ADC
AS1419
AS1419A
Differential Inputs
Full-Scale and Offset Adjustment
The AS1419 has a unique differential sample-and-hold
circuit that allows rail-to-rail inputs. The ADC will always
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 out-
put 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
input. For zero offset error, apply –152μV (i.e., – 0.5LSB) at
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
the AVDD or AVSS power supply voltages. Integral nonlinear-
ity errors (INL) and differential nonlinearity errors (DNL)
are
the
BZE is
independent of the common mode voltage, however,
bipolar zero error (BZE) will vary. The change in
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
+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
76dB with a
common mode of 2.5V or – 2.5V. Dif-
ferential 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.
(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.
Micross Components reserves the right to change products or specifications without notice.
AS1419 & AS1419A
Rev. 1.7 06/10
12
MICROSS [ MICROSS COMPONENTS ]
