STA680 datasheet(26/43 Pages) STMICROELECTRONICS

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Digital I/O and memory interfaces

STA680

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5.2

Tuner interface

The STA680 provides two digital base-band interfaces, named BBI1 and BBI2, through

which the demodulated IBOC signals can enter the HD Radio decoder. The base-band

Tuner accepts the analog signal from the RF Tuner, samples it, performs down conversion

and filtering, and sends the zero-IF signal across a base-band interface (BBI) to the

STA680.

Using two interfaces the STA680 is able to decode two channels at the same time, allowing

the implementation of features such as the background scanning of HD Radio channels in

search of traffic or weather information.

The BBI consists of four-wires, 16 bit wide I and Q data and two clocks. MSB is always

transmitted first. All signals are assumed to be zero-if.

The native rate for FM is 744.1875 kS/s and for AM it is 46.51171875 kS/s. Sample rates of

650 kS/s, 675 kS/s, 882 kS/s and 912 kS/s are acceptable via the use of a sample rate

converter.

BBI2 is similar to BBI1 except BBI2 doesn’t have center filter so it is intended to be used for

digital modulated signal only. For pin description refers to the Table 5.

The data stream of the base-band interface varies depending on the mode selected.

Split mode splits I and Q data onto the BB1_I and BB1_Q pins, respectively. The rising and

falling edges of BB1_WS mark the beginning of each I and Q pair.

Multiplexed mode places the I and Q data onto the BB1_I data pin. The falling edge of

BB1_WS marks the start of the I data and the rising edge marks the start of Q data.

AFE mode uses a single clock pulse on BB1_WS to indicate the start of I data followed by Q

data using the BB1_I pin only.

Figure 9 show signals waveform for the three modes.

Table 6.

Base-band interfaces pin list

Pin name

Designation

Type

Drive

BB1_WS

Secondary base band interface word strobe

BB1_BCK

Primary base-band interface bit clock

BB1_I

Primary base-band interface serial I data

BB1_Q

Primary base-band interface serial Q data

BB2_WS

Secondary base-band interface word strobe

BB2_BCK

Secondary base-band interface bit clock

BB2_I

Secondary base-band interface serial I data

BB2_Q

Secondary base-band interface serial Q data

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