High Dynamic Range Headphone Driver
Created: Feb 22, 2017
No description available.
In acoustics, dynamic range is the ratio between the loudest perceived signal and the quietest perceived signal. This ratio is measured in decibels (dB). For humans, the threshold of hearing is measured as 0dB SPL (sound pressure level) and the threshold of pain 120dB SPL. Therefore the dynamic range is 120dB. Dynamic range is not part of any headphone specification, but will help in benchmarking the isolation offered by the headphone in a noisy environment.
This reference design features a low-distortion, audio amplifier signal chain that utilizes THS4521 as the differential amplifier and OPA2836 as the headphone driver. The THS4521 amplifies the output of the audio DAC and also shifts the common-mode voltage to ground for the subsequent headphone driver stage. An alternative is to use two parallel single-ended amplifiers, but a fully differential amplifier (FDA). The OPA2836 has two functions: converts the differential output signal from the THS4521 to a single-ended signal and drives the headphone load. Both amplifiers have similar distortion specifications, so the first two options yield similar distortion performance. In this application, the OPA2836 is driving the heavy headphone load, while the THS4521 is driving a much lighter load formed by the input resistors of the second stage.
This design is specifically designed for headphones. An audio jack in this design enables testing with headphones. The design features an excellent performance-to-power ratio, making it an ideal choice for high dynamic-range audio applications.