PCM1793

SLES076A − MARCH 2003 − REVISED JANUARY 2004

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21

Analog Gain of Balanced Amplifier

The DAC voltage outputs are followed by balanced amplifier stages, which sum the differential signals for each

channel, creating a single-ended voltage output. In addition, the balanced amplifiers provide a third-order

low-pass filter function, which band limits the audio output signal. The cutoff frequency and gain are determined

by external R and C component values. In this case, the cutoff frequency is 77 kHz with a gain of 1.83. The

output voltage for each channel is 5.9 Vp-p, or 2.1 V rms.

THEORY OF OPERATION

Analog

Voltage

Output

Digital

Input

24 Bit

8 fS

MSB

and

Lower 18 Bit

Upper

6 Bit

ICOB

Decoder

3rd-Order

5-Level

Sigma-Delta

Advanced

DWA

Current

Segment

DAC

0−4

Level

0−62

Level

0−66

I/V

Converter

Figure 29. Advanced Segment DAC With I/V Converter

The PCM1793 uses TI’s advanced segment DAC architecture to achieve excellent dynamic performance and

improved tolerance to clock jitter. The PCM1793 provides balanced voltage outputs.

Digital input data via the digital filter is separated into 6 upper bits and 18 lower bits. The 6 upper bits are converted

to inverted complementary offset binary (ICOB) code. The lower 18 bits, associated with the MSB, are processed

to the 1 LSB of the ICOB code converter. The data groups processed in the ICOB converter and third-order

delta-sigma modulator are summed together to an up-to-66-level digital code, and then processed by data-weighted

averaging (DWA) to reduce the noise produced by element mismatch. The data of up to 66 levels from the DWA is

converted to an analog output in the differential-current segment section.

This architecture has overcome the various drawbacks of conventional multibit processing and also achieves

excellent dynamic performance.