SD16 Operation
21-4 SD16
21.2 SD16 Operation
The SD16 module is configured with user software. The setup and operation
of the SD16 is discussed in the following sections.

21.2.1 ADC Core

The analog-to-digital conversion is performed by a 1-bit, second-order
sigma-delta modulator. A single-bit comparator within the modulator quantizes
the input signal with the modulator frequency fM. The resulting 1-bit data
stream is averaged by the digital filter for the conversion result.

21.2.2 Analog Input Range and PGA

The full-scale input voltage range for each analog input pair is dependent on
the gain setting of the programmable gain amplifier of each channel. The
maximum full-scale range is ±VFSR where VFSR is defined by:
VFSR +VREFń2
GAINPGA
For a 1.2V reference, the maximum full-scale input range for a gain of 1 is:
"VFSR +1.2Vń2
1+" 0.6V
Refer to the device-specific data sheet for full-scale input specifications.

21.2.3 Voltage Reference Generator

The SD16 module has a built-in 1.2V reference that can be used for each SD16
channel and is enabled by the SD16REFON bit. When using the internal
reference an external 100nF capacitor connected from VREF to AVSS is
recommended to reduce noise. The internal reference voltage can be used
off-chip when SD16VMIDON = 1. The buffered output can provide up to 1mA
of drive. When using the internal reference off-chip, a 470nF capacitor
connected from VREF to AVSS is required. See device-specific data sheet for
parameters.
An external voltage reference can be applied to the VREF input when
SD16REFON and SD16VMIDON are both reset.

21.2.4 Auto Power-Down

The SD16 is designed for low power applications. When the SD16 is not
actively converting, it is automatically disabled and automatically re-enabled
when needed. The reference is not automatically disabled, but can be disabled
by setting SD16REFON = 0. When the SD16 or reference are disabled, they
consume no current.