PCM1609APT datasheet(28/43 Pages) TI

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ANALOG OUTPUTS

f − Frequency − Hz

−100

−80

−60

−40

−20

100

10M

G019

10k

100k

VCOM OUTPUT

–

VCOM

OPA337

µF

PCM1609A

S0054-04

BIAS +

PCM1609A

SLES145A – AUGUST 2005 – REVISED AUGUST 2006

The PCM1609A includes eight independent output channels, VOUT1 through VOUT8. These are unbalanced

outputs, each capable of driving 3.1 Vp-p typical into a 5-k

Ω ac load with V

CC = 5 V. The internal output

amplifiers for VOUT1 through VOUT8 are dc-biased to the common-mode (or bipolar zero) voltage, equal to VCC/2.

The output amplifiers include an RC continuous-time filter, which helps to reduce the out-of-band noise energy

present at the DAC outputs due to the noise-shaping characteristics of the PCM1609A delta-sigma DACs. The

frequency response of this filter is shown in Figure 28. By itself, this filter is not enough to attenuate the

out-of-band noise to an acceptable level for most applications. An external low-pass filter is required to provide

sufficient out-of-band noise rejection. Further discussion of DAC post-filter circuits is provided in the Application

Information section of this data sheet.

Figure 28. Output-Filter Frequency Response

One unbuffered, common-mode voltage output pin, VCOM (pin 15), is brought out for decoupling purposes. This

pin is nominally biased to a dc voltage level equal to VCC/2. If this pin is to be used to bias external circuitry, a

voltage follower is required for buffering purposes. Figure 29 shows an example of using the VCOM pin for

external biasing applications.

Figure 29. Biasing External Circuits Using the VCOM Pin

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