The TinyAmps uses the latest digital audio technology for amplification – from the market leader: Texas Instruments Inc.
The PurePath Digital technology was developed in Denmark, it started with a modulator (see below) and has since progressed into a complete range of audio chip devices.
The technology is based on a pulse-code-modulated (PCM) to pulse-width-modulated (PWM) converter called a modulator.
The modulator receives the audio in PCM (I2S) 24-bit audio format with a sample rate depending on the input. In a PCM signal format each sample has a assigned amplitude, see below (left side). PWM format signal (right side) has the magnitude for each sample descriped as a width as oppose to a height in PCM signal. The signal is up-sampled eight times internally (e.g. 8 x 48kHz = 384kHz) and then the modulator converts the signal to PWM with 384kHz switching frequency.
The sample rate is 44.1kHz or 48kHz if the Squeezebox® is used (depending on audio data). The amplifier selects automatically the sample rate and can run with up to 96kHz. No up or re-sampling is used.
To compare, a CD-player uses 44.1kHz and DVD-player 48kHz. CD/DVD players that specify higher sample rates are using up-sampling. The Transporter can run up to 96kHz sample rate depending on audio data.
The amplifier accepts digital audio input with a maximum audio sample word length of 24-bits.
The modulator also has build in digital audio processing with many possibilities.
The PWM signals for each channel is connected to the inputs of the power stage, where the PWM signals are internally level shiftet and fed into two sets of N-channel DMOS power transistors. The power stage is designed in a stereo Brigde-Tied-Load (BTL / full H-brigde) configuration, using a ½ H-bridge (one set of transistors) for each of the four speaker connections.
Passsive LC low-pass filter
The PWM output from the power stage filtered just before the speaker terminals using a second order LC low-pass filter.