ADC
AS1419
AS1419A
Austin Semiconductor, Inc.
Full-Scale and Offset Adjustment
Differential Inputs
Figure 11a shows the ideal input/output characteristics
for the AS1419. The code transitions occur midway between
successive integer LSB values (i.e., –FS + 0.5LSB, – FS + 1.5LSB,
–FS + 2.5LSB,... FS – 1.5LSB, FS – 0.5LSB). The output is two’s
complement binary with 1LSB = FS – (– FS)/16384 = 5V/16384 =
305.2µV. In applications where absolute accuracy is important,
offset and full-scale errors can be adjusted to zero. Offset error
must be adjusted before full-scale error. Figure 11b shows the
extra components required for full-scale error adjustment. Zero
offset is achieved by adjusting the offset applied to the –AIN
The AS1419 has a unique differential sample-and-hold
circuit that allows rail-to-rail inputs. The ADC will always
convert the difference of +AIN – (–AIN) independent of the
common mode voltage (see Figure 11a). The common mode
rejection holds up to extremely high frequencies, see Figure
10a. The only requirement is that both inputs can not exceed
theAVDD orAVSS power supply voltages. Integral nonlinearity
errors (INL) and differential nonlinearity errors (DNL) are
independent of the common mode voltage, however, the
bipolar zero error (BZE) will vary. The change in BZE is
typically less than 0.1% of the common mode voltage. Dynamic
performance is also affected by the common mode voltage.
THD will degrade as the inputs approach either power supply
rail, from 86dB with a common mode of 0V to 76dB with a
common mode of 2.5Vor – 2.5V. Differential inputs allow greater
flexibility for accepting different input ranges. Figure 10b shows
a circuit that converts a 0V to 5V analog input signal with only
an additional buffer that is not in the signal path.
input. For zero offset error, apply –152µV (i.e., – 0.5LSB) at +AIN
and adjust the offset at the –AIN input until the output code
flickers between 0000 0000 0000 00 and 1111 1111 1111 11. For
full-scale adjustment, an input voltage of 2.499544V (FS/2 –
1.5LSBs) is applied to +AIN and R2 is adjusted until the output
code flickers between 0111 1111 1111 10 and 0111 1111 1111 11.
Austin Semiconductor, Inc. reserves the right to change products or specifications without notice.
AS1419 & AS1419A
Rev. 1.5 08/09
12
AUSTIN [ AUSTIN SEMICONDUCTOR ]
