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SPDIF Decoder ICs for Audio Applications

SPDIF Decoder ICs for Audio Applications

Introduction

The Sony/Philips Digital Interface (SPDIF) is a standard digital audio transfer format used to connect digital audio devices. SPDIF allows the transmission of digital audio signals from sources like CD players, TVs, computers etc to receivers and amplifiers. To decode the SPDIF signal back into analog audio, SPDIF decoder integrated circuits (ICs) are used. In this article, we will look at some of the key SPDIF decoder ICs used in audio applications.

Popular SPDIF Decoder ICs

CS8416

The CS8416 from Cirrus Logic is a widely used SPDIF receiver chip. Key features:

  • Supports up to 192kHz sampling rate
  • Includes analog voltage output DAC
  • Integrated phase-lock loop for clock recovery
  • Digital de-emphasis filter

WM8904

The WM8904 from Wolfson Microelectronics contains a high-quality SPDIF receiver suitable for audiophile applications.

  • Supports up to 192kHz sampling rate
  • Advanced jitter rejection features
  • Selectable digital filters
  • Integrated headphone driver and analog volume control

PCM9211

Texas Instruments PCM9211 is a low-power SPDIF receiver optimized for portable applications.

  • Supports sample rates up to 96kHz
  • Integrated headphone amplifier
  • Advanced pop/click suppression
  • Small VQFN package
ICMax Sample RateKey FeaturesApplications
CS8416192kHzDAC, PLL, De-emphasisA/V Receivers
WM8904192kHzJitter rejection, FiltersAudiophile
PCM921196kHzHeadphone amp, Pop/click suppressionPortable

Comparison

As seen from the table above, the key differences between various SPDIF decoder ICs are the maximum sampling rate support, features like jitter rejection or click suppression, integrated peripherals like DAC or headphone amp and target application area. The CS8416 offers full high-res support with additional features for home theater receivers. The WM8904 focuses on audiophile performance. And the PCM9211 is designed for portable use.

SPDIF Decoder Configuration

Typically, integrating an SPDIF decoder IC into a design involves:

  • Connecting the SPDIF input pin to a receiver or optical input module. This carries the SPDIF bitstream.
  • Providing the master clock to the decoder IC, usually through a crystal oscillator.
  • Configuring the chip features through the SPI control interface.
  • Utilizing the analog audio outputs, headphone or line driver outputs.
  • Managing the power supplies, clocks and grounds to minimize noise.

Proper PCB layout is critical to achieve good signal integrity and noise performance. The decoder IC datasheet will provide all required information to configure the system properly.

Conclusion

SPDIF is an important digital audio interface and SPDIF decoder ICs play a key role in recovering the original analog audio signal. Leading audio IC suppliers like Cirrus Logic, Wolfson and Texas Instruments offer excellent decoder options optimized for different applications and features. Engineers need to evaluate their design requirements like high-res support, jitter performance and target applications when selecting a suitable SPDIF decoder IC. Proper configuration and PCB layout is key to achieving maximum audio performance.

Frequently Asked Questions

What is the difference between optical and coaxial SPDIF inputs?

Optical SPDIF uses light to transmit the digital audio bits while coaxial SPDIF transmits the signal over an RCA cable. Optical connections provide better isolation from electrical noise but coaxial cables allow longer cable runs.

What sample rates does the SPDIF standard support?

The SPDIF standard supports sample rates from 32kHz to 192kHz including 44.1kHz and 48kHz commonly used for CDs and DATs.

Can DTS or Dolby Digital data streams be transmitted over SPDIF?

Yes, the SPDIF bitstream can contain compressed formats like Dolby Digital and DTS. The decoder IC regenerates the raw digital PCM data which is then passed to an external decoder chip.

What is the data format of the SPDIF bitstream?

SPDIF uses biphase mark coding (BMC) to encode the digital audio data and clock into a single serial data stream.

How do you isolate the SPDIF signal ground from noisy digital grounds?

Use optical isolation, ground plane splits and filters on SPDIF data lines. This prevents ground loop noise from coupling into the signal. Proper PCB layout is essential.