STA680 datasheet(8/43 Pages) STMICROELECTRONICS

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System overview

STA680

8/43

2.1

HD Radio processing

The STA680 HD Radio Decoder does the processing of the IBOC signal. It receives a

complex digital signal from an AM/FM IF channel signal processor. The native sample rate is

744.1875 kS/s for FM and 46.51171875 kS/s for AM. However, other input sample rates are

acceptable because of the sample rate converter in the base-band Interface (BBI). These

include: 650 kS/s, 675 kS/s, 882 kS/s and 912 kS/s. If a base-band signal is provided that is

not at the native sample frequency of 744.1875 kHz it must be sample rate converted to this

rate. Sample rate conversion hardware is provided on-chip to support this. This feature

allows the STA680 to operate with various AM/FM front-ends.

The STA680is then responsible for detection, acquisition, and demodulation of the IBOC

signal. Such function is primarily implemented by the Vectra DSP core. The demodulated

signal is then passes to the Hi-Fi processor, for decoding, audio blending and handling of

data services. A digital 44.1 kHz decompressed audio is output via the Digital Audio

Interface.

The STA680 uses sophisticated algorithms to recover IBOC data even in the presence of

signal impairments including fading and a variety of other interferences.

To process the HD Radio stream STA680 requires a 4Mx16 external SDRAM (with up to

32Mx16 supported) for data storage.

2.2

Dual stream HD Radio processing

STA680 is capable to simultaneously demodulate two different HD Radio streams. This

unique feature enables the device to decode an HD Radio audio stream, in parallel with any

data service broadcasted by a different radio channel. The implementation of the dual

stream HD Radio processing requires that two AM/FM RF tuners are connected to the

STA680.

In a single channel implementation a single RF tuner is used. In such configuration STA680

is able to demodulate at the same time both the audio and the data associated with the radio

channel (i.e. 92.5 MHz or 102.5 MHz). This means that if the user sets the tuner 102.5 MHz,

he or she can listed to FM2 audio and receive traffic information broadcasted on that

channel. At the same time if the user tunes to another frequency (FM1), current traffic

information will be lost.

Figure 3.

Single channel application

FM1

Audio

FM1

News

FM 1

FM1

Audio

FM1

News

FM 1

FM2

Audio

FM2

Traffic

FM 2

FM2

Audio

FM2

Traffic

FM 2

92.5

102.5

MHz

FM1 News

FM1

Audio

FM1 News

FM1

Audio

FM2 Traffic

FM2

Audio

FM2 Traffic

FM2

Audio

Data received are bound to the selected Audio channel

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