Composition and classification of digital audio power amplifier

Digital audio power amplifier is an input analog audio signal or PCM digital information transforms into a PWM (pulse intensity modulation) or PDM (pulse density modulation) of the pulse signal, then the pulse PWM or PDM signal to control the power switching devices through on / off audio power amplifier. Also known as switching amplifiers, D class amplifier, with the outstanding advantages of high efficiency. Digital audio power amplifier is also looking into a bit of power for a digital-analog converter. Amplifier by the input signal processing circuit, the switch signal forming circuit, power switches, and low pass filter composed of four parts.

PWM input signal forming circuit sub-processor and two PDM processing the input signal amplitude transforms into a pulse width or pulse density changes.

High-power switching circuits separately bridge and full bridge (BTL connection) of two. High-power switching devices are used in the seventies bipolar transistor. But now almost only use the N-channel MOS-FET. Half-bridge way up and down two tubes when the working status of the opposite turns off, the two diagonal full bridge mode on the tube when the working status of the opposite turns off.

The role of low-pass filter is to form a beautiful whole pulse waveform simulation, that is filtered PWM or PDM signal carrier component. Often with little power loss LC-type filter.

Digital amplifier circuit is the most classical form of switch signals the use of voltage comparator circuit and triangular wave generator means. With the triangular wave generator's amplitude triangular test compared with the analog voltage signals, and transform into a PWM signal. This inconsistent way vulnerable component parameters and parameter changes, usually negative feedback should be introduced in the input.

△ Σ-based PDM digital amplifier is the approach companies such as Sharp, also known as a bit △ Σ amplifier. Switch signal forming circuit using a bit of △ Σ modulator output, use it to transform the analog signal into a PDM signal. Usually to improve linear, from the output body △ Σ the introduction of a negative feedback modulator.

The above two kinds of digital amplifier input signals are analog signals. Now has a digital sound source, sound source, so their all-digital amplifier digital amplifier has become an inevitable trend. △ Σ-type PWM digital amplifier is a fully digital amplifier ways, the all-digital amplifier signal the beginning of the formation of the circuit from the bit converter and PWM transform circuit. bit transform the role of the circuit is to transform the input PCM signal into a low-bit PCM signal, and then by the PWM conversion circuit to low bit The PCM signal transformation into a PWM signal. bit high-end products and reduce the bit-band signal to noise ratio deterioration caused by compression, using a multi-bit output of △ Σ modulator. in the PWM circuit is used for feedforward compensation, output two 8 BTL drive PWM signal. The two PWM signals with Eagle Road, opposite, and were 2 up thousands of the relationship between characteristics of the output group of switching devices due to the error in power at the beginning of transformation circuit cancel each other out. so this circuit can be done to the distortion introduced and does not change the negative feedback.

PDM signal is the same amplitude and time width of the pulse, the pulse density is simulated and changed. So PDM signal amplitude and time axis is a bit of the signal. The PWM signal is the amplitude and frequency of a pulse, pulse width With the analog signal amplitude and change. Therefore, the amplitude of the PWM signal to set the direction of the signal a bit. PDM way to ensure that the same signal to noise ratio and dynamic range, using the switching frequency than the PWM approach to municipal, city of the switching frequency several MHz, for example, Sharp's SM-SX2000 switching frequency on the way up to 5.6448MHz.PWM switching frequency can be lower, but the main clock frequency than the city, as the switching frequency of 2 times the N-th power.

City of the first frequency PDM way, so you must use the input switching device off small, but this type of switching device on-resistance is often too great. On the contrary, PWM mode, you can use a smaller switch on-resistance devices, so at the beginning of the circuit efficiency of about 85%, but the general PWM amplifier can be more than 90% efficiency.

Currently, TI, Sony, etc. have been developed for digital audio amplifier application specific integrated circuit, and using them to produce a variety of integrated digital amplifier, and some products are the noodles market products developed by end users. At the same time each company is also true for the sector to reduce all kinds of soldiers.