomes Therefore, the gain of the amplifier (12) as a whole is R
It operates as a 2 / R1 linear amplifier. The signal flowing to the load (17) is as shown in FIG. Also,
The output signals of the amplifier (12) are added by the addition resistors (19) and (20), and the signals are output from the nonlinear addition circuit (18) to FIG.
A signal having a substantially constant level as shown in (c) is generated. An output signal of the non-linear addition circuit (18) is compared with a reference voltage in a comparison circuit (23), and a control signal corresponding to a difference between the output signal and the reference voltage is applied to a control terminal of the amplifier (12).
On the other hand, the output signal of the non-linear addition circuit (18) is applied to the clip detection circuit (24). Clip detection circuit (2
4) Detects a clip when the output signal level of the non-linear addition circuit (18) changes to a certain level or more. Therefore, during the steady operation, the clip is not detected because the output signal level of the nonlinear addition circuit (18) is substantially constant. Therefore, no output signal is generated from the clip detection circuit (24), and the input signal level is changed to the level variable circuit (2).
It is applied to the amplifier (12) without lowering in 5).

When the amplitude of the input signal increases, for example,
When the output signal of the amplifier circuit (12a) becomes higher than the output DC voltage by the forward voltage of the diode (21), the diode (21) is in a non-conductive state, and the output signal of the positive output terminal is directly output as the positive output. It is supplied to the terminal. Also,
Since the output signal of the amplifier circuit (12b) is lower than the output DC voltage by the forward voltage of the diode (22) and the diode (22) becomes conductive, the amplifier circuit (12b)
Is clamped to a substantially constant level. To be precise, the output signal of the negative output terminal is a signal obtained by compressing the input signal to be approximately proportional to the logarithm of the output DC voltage due to the VI characteristic of the diode. Further, since the diode (21) is in a non-conductive state, the amplifier circuit (12
The gain of a) is R2 / R1, and the output signal of the amplifier circuit (12a) having the gain is supplied to the load (17).

Conversely, when the output signal of the amplifier circuit (12b) is higher than the output DC voltage by the forward voltage of the diode (22), the output signal of the amplifier circuit (12a) is lower than the DC output voltage by the diode (12). Since the voltage becomes lower than the forward voltage of 21), the diode (21) becomes conductive and the output signal level of the amplifier circuit (12a) is clamped at a constant level. Further, since the diode (22) is in a non-conductive state, an output signal amplified with a gain of R4 / R3 is obtained at an output terminal of the amplifier circuit (12b) and supplied to the load (17).

Therefore, according to the output signal level of the amplifier (12), the diode (2) of the nonlinear addition circuit (18)
The waveforms of the two output signals of the amplifier (12) are changed as shown in FIG.
The solid line and the dotted line in FIG. And the load (1
The signal flowing in 7) is as shown in FIG. 3B, and an accurate sine wave signal is obtained, so that no crossover distortion occurs.

Here, the output signal of the non-linear addition circuit (18) will be described. When the input signal is a small signal, since the diodes (21) and (22) are not conducting, the two output signals of the amplifier (12) are respectively shown in FIG.
It becomes a signal obtained by directly amplifying the input signal as shown by the solid line and the dotted line in (a). Therefore, the signal flowing to the load (17) is as shown in FIG. Further, since the diodes (21) and (22) are in a non-conductive state, the output signals of the amplifier (12) are added by the addition resistors (19) and (20), and the signals are output from the non-linear addition circuit (18) to FIG. A signal having a substantially constant level is generated. An output signal of the non-linear addition circuit (18) is compared with a reference voltage by a comparison circuit (23), and a control signal corresponding to a difference between the output signal and the reference voltage is supplied to the amplifier (1).
2) is applied to the control terminal. On the other hand, the output signal of the non-linear addition circuit (18) is applied to the clip detection circuit (24). Since the output signal level of the nonlinear addition circuit (18) is substantially constant, no output signal is generated from the clip detection circuit (24), that is, no clip is detected. Since no output signal is generated from the clip detection circuit (24),
The input signal level is not reduced by the level variable circuit (25). The input signal is applied to the amplifier (12) at the same level.

When the input signal is a medium signal, one of the diodes (21) and (22) is turned off or the other is turned on.
The two output signals are signals as shown by a solid line and a dotted line in FIG. Therefore, the signal flowing to the load (17) is as shown in FIG. 3B and has a waveform obtained by amplifying the input signal. In addition, the nonlinear addition circuit (1
The output signal of 8) adds the two output signals of the amplifier (12) when both output signal levels of the amplifier (12) are lower than the output DC voltage by the forward voltage of the diode.
When the output signal of 2) is higher than the output DC voltage by the forward voltage, the diode is clamped, and thus becomes substantially constant. Then, a signal corresponding to the difference between the reference voltage and the output signal of the nonlinear addition circuit (18) is generated from the comparison circuit (23). On the other hand, the output signal of the non-linear addition circuit (18) is applied to the clip detection circuit (24). Non-linear addition circuit (1
Since the output signal level of 8) is substantially constant, no output signal is generated from the clip detection circuit (24), that is, no clip is detected. Since no output signal is generated from the clip detection circuit (24), the input signal level is not reduced by the level variable circuit (25).

Further, when the input signal is large enough to cause clipping, the diodes (21) and (2)
2) One of the two becomes conductive and non-conductive, and the other output signal changes by limiting the level of one output signal of the amplifier (12) by the power supply voltage. The output signals of the positive and negative output terminals are signals as shown by the solid and dotted lines in FIG. Therefore, the signal flowing to the load (17) is a clipped signal as shown in FIG. Also, a non-linear addition circuit (18)
Is a signal as shown by a solid line or a dotted line in FIG. The output signal of the non-linear addition circuit (18) is applied to a comparison circuit (23) and compared with a reference voltage. The output signal of the comparison circuit (23) according to the comparison result is applied to the control terminal of the amplifier (12). On the other hand, the output signal of the non-linear addition circuit (18) is
4) is applied. The clip detection circuit (24) generates an output signal when the output signal of the non-linear addition circuit (18) is larger than the reference value.

At the time of clipping, the output signal of the nonlinear addition circuit (18) changes as shown in FIG. Utilizing this change, the clip detection circuit (24) detects the change in the output to detect the occurrence of a clip. The level varying circuit (25) varies the input signal level of the amplifier (12) so as to decrease according to an output signal from the clip detecting circuit (24) indicating that a clip has been detected. Therefore, since the input signal level is reduced in the amplifier (12), it is possible to prevent clipping of the output signal. In FIG. 1, a level variable circuit (25) for reducing the input signal level of the amplifier (12) is connected as means for preventing clipping.
The clip preventing means is not limited to this means, and other means conventionally used may be used.

FIG. 6 is a diagram showing a specific circuit example of a circuit that also serves as a comparison circuit (23) and a clip circuit (24). (26) and (27) are differentially connected.
A reference voltage is applied to one side and a non-linear addition circuit (1
8) a transistor to which the output signal is applied; (28) a current mirror circuit for inverting the collector current of the transistor (27); (29) a current mirror circuit for inverting the output current of the current mirror circuit (28); 30) and (31) are voltage dividing resistors connected between the power supply voltage Vcc and ground;
(32) is an output transistor whose base is connected to the connection middle point of the voltage dividing resistors (30) and (31), (33a) and (33b) are connected to the emitter and collector of the transistor (26), respectively, and the output current is This is a constant current source having a ratio of 2: 1.

In FIG. 6, when the base voltage of the transistor (27) is substantially equal to the base voltage of the transistor (26), that is, when the output signal of the nonlinear adder (18) is substantially equal to the reference voltage, the transistor (27) And (2
Since both 6) are turned on, the collector current of the transistor (27) becomes the difference current between the constant current sources (33a) and (33b). The collector current of the transistor (27) is inverted by the current mirror circuits (28) and (29),
The current mirror circuit (29) draws a current flowing through the voltage dividing resistor (30). The midpoint voltage of the voltage dividing resistors (30) and (31) becomes substantially 0 V, the output transistor (32) does not turn on, and no signal indicating that clipping has occurred is generated from the output terminal (34).

When clipping occurs and the output signal of the non-linear addition circuit (18) decreases as shown in FIG. 5 (c), the collector current of the transistor (27) decreases, and the output of the current mirror circuit (29) decreases. The current also decreases. Since the current flowing through the voltage dividing resistor (30) flows through the voltage dividing resistor (31), the midpoint voltage of the voltage dividing resistors (30) and (31) rises and the transistor (32) turns on. Therefore, an output signal indicating that the clip has been detected is generated from the output terminal (34).

Since the output current ratio of the constant current sources (33a) and (33b) is 2: 1, the transistor (26)
The output signal from the collector of the output terminal (3) is output when the voltage between the bases of the transistors (26) and (27) is 0V.
Does not occur from 5). When the base voltage of the transistor (26) is lower than the base voltage of the transistor (27), the output current of the constant current source (33b) is changed to the output terminal (3).
5). Conversely, when the base voltage of the transistor (26) is higher than that of the transistor (27), current flows from the output terminal (35) to the constant current source (35) via the transistor (26), and an output signal is generated. . The output signal from the output terminal (35) is applied to the control terminal of the amplifier (12) and controls the output DC level of the amplifier (12).

[0025]

As described above, according to the present invention, in an amplifier for lowering the output direct voltage to less than half the operating voltage and driving the load with a half-wave output signal, the output DC voltage is controlled. Since the signal level changes only when a clip occurs, the clip can be accurately detected based on the change, and a clip detection circuit suitable for the amplifier can be provided. .

Since the clip detection level can be changed only by the resistance, the detection level can be easily changed. Furthermore, since clip detection is not performed without using a signal supplied to the load, even if the output level of the output amplifier circuit changes according to the resistance value of the load, it is not affected at all,
Clip detection can be performed accurately, and there is no need to change the clip detection level according to the load.

[Brief description of the drawings]

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

FIG. 2 is a circuit diagram showing a conventional example.

FIG. 3 is a characteristic diagram for explaining the present invention.

FIG. 4 is a characteristic diagram for explaining the present invention.

FIG. 5 is a characteristic diagram for explaining the present invention.

FIG. 6 is a specific circuit example showing a main part of the present invention.

[Explanation of symbols]

 12 Amplifier 17 Load 18 Nonlinear circuit 19 Comparison circuit 24 Clip detection circuit 25 Level variable circuit

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H03G 5/00-11/08 H03F 3/68

Claims (2)

(57) [Claims] 1. A two input terminals, includes two output terminals and a control terminal for determining the DC level of the output terminal, and the amplifier that amplifying the input signal from one input terminal, one of said amplifier A non-linear addition circuit that clamps the other output signal of the amplifier to a predetermined level when the output signal level is equal to or higher than a predetermined value; and an output signal corresponding to a difference between an output signal of the non-linear addition circuit and a reference voltage. and a comparator circuit to be applied to the control terminal, the negative by the half-wave signals of opposite phase
A clip detection circuit of an amplifier that BTL-drives a load , comprising: a detection unit that detects a clip by detecting that an output signal of the non-linear addition circuit has become a predetermined value or more or a predetermined value or less from the reference voltage. A clip detection circuit, comprising: 2. The detecting section, which is also used as a non-linear addition circuit, wherein a first transistor to which an input signal is applied to a base, a bias is applied to a base, and an emitter is commonly connected to an emitter of the first transistor. A second transistor, and an output stage circuit that generates an output signal indicating whether or not clipping has been detected in accordance with an output signal generated from the collector of the first transistor. 2. The clip detection circuit according to claim 1, wherein an output signal is generated to a control terminal of the amplifier.