CS5378 datasheet(60/88 Pages) CIRRUS

60 / 88 page

CS5378

DS639F2

17. TEST BIT STREAM GENERATOR

The CS5378 test bit stream (TBS) generator creates

sine wave

∆Σ bit stream data to drive an external

test DAC. The TBS digital output can also be in-

ternally connected to the MDATA inputs for loop-

back testing of the digital filter.

17.1 Pin Descriptions

TBSDATA - Pin 8

Test bit stream 1-bit

∆Σ data output.

MCLK - Pin 11

Test bit stream clock output.

17.2 TBS Architecture

The test bit stream generator consists of a data in-

terpolator and a digital

∆Σ modulator. It receives

periodic 24-bit data from the digital filter to create

a 1-bit

∆Σ data output on the TBSDATA pin.

The TBS input data from the digital filter is scaled

by the TBSGAIN register (0x2B). Maximum sta-

ble amplitude is 0x04FFFF, with 0x04B000 ap-

proximately full scale for the CS5373A test DAC.

The full scale 1-bit

∆Σ output from the TBS gener-

ator is defined as 25% minimum and 75% maxi-

mum one’s density.

17.3 TBS Configuration

Configuration options for the TBS generator are set

through the TBSCFG register (0x2A). Gain scal-

ing of the TBS generator output is set by the TB-

SGAIN register (0x2B).

Interpolation Factor - INTP[7:0]

Selects how many times the interpolator uses a data

point when generating the output bit stream. Inter-

polation is zero based and represents one greater

than the programmed register value.

Output Rate - RATE[2:0]

Selects the TBSDATA output rate.

Synchronization - TSYNC

Enables synchronization of the TBS output phase

to the MSYNC signal.

Loopback - LOOP

Enables digital loopback from the TBS output to

the MDATA inputs.

Run - RUN

Enables the test bit stream generator.

Digital

∆Σ Modulator

24-bit

1-bit

TBSDATA

Digital Filter

TBSGAIN Register

24-bit

Figure 36. Test Bit Stream Generator Block Diagram

Data Bus

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