JPH0367364B2 - - Google Patents

Description

Detailed Description of the Invention The present invention detects distortion occurring in a signal path having filter characteristics and feeds it back to the input side of the signal path. The present invention relates to a distortion removal circuit that removes distortion in a filter signal passing frequency region.

As one of distortion reduction techniques for reducing distortion generated in an amplifier circuit or the like, various feedback techniques are known in which signals obtained at each point of a signal path of an amplifier circuit are fed back to the input side. FIG. 1 is a block diagram showing an example of an amplifier circuit using such multiple feedback technology. In this figure, 1 is an amplifier, which includes an amplifier 2 which is an ideal amplifier that does not generate distortion, and an adder which virtually adds the distortion generated by the amplifier 1 as a disturbance to the output of the amplifier 2. 3 and 3 equivalently represent the functions of the amplifier 1. Further, 4 is a feedback path with a gain of +1 that feeds back the input signal of the amplifier 1 to the adder 5, and 6
is a feedback path with a gain β that feeds back the output signal of the amplifier 1 to the adder 5. The adder 5 adds the input signal supplied via the signal input terminal 7 and the first and second feedback signals supplied via the feedback paths 4 and 6, respectively, and supplies the result to the amplifier 1. The amplified signal here is supplied to the signal output terminal 8. In this case, if the voltage of the input signal is Vi, the voltage of the output signal of the amplifier 1 is Vo, and the voltage of the distortion component added by the adder 3 is Vd, then the first feedback signal output from the feedback path 4 is The voltage becomes Vo-Vd/A, and the voltage of the second feedback signal output from the feedback path 6 becomes βVo. Therefore, the input/output conditions for the adder 5 on the input side are determined as follows: Vi+Vo-Vd/A+βVo=Vo-Vd/A (1). If we rearrange this equation (1), we get Vi=−βVo...(2). Therefore, as is clear from equation (2), if the feedback path 6 is not distorted, the output signal obtained at the signal output terminal 8 will not be distorted.

By the way, distortion removal circuits using multiple feedback technology have been devised and implemented in general amplifier circuits as mentioned above, but this is still not possible in signal systems such as class D amplifiers with filter characteristics. There is no distortion removal circuit that uses such multiple feedback technology, and the development of such a circuit has been strongly desired.

In view of the above points, the present invention provides a distortion removal circuit that can remove distortion in a signal system having filter characteristics without changing the characteristics of the signal system. an input feedback path that has filter characteristics equivalent to the frequency characteristics and receives the signal voltage at the input end of the signal path; an output negative feedback path that receives the output voltage of the signal path; The present invention is characterized in that a feedback calculation circuit is provided that oxidizes the output voltage and the output voltage of the output negative feedback path to the input signal voltage to be amplified, and applies the voltage to the input end of the signal path.

Embodiments of the present invention will be described below with reference to the drawings. First, the operating principle of the distortion removal circuit according to the present invention will be explained with reference to the block diagram shown in FIG. In FIG. 2, parts corresponding to those in FIG. 1 are given the same reference numerals. In this figure, 2a is an amplifier that equivalently represents the distortion-free signal transfer characteristics of amplifier 1a, and this amplifier 2a has predetermined filter characteristics.
Further, 9 is a filter circuit having filter characteristics equivalent to those of the amplifier section 2a.
In the distortion removal circuit shown in this figure, the filter circuit 9 feeds back the input signal of the amplifier 1a to the adder 5 (feedback operation circuit), and similarly, the feedback path 6 (output negative feedback path) feeds back the input signal of the amplifier 1a to the adder 5 (feedback calculation circuit). The output signal is fed back to the input side of the amplifier 1a. Here, the transfer function of the amplifying section 2a is
AT(s), the transfer function of the filter circuit 9 (input feedback path) is T(s), and the voltage of the signal input via the signal input terminal 7 is Vi, the signal output terminal 8
Let Vo be the voltage of the output signal obtained in , and Vd be the voltage of the distortion component added by the adder 3, then the voltage of the signal input to the filter circuit 9 will be Vo-Vd/AT(s). Therefore, the voltage of the first feedback signal output from the filter circuit 9 is Vo-Vd/A. Further, in this case, the voltage of the second feedback signal output from the feedback path 6 is βVo. Here, the input condition for the adder 5 is determined as Vi+βVo+Vo−Vd/A9Vo−Vd/AT(s) (3). And if we rearrange this equation (3) with respect to Vi, we get Vi=(1/AT(s)-1/A-β)Vo+(
1/A-1/AT(s))Vd = 1-T(s)-AT(s)β/AT(s)
Vo+T(s)-1/AT(s)Vd...(4). Therefore, Vo is Vo=AT(s)/1-T(s)-AT(s)β
Vi+1-T(s)/1-T(s)-AT(s)βVd……(5
) becomes. Here, the gain β of the feedback path 6 and the amplifier section 2a
If the gain β of the feedback path 6 is set so that the constant part of the transfer function AT(s) of the gain A satisfies the function β=-1/A...(6), then (5) Vo shown in the formula is Vo=AT(s)Vi+[1-T(s)]Vd (7). In this case, Vd in the second term on the right side of equation (7) is equal to Vd, which is usually less than 1 [1-T
(s)], the distortion of the output signal obtained at the signal output terminal 8 is lower than the distortion generated by the amplifying section 2a, and especially T(s)
In the region where =1, the distortion becomes zero. In this case, AT(s)Vi in the first term on the left side of equation (7) indicates the signal component when the signal input via the signal input terminal 7 is amplified only by the amplifying section 2a. That is, the filter characteristics of the amplifying section 2a are preserved as they are.

A first embodiment of the distortion removal circuit according to the present invention based on the above-mentioned principle will be described below with reference to the circuit diagram shown in FIG. In FIG. 3, the signal input terminal 3 is connected to the operational amplifier 1 via a resistor 10 (value R).
It is connected to the inverting input terminal of 1. The hydrochloric acid amplifier 11 constitutes the adder 5 (feedback calculation circuit), and the non-inverting input terminal of the operational amplifier 11 is grounded, and the output terminal is connected to the input terminal of the operational amplifier 11 via a resistor 12 (value R). It is connected to the inverting input terminal, and also to the input terminal of the filter circuit 9a (input feedback path) and the input terminal of the amplifier 2a-1. Amplifier 2a- ₁ has a gain of -A,
The output terminal of the amplifier 2a- ₁ is the filter circuit 2a.
– Connected to the ₂ input terminals. The filter circuit 2a- ₂ is a circuit having filter characteristics with a transfer function of T(s), and the output terminal of the filter circuit 2a- ₂ is connected to the adder 3. Adder 3
is hypothetically provided to show that the distortion (Vd) generated in the amplifier 1a (signal path) composed of the amplifier 2a- ₁ and the filter circuit 2a- ₂ is included in the output of the amplifier 1a. The output terminal of the adder 3 is connected to the signal output terminal 8.

Further, the filter circuit 9a is the filter circuit 2a.
− Transfer function Tf(s) equivalent to the transfer function T(s) of ₂
The output terminal of the filter circuit 9a is connected to an operational amplifier 14 via a resistor 13 (value R).
is connected to the inverting input terminal of Further, the signal output terminal 8 is connected to the inverting input terminal of the operational amplifier 14 via a resistor 15 output negative feedback path (value AR). The operational amplifier 14 is a filter circuit 9a.
The feedback component signal of the input signal of the amplifier 1a is supplied through the amplifier 1a and the feedback component signal of the input signal of the amplifier 1a is supplied through the resistor 15.
It adds (computes) the output signal of a,
The non-inverting input terminal of the operational amplifier 14 is grounded,
The output terminal is connected to the inverting input terminal of the operational amplifier 14 via a resistor 16 (value R), and
It is connected to the inverting input terminal of the operational amplifier 11 via a resistor 17 (value R).

Next, the operation of the circuit having the above configuration will be explained using mathematical formulas. First, if the voltage of the output signal obtained at the signal output terminal 8 is Vo, the voltage of the signal input to the amplifier 1a is -Vo - Vd/AT (s), and the voltage of the signal output from the filter circuit 9a is Ha-
Tf(s)/AT(s)(Vo−Vd). And resistance 1
The value of 6 is R, the value of resistor 13 is R, and the value of resistor 15 is
Since it is AR, the voltage of the signal output from the operational amplifier 14 is Tf(s)/AT(s)(Vo-Vd)-Vo/A. Therefore, to find the output condition at adder 5, -Vi-Tf(s)/AT(s)(Vo-Vd) +Vo/A=-Vo-Vd/AT(s)...(8) Become. And if we rearrange this equation (8) with respect to Vi, we get Vi=+Vo+Vd/AT(s)[-Tf(s)+1]+Vo/A=Vo/A[-Tf(s)/T(s)+1/T (s)+
1] -Vd/AT(s) [1-Tf(s)] ...(9) Therefore, Vo is Vo=AT(s)/1+T(s)-Tf(s)Vi+
1-Tf(s)/1+T(s)-Tf(s)Vd...(10). Here, the transfer function T(s) of the filter circuit 2a- ₂ and the transfer function Tf(s) of the filter circuit 9a are
are equal, so Vo shown in equation (10) is Vo=AT(s)Vi+[1-T(s)]Vd (11). Therefore, as is clear from equation (11), the transfer function T(s) of the filter circuit 14 is T
In the region where (s)=1, the voltage Vo of the output signal is Vo=AT(s)Vi (12) and does not include distortion. Furthermore, in this case, in the region of T(s)=1, the operational amplifier 14
Since the voltage of the signal outputted from the amplifier is an extremely small voltage of -Vd/A, the dynamic range of the feedback circuit including the operational amplifier 14 can be reduced.

As can be seen from equation (10), the filter circuit 2a-
Even if the transfer function T(s) of ₂ and the transfer function Tf(s) of the filter circuit 9a do not completely match, the circuit system is stable unless T(s)-Tf(s)=-1. It is. That is, both filter circuits 9
Unless a, 2a- ₂ are high-order filters, and the orders of both filter circuits 9a, 2a- ₂ are not significantly different (one filter circuit's phase rotation is slow, the other filter circuit's phase rotation is fast). ), the above-mentioned state of T(s)-Tf(s)=-1 can hardly occur, and therefore, the distortion generated in the amplifier 1a can usually be reduced without any problems.

Furthermore, as is clear from equation (11), if both filter circuits 9a and 2a- ₂ are filters having, for example, a low-pass filter characteristic of 1/1+ST, the voltage Vo of the output signal is Vo=A/1+STVi+( 1-A/1+ST)Vd...(13) Therefore, in this case, unless ST=-1, that is, unless the filter circuits 9a and 2a- ₂ lose their filter characteristics, the output signal will contain Distortion can be reduced.

Next, FIG. 4 is a circuit diagram showing a second embodiment of the distortion removal circuit according to the present invention. In this figure, the operational amplifier 11 in the adder 5b has its non-inverting input terminal connected to the signal input terminal 7, and
The inverting input terminal is connected to the operational amplifier 14 via the resistor 17.
is connected to the output terminal of the operational amplifier 11.
A resistor 12 is inserted between the output terminal and the inverting input terminal. In addition, a resistor 18 (value (2A-1)r) and a resistor 1 are connected between the signal output terminal 8 and the ground point.
9 (value r) are successively inserted in series, and the connection point of these resistors 18 and 19 is connected to the non-inverting input terminal of the operational amplifier 14. and operational amplifier 14
The inverting input terminal of the operational amplifier 14 is connected to the output terminal of the filter circuit 9a through a resistor 13, and the output terminal of the operational amplifier 14 is connected to the inverting input terminal through a resistor 16. Also, here, amplifier 2a- ₁
The gain of is A, and the transfer function of the filter circuit 9a is T.
(s).

In the above configuration, if the voltage of the output signal obtained at the signal output terminal 8 is Vo, the voltage of the signal input to the amplifier 1a is Vo - Vd/AT (s), and the signal output from the filter circuit 9a is The voltage of
Vo-Vd/A, and this signal is supplied to the non-inverting input terminal of the operational amplifier via the resistor 13. Further, since the ratio of the values of the resistors 18 and 19 is (2A-1):1, the voltage supplied to the non-inverting input terminal of the operational amplifier 14 is Vo/2A. Therefore, the voltage of the signal output from the operational amplifier 14 is -
Vo−Vd/A+Vo/A. Here, the input/output conditions for the adder 1 are determined as follows: Vi+[Vi-(-Vo-Vd/A+Vo/A)]=Vo-Vd/AT (14). If we rearrange this equation (14) with respect to Vi, we get 2Vi=1/AT(s)Vo+Vd/A-Vd/AT(s)=
1/AT(s)Vo+T(s)G-1/AT(s)Vd...(15
) becomes. Therefore, Vo becomes Vo=2AT(s)Vi+[1-T(s)]Vd (16). As a result, when T(s)=1, such as when both filters 9a and _2a-2 have flat passbands for the input signal, the distortion voltage
Vd is completely canceled and Vo=2AT(s)Vi...(17). Therefore, in this case as well, the output signal does not include distortion.

As explained above, the distortion removal circuit according to the present invention has filter characteristics equivalent to the frequency characteristics set in the signal path, and includes an input feedback path that receives the signal voltage at the input end of the signal path, and an output negative feedback path that inputs the output voltage of the input feedback path, and adds the output voltage of the input feedback path and the output voltage of the output negative feedback path to the input signal voltage to be amplified, and sends the signal to the input end of the signal path. Since a feedback calculation circuit is provided to apply the signal, distortion in the signal path can be reduced without changing the filter characteristics of the signal path, and can be reduced to almost zero under certain conditions. Therefore, when the distortion removal circuit according to the present invention is applied to a class D amplifier having filter characteristics, the distortion of the amplifier can be eliminated without changing the characteristics of the amplifier in any way.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing an example of an amplifier circuit using multiple feedback technology, Fig. 2 is a block diagram showing the operating principle of a distortion removal circuit according to the present invention, and Fig. 3 is a block diagram showing an example of the distortion removal circuit according to the invention. FIG. 4 is a circuit diagram showing an embodiment of the distortion removal circuit according to the present invention.
It is a circuit diagram showing an example of. 1a... Signal path (amplifier), 5... Feedback calculation circuit (adder), 9a... Input feedback path (filter), 15... Output negative feedback path (resistance).

Claims (1)

[Scope of Claims] 1. A signal path configured to voltage-amplify an input signal to be amplified while giving it a set frequency characteristic without depending on the characteristics of the load, and drive the load with the amplified output. In a distortion removal circuit for removing distortion of the signal path, the input feedback path has filter characteristics equivalent to the frequency characteristics set in the signal path and receives the signal voltage at the input end of the signal path; an output negative feedback path that receives an output voltage; an output voltage of the input feedback path and an output voltage of the output negative feedback path are added to the voltage of the input signal to be amplified; 1. A distortion removal circuit comprising: a feedback calculation circuit for applying voltage.