KR20050048425A - An analog/digital mixed-mode amplifier using ripple-feedback filter - Google Patents

Abstract

The present invention provides an analog amplifier which serves as an independent voltage source and supplies a current to compensate for the distortion caused by the digital amplifier; A current sensing amplifier configured to sense a current of the analog amplifier and generate an amplified voltage; An adder for summing the output of the current sense amplifier and the output of a ripple current sense amplifier; A digital amplifier receiving the output of the summer and controlling a switching operation to supply amplified current by driving a predetermined MOS switch; A ripple feedback filter for detecting a ripple component of a current of the digital amplifier; It provides an analog / digital hybrid amplifier using a ripple feedback filter comprising a; ripple current sensing amplifier for sensing the filtered signal of the ripple feedback filter to generate an amplified voltage.

According to the present invention, not only the loss of the analog amplifier can be reduced by using the ripple feedback filter, but also the quality of the output signal can be significantly improved.

Description

An analog / digital mixed-mode amplifier using ripple-feedback filter

The present invention relates to a hybrid amplifier using a ripple feedback filter, and more particularly, to use a ripple feedback to remove switching ripple of a digital amplifier in a hybrid amplifier combining a high linearity analog amplifier (AA) and a high efficiency digital amplifier. The present invention relates to a hybrid amplifier in which phase delay is eliminated.

1 is a circuit diagram of an analog / digital hybrid amplifier (basic MMA) in which an analog amplifier and a digital amplifier are simply cascaded.

The hybrid amplifier is a high-fidelity, high-efficiency amplifier that combines a high-fidelity analog amplifier with a high-efficiency digital amplifier.

FIG. 2 is a diagram illustrating an example of an operating waveform of an analog / digital hybrid amplifier (basic MMA) illustrated in FIG. 1. In this operation waveform, the digital amplifier 130 supplies current (id) corresponding to most of the output current to improve the efficiency, and the analog amplifier 110 reversely reverses the ripple current which is a necessary result of the switching operation of the digital amplifier. By compensating for distortion by supplying the analog current (ia), the analog / digital hybrid amplifier exhibits high fidelity characteristics comparable to that of a pure analog amplifier and high efficiency characteristics comparable to that of a digital amplifier. Here, the ripple current is a ripple component of the digital current id going out from the digital amplifier to the output side. In other words, the ripple component of the switching frequency component loaded on i _d is the ripple current.

The output voltage Vsen of the current sensing amplifier CSA1 120 is proportional to the output current ia that the analog amplifier provides to compensate for the ripple current in the digital amplifier. The output voltage Vsen inverts the switching of the digital amplifier above or below the hysteresis voltage Vh of the comparator CP, so that the oscillating switching frequency is a constant in which the current of the analog amplifier ia is defined as the hysteresis of the comparator. It is determined to be limited within the range.

FIG. 3 is a diagram for describing a relationship between a switching frequency of a simple analog / digital hybrid amplifier shown in FIG. 1 and a propagation delay or phase delay of a circuit. Looking at the process in which the switching frequency is determined in more detail, the half period of the switching frequency that is oscillated in FIG. 3 may be expressed by the following equation.

[Equation 1]

T / 2 = T _f + T _h + (T _a + T _d )

Here, Tf corresponds to the phase delay between the voltage Vd of the MOS switch and the output current id of the digital amplifier 130, which corresponds to approximately 90 in the case of a simple inductor (L1 in FIG. 1). . Th is a delay caused by the hysteresis of the comparator, and Ta and Td correspond to propagation delay times in the current sense amplifier and the gate driving circuit, respectively. When the switching frequency fsw determined through Equation 1 is obtained,

[Equation 2]

Becomes Where Vdd is the power supply voltage applied to the MOS switch of the digital amplifier, and Vhpp is the amplitude of the hysteresis voltage Vh of the comparator. Since the mixed amplifier shown in FIG. 1 is oscillated at a switching frequency given by Equation 2, the digital amplifier 130 generates a corresponding triangular wave form ripple current, and the analog amplifier 110 generates such a ripple current and magnitude. Is the same but reverses the current to compensate for the distortion. Through this operation, the analog current of the ripple component flows to the output side in the analog amplifier 110, and a loss occurs accordingly. The loss of the analog amplifier 110 is not a big problem when the mixed amplifier produces a large output. However, it is necessary to reduce the ripple current of the analog amplifier 110 because its effect is relatively large at low output or no signal and takes up most of the loss at no signal.

Among the methods of reducing the loss of the analog amplifier 110, there is a method of reducing the ripple magnitude of the current of the digital amplifier 130 by increasing the switching frequency, but it is difficult to increase the switching frequency by more than one in consideration of the stability of the circuit.

Therefore, the technical problem to be achieved by the present invention is to solve the phase delay problem caused by the ripple filter to obtain a sufficiently high switching frequency, thereby reducing the ripple component flowing to the analog amplifier to significantly improve the loss and fidelity of the analog amplifier. To provide an amplifier.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a ripple feedback filter capable of freely designing a multi-stage filter without having to consider stability and phase delay issues.

In order to achieve the above technical problem, the present invention provides an analog amplifier which serves as an independent voltage source and supplies a current to compensate for the distortion caused by the digital amplifier; A current sensing amplifier configured to sense a current of the analog amplifier and generate an amplified voltage; An adder for summing the output of the current sense amplifier and the output of a ripple current sense amplifier; A digital amplifier receiving the output of the summer and controlling a switching operation to supply amplified current by driving a predetermined MOS switch; A ripple feedback filter for detecting a ripple component of a current of the digital amplifier; It provides an analog / digital mixed amplifier using a ripple feedback filter comprising a; ripple current sensing amplifier for sensing the filtered signal of the ripple feedback filter to generate an amplified voltage.

In order to achieve the above technical problem, the present invention provides an inductor L1 connected to the amplifier for supplying the amplified current; An inductor L2 connected to the inductor L1 and a load; A capacitor having one end connected between the inductor L1 and the inductor L2; A resistor R2 connected to the other end of the capacitor and to ground; A ripple current sensing amplifier configured to sense a signal flowing through the ground at the resistor R2 and generate an amplified voltage; It provides a ripple feedback filter comprising a; adder for summing the output of the ripple current sense amplifier and the output of the current sense amplifier.

As a method of reducing the ripple current flowing from the digital amplifier to the output load side, the ripple filter shown in FIG. 4 may be considered.

4 is a diagram in which a ripple filter is added to the analog / digital hybrid amplifier shown in FIG. 1. However, this method also has a difficult problem to be applied to the hybrid amplifier. As shown in FIG. 4, when the ripple filter is installed at the output side of the digital amplifier 430, the current output from the digital amplifier 430 is delayed in phase while passing through the ripple filter 440, and is indicated by a thick line in FIG. 4. Increasing the overall delay time of loop 1 reduces the switching frequency, resulting in a significant increase in ripple current. Therefore, if the ripple filter is used in the hybrid amplifier as shown in FIG. 4, this results in a worse result than the simple hybrid amplifier shown in FIG. 1 using only one inductor without using the ripple filter.

FIG. 5A is an equivalent circuit diagram of a simplified ripple filter used in FIG. 4, and FIG. 5B is a board diagram of an impedance of the ripple filter shown in FIG. 4.

Figure 5a is a simplified representation of the ripple filter portion of Figure 4, the main inductor L1 of Figure 4 is equivalent to the current source in Figure 5a. Only the magnitude components of the complex impedances Z1 and Z2 for the rest of the filter are shown in FIG. 5B.

Referring to Z1 and Z2 shown in FIG. 5B, at the lower frequencies, Z1 is larger than Z2 at higher frequencies, and Z2 is larger than Z1 at higher frequencies. For, most of the digital current is filtered towards Z1 to the ground and the current through Z2 flows only the rest of the current.

FIG. 6 is a frequency board diagram of current flowing through the ripple filter to explain the phase delay of the ripple filter illustrated in FIG. 4.

Referring to FIG. 6 again, the board diagram of the current is drawn centering on the current flowing through the ripple filter 440 illustrated in FIG. 4. Where f2 is the frequency corresponding to w2 of FIG. 5B, at which point the digital output current id forms another pole in addition to the pole at the origin and decreases with a slope of 40 dB / dec.

As for the phase delay of the digital output current id, id has a phase delay of 90 degrees by the pole located at the origin, and additional phase delay is generated up to 180 degrees by the pole of f2.

According to Equation 1, Tf in Equation 1 corresponds to ∠I _d in FIG. 6, and a value obtained by adding Th + Ta + Td in addition to ∠I _d forms a half period of the switching frequency to switch. Therefore, as shown in FIG. 6, it can be expected that the switching frequency in the case of using the ripple filter will be determined at the point B at which the value of ∠I _d and ∠ (Th + Ta + Td) is 180 degrees. . Considering the hybrid amplifier shown in Fig. 1, the sum of the phase delays ∠I _d and ∠ (Th + Ta + Td) is 180 because the digital output current id has a slope of 20dB / dec and only 90 degrees of phase delay occurs. The point in degrees is point A, which has a high switching frequency corresponding to fsw. However, even if adding the ripple filter shown in Figure 4 to generate an additional phase delay due to filter ∠I _d and ∠ (Th + Ta + Td) crossing fsw in Fig go to point B, and the switching frequency fsw in the point A of Will be lowered to '.

Therefore, the use of the ripple filter in the method shown in FIG. 4 adversely affects the phase delay of the current feedback loop 1 of FIG. 4 and lowers the switching frequency, thereby increasing the ripple current and compensating for the loss in the analog amplifier. It is larger than a simple hybrid amplifier without the use of.

Referring again to the simple mixed amplifier of FIG. 1, the mixed amplifier of FIG. 1 has only one inductor L1 at the output side of the digital amplifier 130 as shown in FIG. 1. Therefore, in this case, since the phase delay is 90 degrees, the current feedback loop composed of the analog amplifier 110, the current sensing amplifier 120, and the digital amplifier 130 is stable, and the current of the digital amplifier 130 flowing through the inductor L1 is id. In addition to the ripple component of the analog amplifier 110 current ia to compensate for this and the output of the current sense amplifier CSA1 120 to detect this again has a triangular wave form. Therefore, even when using the ripple filter, the waveform and phase of the Vsen should have a triangular wave shape without additional phase delay other than the basic 90 degree phase delay caused by the filter as in the case of a simple mixed amplifier.

7 is a circuit diagram of an analog / digital hybrid amplifier using a ripple feedback filter according to an embodiment of the present invention.

A ripple filter and a ripple current sensing amplifier CSA2 760 for detecting the filtered ripple signal are added, and an output thereof is added to the output of the current sensing amplifier CSA1 720 at the summer 770 to add an input signal Vsen of the comparator 735. Configure

Unlike the method in which the ripple filter simply flows the filtered signal to the ground, the ripple feedback filter displays information about the ripple current filtered and pulled out to the ground, such as the analog amplifier AA (705), the current sensing amplifier (CSA1) 720, and the digital amplifier. It is characterized by mixing properly in the current feedback loop consisting of (730). Although the ripple filter is used through the feedback loop, the switching frequency is not affected by the filter by showing only the phase delay of the simple mixed amplifier without the ripple filter.

In the addition of the ripple current sensing amplifier CSA2 760, the construction method and the effect on the current feedback loop (loop 2) will be described as follows.

Assuming that the main inductor L1 751 in the configuration of the ripple feedback filter of FIG. 7 is sufficiently large as compared to the inductor L2 752, the ripple component of the current ids flowing in the L1 751 is represented by the inductor L1 151 shown in FIG. 1. The ripple of the triangular wave form as in the case of) and the input signal Vsen of the comparator 735 is given by the following equation.

[Equation 3]

V _sen = A1 * i _a + (-A2) * i _df =-(A1 * i _d + A2 * i _df )

In the above Equation 3, if the gain A1 of the current sensing amplifier CSA1 720 and the gain A2 of the CSA2 760 are set to the same value, Vsen is arranged as Equation 4.

[Equation 4]

V _sen = -A1 * (i _d + i _df ) = -A1 * i _ds

In the ripple feedback filter configured through the above-described form and design process, the input signal Vsen of the comparator 735 has a form proportional to ids as shown in Equation 4. In addition, as described above, ids is a triangular wave type having only 90-degree phase delay as shown in the mixed amplifier of FIG. 1, and thus, Vsen of FIG. 7 to which the ripple feedback filter of the present invention is applied has no additional phase delay in the current feedback loop (loop 2). It becomes a triangle-shaped waveform.

In the amplifier using the ripple feedback filter, the gain of the current sensing amplifier and the gain of the ripple current sensing amplifier are preferably equal to each other or have a gain ratio between 0.5 and 2.0. That is, it is preferable that the gain is the same order or 50% to 200%.

8 is a circuit diagram of an analog / digital hybrid amplifier using a two-stage ripple feedback filter according to an embodiment of the present invention.

The amplifier shown in FIG. 8 further develops the amplifier using the one-stage ripple feedback filter shown in FIG. It is preferable that the inductor L1 751 has a sufficiently large value than the inductor L2 752 and the inductor L3 756 so that the ripple component of the current ids flowing in the L1 751 becomes a triangular ripple. The ripple feedback filter illustrated in FIG. 8 used a two-stage ripple feedback filter to further improve the filter characteristics. Referring to the embodiment of FIG. 7 or FIG. 8 as described above, it is also possible to configure a multi-stage ripple feedback filter without reducing the switching frequency according to the phase delay.

There are several ways to detect when the ripple component of the amplified current supplied by the digital amplifier is filtered to ground. For example, it may be sensed using a current transformer instead of a resistor, or the filtered current may be estimated by using a resistor and checking the voltage across the resistor as in the example of FIG. 8. In FIG. 8, the resistor is connected to ground and receives a voltage across the resistor to sense the ripple current filtered by the ripple detector. The main feature of the present invention is not to throw the filtered ripple current to ground, but to use it again as switching information, not to specify the detection method. Therefore, the sensing method may be regarded as belonging to the scope of the present invention if the sensing method is used and the information is fed back.

9A and 9B show experimental waveforms during idle switching operations.

9A and 9B show experimental waveforms of the general ripple filter shown in FIG. 4 and the ripple feedback filter shown in FIG. 8 under an idle condition, respectively. As shown in FIG. 9A, the general secondary ripple filter simply bypasses the ripple current to ground, so the maximum f _sw cannot be higher than 115 kHz due to the phase delay of the filter. Such insufficient switching frequency results in much higher ripple current and higher P _idle than basic MMA without ripple filter. Therefore, the measurement result for such a case will be left out later. 9B shows a ripple feedback filter (one, two or more multistage filters) to improve switching frequency, ripple current, efficiency and THD. By applying this ripple feedback filter, V _sen becomes a triangular waveform without additional phase delay by the filter.

10A and 10B are diagrams showing experimental waveforms of the MMA using the basic MMA and the ripple feedback filter shown in FIG. 1 under a power transfer condition, respectively. Where i _d of MMA using the ripple feedback filter of FIG. The ripple component of ia is i _d in the basic MMA shown in FIG. Much smaller than the ripple component of ia.

11A and 11B are diagrams comparing idle power loss, power loss, and efficiency between a simple MMA and an MMA using a ripple feedback filter. P _idle vs. shown in FIG. 11A. Referring to f _sw , the idle power loss of the MMA using the ripple feedback filter is considerably reduced and 40W, about 36% of the simple MMA (110W) at the point of f _sw of 300 kH. 11B shows that when the output power is 50W, the power loss of the MMA using the ripple feedback filter is reduced to about 65% of the basic MMA and the efficiency is increased by about 15%.

FIG. 12 shows a comparison of total harmonic distortion (THD) between a basic MMA and an MMA using a ripple feedback filter. The total harmonic distortion of the MMA using the ripple feedback filter is much better than the total harmonic distortion of the basic MMA because the ripple is filtered in the ripple filter, and a THD of less than 0.01% is obtained.

It is not easy to apply a ripple filter to MMA because it can adversely affect stability. However, by using the ripple feedback filter, it is possible to freely design a multi-stage filter without having to consider the problems of stability and phase delay.

As described above, the present invention faithfully performs the filter function of removing the ripple component of the digital output current flowing from the digital amplifier to the output side by using the ripple feedback filter in the amplifier mixed with the analog amplifier / digital amplifier.

In addition, since the ripple filter can be freely configured without considering the problem of phase delay that may occur in the ripple filter used in the switching-powered device, it not only reduces the loss of the analog amplifier but also the quality of the output signal. It can be greatly improved.

When the present invention is applied to the acoustic amplifier (example of FIG. 7), the speaker will be a load, and when applied to a power supply, it can be a load such as a resistor. In addition, the present invention It may also be applied to the output ripple filter of the power converter for switching operation.

1 is a circuit diagram of an analog / digital hybrid amplifier in which an analog amplifier and a digital amplifier are simply cascaded;

2 is a diagram illustrating an example of an operating waveform of the analog / digital hybrid amplifier shown in FIG. 1;

FIG. 3 is a view for explaining a relationship between a switching frequency and a phase delay or a phase delay of a circuit of the analog / digital hybrid amplifier shown in FIG. 1;

4 is a diagram in which a ripple filter is added to the analog / digital hybrid amplifier shown in FIG. 1;

5A is an equivalent circuit diagram of a simplified ripple filter used in FIG. 4;

FIG. 5B is a board diagram showing an impedance of the ripple filter shown in FIG. 4;

6 is a frequency board diagram of a current flowing in the ripple filter to explain the phase delay of the ripple filter shown in FIG. 4;

7 is a circuit diagram of an analog / digital hybrid amplifier using an ripple feedback filter according to an embodiment of the present invention;

8 is a circuit diagram of an analog / digital hybrid amplifier using a two stage ripple feedback filter according to an embodiment of the present invention;

9A and 9B show experimental waveforms at idle switching operations;

10A and 10B show experimental waveforms of the MMA using the basic MMA and the ripple feedback filter shown in FIG. 1 under a power transfer condition, respectively;

11A and 11B show a comparison of idle power loss, power loss and efficiency between a basic MMA and an MMA using a ripple feedback filter.

FIG. 12 shows a comparison of total harmonic distortion (THD) between a basic MMA and an MMA using a ripple feedback filter.

Claims (10)

An analog amplifier serving as an independent voltage source and supplying current to compensate for distortion caused by the digital amplifier; A current sensing amplifier configured to sense a current of the analog amplifier and generate an amplified voltage; An adder for summing the output of the current sense amplifier and the output of a ripple current sense amplifier; A digital amplifier receiving the output of the summer and controlling a switching operation to supply amplified current by driving a predetermined MOS switch; A ripple feedback filter for detecting a ripple component of a current of the digital amplifier; And a ripple current sensing amplifier configured to sense the filtered signal of the ripple feedback filter and generate an amplified voltage. The method of claim 1, The ripple feedback filter An inductor L1 751 connected to a contact of the predetermined MOS switch; An inductor L2 752 having one end connected to the inductor L1; A capacitor 753 having one end connected between the inductor L1 and the inductor L2; And a resistor 754 connected to the other end and the ground of the capacitor. The other end of the inductor L2 (752) is an analog / digital mixed amplifier using a ripple feedback filter, characterized in that connected to the current sense amplifier 720 and the load. The method of claim 2 And the inductor L1 has a value sufficiently larger than that of the inductor L2 so that the ripple component of the current (ids) flowing in the inductor L1 becomes a triangular wave form ripple. The method of claim 1,  The ripple feedback filter An inductor L1 751 connected to a contact of the predetermined MOS switch; An inductor L2 752 having one end connected to the inductor L1; A capacitor 753 having one end connected between the inductor L1 and the inductor L2; A resistor 754 connected to the other end of the capacitor 753 and the ground; An inductor L3 756 having one end connected to the other end of the inductor L2; A capacitor 757 having one end connected between the inductor L2 and the inductor L3; And a resistor 758 connected to the other end of the capacitor 757 and the resistor 754. The other end of the inductor L3 756 is connected to the current sensing amplifier 720 and the load, The ripple current sensing amplifier is an analog / digital mixed amplifier using a ripple feedback filter, characterized in that for generating the amplified voltage by sensing the current flowing to the ground through the resistor (754) and the resistor (758). The method of claim 4 The inductor L1 has a sufficiently larger value than the inductor L2 and the inductor L3 so that the ripple component of the current ids flowing in the inductor L1 becomes a triangular wave form ripple. . The method according to any one of claims 1 to 5, The analog / digital hybrid amplifier using the ripple feedback filter, characterized in that the gain of the current sense amplifier and the gain of the ripple current sense amplifier is equal to each other or the ratio of the gain is between 0.5 to 2.0. An inductor L1 connected to the amplifier for supplying the amplified current; An inductor L2 connected to the inductor L1 and a load; A capacitor having one end connected between the inductor L1 and the inductor L2; A resistor R2 connected to the other end of the capacitor and to ground; A ripple current sensing amplifier configured to sense a signal flowing through the ground at the resistor R2 and generate an amplified voltage; And an adder for summing the output of the ripple current sense amplifier and the output of the current sense amplifier. The method of claim 7, And the inductor L1 has a value sufficiently larger than that of the inductor L2 so that the ripple component of the current ids flowing in the inductor L1 becomes a triangular wave form ripple. The method of claim 7, An inductor connected between the inductor L2 and the load; A capacitor having one end connected between the inductor and the inductor L2; And at least one filter unit including a resistor connected to the other end of the capacitor and the resistor R2. The method of claim 9 And the inductor L1 has a value sufficiently larger than that of the inductor L2 and the inductor such that a ripple component of the current ids flowing in the L1 becomes a triangular wave ripple.