PCM1795DB datasheet(36/58 Pages) TI

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APPLICATION CIRCUIT

I/V Section

Differential Section

PCM1795

SLES248 – MAY 2009 ........................................................................................................................................................................................................ www.ti.com

The design of the application circuit is very important in order to actually realize the high S/N ratio of which the

PCM1795 is capable, because noise and distortion that are generated in an application circuit are not negligible.

In the third-order, low-pass filter (LPF) circuit of Figure 52, the output level of 2.1 V RMS and 123-dB

signal-to-noise ratio is achieved.

Figure 53 shows a circuit for the DSD mode, which is a fourth-order LPF in order to reduce the out-of-band

noise.

The current of the PCM1795 on each of the output pins (IOUTL+, IOUTL–, IOUTR+, IOUTR–) is 4 mAPP at 0 dB

(full-scale). The voltage output level of the current-to-voltage (I/V) converter, VI, is given by Equation 2:

VI = 4 mAPP × RF

Where:

RF = feedback resistance of the I/V converter

An NE5534 operational amplifier is recommended for the I/V circuit to obtain the specified performance. Dynamic

performance such as the gain bandwidth, settling time, and slew rate of the operational amplifier affects the

audio dynamic performance of the I/V section.

The PCM1795 voltage outputs are followed by differential amplifier stages that sum the differential signals for

each channel, creating a single-ended I/V op-amp output. In addition, the differential amplifiers provide a

low-pass filter function.

The operational amplifier recommended for the differential circuit is the low-noise type.

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