that provides the comparator reference point. For CH1, the input to the SPI indicator
comes from U500-7.
U600-D acts as a unity gain inverter that creates a differential signal (+6dB gain) to
feed the attenuator for either the TI DSP’s ADC (XLS1000) or Cirrus Codec
(XLS1500, 2000, 2500). For the XLS1000, R618-619, R621-623 form a voltage
divider and bias network into the TI DSP (CH2±_DSP_AD). In the case of the
XLS1500 – 2500, R613-614, R617, R620 form the voltage divider and bias network
into the Cirrus codec (CH2±_AD).
As you can see, the major difference between the XLS1000 and XLS1500 – 2500
APM’s resides in the use of an external Cirrus Codec (U702) for the larger amplifiers.
This results in ~4dB better S/N, but at an additional cost of $2.
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