CS5378 datasheet(60/86 Pages) CIRRUS

60 / 86 page

CS5378

DS639F1

17. TEST BIT STREAM GENERATOR

The CS5378 test bit stream (TBS) generator creates

sine wave or impulse

∆Σ bit stream data to drive an

external test DAC. The TBS digital output can also

be internally connected to the MDATA inputs for

loopback 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 CS4373 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.

Operational Mode - TMODE

Selects between sine wave or impulse output mode.

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.

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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