TW200937994A - Sound driving circuit for reducing pop noise during powering on and off - Google Patents

Abstract

A sound driving circuit for reducing pop noise during powering on and off comprises a reference voltage generator for generating a reference voltage signal, a low pass filter with at least 2nd order filter for receiving the reference voltage signal and generating a filtered reference voltage signal, and a driving unit for receiving an input audio signal and the filtered reference voltage signal, thus to generate an output audio signal. Because the variation of the filtered reference voltage signal is reduced, the pop noise during powering on and off is also reduced.

Description

200937994 IX. Description of the Invention: [Technical Field] The present invention relates to a sound driving circuit for reducing the popping sound of a switching machine, and more particularly to a reference voltage variation amount when a low-pass filter of a second or second order is used to control a switching machine Sound drive circuit. [Prior Art] Fig. 1 is a conventional sound driving circuit. As shown in the figure, the sound driving circuit 10 includes a reference voltage generating unit u, a reference voltage stabilizing unit 7L 12, and an audio driving unit 13. In general, the sound driving circuit 10 is a single-supply driving circuit, and therefore the reference voltage generating unit η is used to generate the reference voltage Vref of the 1/2 power supply voltage (Vcc/2) to the audio driving unit 13. After the reference voltage Vref is stabilized, the audio signal is input by vin, and the user can listen to the music output from the audio driving unit 13 from the headphone (HP) 14. In order to stabilize the reference voltage Vref, the reference voltage stabilizing unit 12 is normally disposed between the reference voltage generating unit 11 and the audio driving unit 13. As shown in Figure i, the general reference voltage stabilizing unit n is a first-order low-pass filter to filter high-frequency noise from the power supply voltage Vcc. In order to reduce the generation of the pop-up of the switch, the reference voltage vref is output as a ramp for a sufficient period of time, such as a few hundred milliseconds. When the power is turned on and off, the waveforms of the reference voltage Vref, the 〇p amplifier 13b, and the output voltage of the audio driving unit 13 are the Chuan, Chuan, and F13 of the i-th diagram. Therefore, when the switching signal ENB is turned on as shown by the waveforms F11, m, and yang, the reference voltage and the 〇p amplifier i3i will have a rapid change, so that the output voltage of the audio driving unit 13 will surge. The generation of the sound of the switch.

There are currently some known techniques to reduce the amplitude of the sound of the switch. For example, U.S. Patent No. 6,775,387, "Three-step ramped reference to reduce popping noise on audio circuit", U.S. Patent No. 7,167,569, "with Dynamic Planning" "Output coupling capacitor free audio power amplifier dynamically configured for speakers and headphones with excellent click and pop performance", and U.S. Patent No. 7,183,857 "Single supply direct drive amplifier", U.S. Patent No. 6,774,684, "Circuits and methods for controlling transients during audio device power", "Circuits and methods for controlling transients during audio device power" -up and power-down, and systems using the same)", U.S. Patent No. 6,940,345, "Supplying a ramp voltage to an amplifier", and U.S. Patent No. 7,254,244 "Pop and click reduction using DAC power up and power down processing". However, these conventional techniques are all dealt with for ramp voltage or power supply voltage, and are not mentioned or referenced. Voltage is designed and processed. Moreover, these conventional techniques are relatively complicated. 7 200937994 [Summary of the Invention] The present invention has the problem that the sound driving circuit for reducing the popping sound of the switching machine is directly connected in series with the second and second low-pass filters of the reference voltage generating unit.

In order to achieve the above object, the sound drive circuit of the present invention for reducing the popping sound of the switch machine comprises a reference voltage generating unit for generating a reference voltage, and a low pass filter unit having at least a second order low pass filter for receiving After the reference voltage is generated, a reference voltage is generated, and a driving unit receives an audio input signal and the filtered reference voltage, and generates an audio output signal. The low-pass filter of the low-pass filter unit controls the amount of change of the corresponding reference voltage when the switch is turned on, thereby reducing the pop-up of the switch. [Embodiment] Hereinafter, a sound driving circuit for reducing the popping sound of a switch machine according to the present invention will be described in detail with reference to the drawings. Fig. 2 is a view showing the sound driving circuit for reducing the popping sound of the switch machine according to the present invention. For example, the sound driving circuit 20 includes a reference power generating unit I, a reference voltage stabilizing unit 22, and an audio driving unit 13. The sound driving circuit 20 is a single power supply driving circuit, and therefore the reference voltage generating unit 11 is used to generate the reference voltage Vref of the 1/2 power supply voltage (Vcc/2) to the audio driving unit 13. In order to stabilize the reference voltage Vref, a reference voltage stabilizing unit 22 is disposed between the reference voltage generating unit 11 and the audio driving unit 13. As shown in FIG. 2, the reference voltage stabilizing unit 22 is an 8 ❹ ❹ SClRl-^l / „ = 0.3183/3⁄4 200937994 second-order low-pass chopper, so that the audio noise is excessively passed, thereby reducing the sound of the switch. The reference voltage generating unit u includes _ switching transistors τι and two voltage dividing resistors, then the voltage resistors have the same resistance value, and the voltage dividing resistors ru1, RU2 can generate 1/2 power voltage ( The reference voltage Vref of Vcc/2). The reference voltage stabilizing unit 22 is a second-order low-pass filter comprising two series-connected Rc circuits R3, R3,

Cl’. The audio driving unit 13 is a general standard 〇p amplifier driving circuit, and includes an OP amplifier 输出, an output capacitor, and two resistors R4 (input resistor) and R5 (feedback resistor). Wherein, the positive input terminal of the OP amplifier H)3 receives the output voltage of the reference voltage stabilization ... 2, that is, the reference voltage vref, the negative input terminal of the 〇P amplifier 103 receives the input signal Vin via the wheel resistance R4, and the OP amplification H 1 The output of 〇3 is connected to the negative input via feedback resistor R5 and outputs a signal via output capacitor C3. Figure 3 is a circuit of a general one-p-waveper. The first-order filter unit 31 includes a resistor R1 and a capacitor C1. If the magic is 5 〇 κ ohms, and ^ is 10 uF ′, then the mathematical mode of the first-order filter 31 is as follows:

Vout 1 Bu·

CIRI 〇〇 => 201og(—)«36ί/5 fn That is, at 20 Hz, 'Vout is approximately 36 dB. Figure 4 shows the circuit of a general second-order waver. 4, ^ Circuit The second-order filter 41 includes two RC circuits R1, Cl, R: > ^ %C2 connected in series. If R1 and R2 are 25K ohms and C1 and C2 are 5uF, then 兮-the number of each of the ^th order filters 41 is as follows:

Vout^ 1

Vin ^2C\C2R\R2 + S[C\R\ + C2(Rl + R2)] +1 , / =1.273273⁄4, ζ = ClRl^C2^Rl 13^. = 1 5 ylC\C2R\R2 2^ C\C2R\R2 => 401〇g(-) «47.8^5 fn That is, at 20Hz, Vout is attenuated by about 48dB. Ο ❹ Therefore, from the frequency domain analysis, at 20 Hz, the first-order chopper 41 attenuates the noise of the popping noise by about 12 dB, and the audio signal is distributed between 20 Hz and 20 kHz. Therefore, for noise removal above 2 Hz, there can be more obvious benefits. Figure 5 shows the change of the ramp waveform of the first-order and second-order filters when the switch is turned on. Figure 6 shows the change of the ramp waveform of the first-order and second-order filters when the switch is off (OFF). As can be clearly seen from Figs. 5 and 6, in the time domain/7 analysis, the first-order filter is relatively smooth at the starting point of the ramp waveform change', so that the amount of popping can be reduced. Further, by comparing the waveforms F11 and F12 of Fig. 1 with the waveforms F21 and F22 of Fig. 2, it can be understood that the change of the reference voltage Vref of the present invention is relatively gentle at the time of power-off, and therefore the change in the response to the output signal is also moderated. Therefore, the popping sound generated by the team or the earphone when the machine is turned on and off is relatively reduced, as shown by waveforms F13 and F23. The sound drive circuit of the present invention for reducing the popping sound of the switch machine can effectively reduce the amount of popping by using only a low-pass filter of a 13⁄4 or higher order to alleviate the change of the reference voltage Vref when the switch is turned on and off. Therefore, the present invention reduces the sound of the popping sound of the switch, and the regional circuit is handed over to the conventional technology. 200937994 The power saved by the ramping or the power supply voltage is saved. The present invention is described in the above, but the scope of the invention is not limited by the scope of the invention. μ 仃 可 可 【 【 【 【 【 【 简单 简单 简单 简单 简单 第 第 第 第 第 第 第Fig. 2 is a view showing the sound driving circuit for reducing the popping sound of the switch machine according to the present invention. Figure 3 shows the circuit of a general first-order filter. Figure 4 shows the circuit of a general second-order filter. Figure 5 shows the variation of the ramp waveform of the first-order and second-order filters when the switch is turned on (ΟΝ). Figure 6 shows the variation of the ramp waveforms of the first and second order filters when the switch is off (〇FF). Pattern No. 10, 20 Sound driving circuit 11 Reference voltage generating unit 12, 22, 31, 41 Reference voltage stabilizing unit 13 Audio driving unit 131 Operational amplifier 14 Headphones R111, R112, Rl, Rl', R2, R4, R5 Cl, Cl', C2, C3 Capacitor T1 Switching Transistor

Claims (1)

200937994 X. Patent application scope: 1. A sound driving circuit for reducing the popping sound of a switch machine, comprising: a reference voltage generating unit for generating a reference voltage; and a low pass filtering unit having at least a second order low pass filter. And after receiving the reference voltage, generating a filtered reference voltage; and an audio driving unit receiving an audio input signal and the filtered reference voltage, and generating an audio output signal. 2. The sound driving circuit for reducing the popping sound of a switch machine according to the first aspect of the patent application, wherein the low pass filtering unit is a second order low pass filter. 3. The sound driving circuit for reducing the popping sound of a switch machine as recited in claim 2, wherein the second-order low-pass filter comprises two series-connected resistor/capacitor circuits. 4. The sound driving circuit for reducing the popping sound of a switch machine according to claim 1, wherein the reference voltage generating unit comprises: a switching transistor that receives a power supply voltage for controlling an output of the reference voltage; Two series-connected voltage dividing resistors are connected to the switching transistor, and generate the aforementioned reference voltage at the junction of the series-dividing resistors. 5. The sound driving circuit for reducing the popping sound of the switch machine according to the first aspect of the patent application, wherein the audio driving unit comprises: an OP amplifier, the positive input end of the OP amplifier receives the output voltage of the reference voltage stabilizing unit; a resistor, one end receives the aforementioned audio input signal, and the other end is connected to the negative input end of the OP amplifier; 12 200937994 A feedback resistor has one end connected to the output end of the 〇p amplifier, one end connected to the negative input terminal of the PMOS amplifier, and one output capacitor connected at one end to the output end of the PMOS amplifier and the other end outputting a signal. 13