Cirrus Logic AN134 User Manual

An134, Aes3 and s/pdif recommended transformers

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http://www.cirrus.com

AES3 and S/PDIF Recommended Transformers

Transformers are used in professional digital audio interfaces to provide common-mode noise and interference
rejection, high-frequency rejection, impedance-matching, isolation from ground loops, DC blocking, and short-cir-
cuit protection. Due to the specialized needs of this application, several manufacturers have designed transformers
specifically for AES3 and S/PDIF circuits.

The transformer used in the professional interface should be capable of operation from 3.6 to 24.6 MHz, which is
the audio data rate of 28 kHz to 192 kHz after biphase-mark encoding. Transformers used for digital audio should
also have low inter-winding capacitance. Inter-winding capacitance couples the primary and secondary windings,
degrading the isolation between the windings with increasing frequency. This energy appears in the form of com-
mon mode noise on the receive side ground and has the potential to degrade analog performance.

The companies listed in

Table 1

are a few manufacturers of digital audio transformers. Please contact these manu-

facturers directly for more detailed information

“References” on page 2

provides a list of transformer design and analysis papers

Cirrus Logic is unable to guarantee the performance of components manufactured by others.

MAY '05

AN134REV5

AN134

Table 1. Digital Audio Transformer Manufacturers

Manufacturer