SD16_A Operation
22-4 SD16_A
22.2 SD16_A Operation
The SD16_A module is configured with user software. The setup and
operation of the SD16_A is discussed in the following sections.

22.2.1 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.

22.2.2 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.

22.2.3 Voltage Reference Generator

The SD16_A module has a built-in 1.2V reference. It 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.

22.2.4 Auto Power-Down

The SD16_A is designed for low power applications. When the SD16_A is not
actively converting, it is automatically disabled and automatically re-enabled
when a conversion is started. The reference is not automatically disabled, but
can be disabled by setting SD16REFON = 0. When the SD16_A or reference
are disabled, they consume no current.