|
Test
Parameter |
Unit |
Typical Description |
|
Resolution |
Bits |
If an ADC has n
bits, then its resolution is 2n, which is the
number of states or codes that it can divide (or "resolve") the analog input into.
The higher the number of bits, the better is the resolution of the ADC,
and the more precise the representation of each state will be.
|
|
Unipolar Offset |
LSB |
The first
transition of an ADC should occur at an analog value that is 1/2 LSB above
the analog common. The deviation of the ADC's actual first
transition from this ideal level is known as the unipolar offset.
Example of an
Actual Spec: +/- 1 LSB max |
|
Bipolar Offset
or
Bipolar Zero Error |
LSB |
In the bipolar
mode, the major carry transition from '011111111111' to '100000000000'
should occur at an analog input value that is 1/2 LSB below the analog common.
The deviation of the actual value of this transition at 25 deg C from the
ideal level is known as the Bipolar Offset or Bipolar Zero Error.
Example of an
Actual Spec: +/- 1 LSB max |
|
Non-Linearity,
Differential (DNL) |
Bits
(with
no missing codes) |
In an ADC, code
transitions are 1 LSB apart. Maximum deviation from this ideal value
is known as differential non-linearity. It is often expressed in terms of
the number of bits guaranteed to have no missing codes.
Example of an
Actual Spec: 10 Bits min |
|
Non-Linearity, Integral
(INL) |
LSB |
The transfer
function of an ADC is a straight line from "zero" to "full scale".
The maximum deviation of a code from this straight line is the ADC's
integral non-linearity.
Example of an
Actual Spec: +/- 2
LSB's max |
|
Analog Input
Range or Full-Scale Range |
V |
This is the
difference between the maximum and minimum analog input values specified
for the ADC.
Examples of
Actual Specs:
0V to +10 V,
Unipolar Mode;
-5V to +5V,
Bipolar Mode |
|
Logic Output
(Current Sink) |
mA |
This is the amount of current
that the digital output of an ADC can sink when it is at Logic "0".
Example of an
Actual Spec:
3.2 mA when
Vout = 0.4V max |
|
Logic Output
(Current Source) |
mA |
This is the
amount of current that the digital output of an ADC can source when it is
at Logic "1".
Example of an
Actual Spec:
0.5 mA when
Vout = 2.4V max |
|
Logic Input
Voltage
(Logic "1") |
V |
This is the
minimum voltage that the digital inputs of the ADC are guaranteed to recognize as a
Logic "1".
Example
of an Actual Spec: 2.0 V min. |
|
Logic Input
Voltage
(Logic "0") |
V |
This is the
maximum voltage that the digital inputs of the ADC are guaranteed to recognize as a
Logic "0".
Example of an
Actual Spec: 0.8 V max. |
|
Conversion Time |
µsec |
This is
the time required by an ADC to make a complete measurement.
Example of an
Actual Spec:
15 µsec min.; 25 µsec typ.;
40 µsec max. |
|
+ Power Supply
(V+) |
V |
This is the
voltage range that can be used for the positive supply of the ADC.
Example of an
Actual Spec:
+4.5V
min.; +5.0V typ.; +7.0V
max. |
|
- Power Supply
(V-) |
V |
This is the
voltage range that can be used for the negative supply of the ADC.
Example of an
Actual Spec:
-12.0V
min.; -15V typ.; -16.5V
max. |
|
Analog Input
Impedance |
kW |
This is the
dynamic load presented by an ADC to its analog input source.
Example of an
Actual Spec:
3
kW
min.; 5
kW typ.;
7
kW
max. |
|
Gain Error |
LSB |
This is the
deviation of the actual difference between the first and last transitions
of an ADC from the ideal difference between its first and last
transitions. The last transition of the ADC should occur at an
analog input value that is 1.5 LSB's below the nominal full scale.
Example of an
Actual Spec:
+/- 2 LSB's typ.;
+/-4 LSB's
max. |
|
Power Supply
Rejection |
LSB |
This is the
maximum change in the full-scale transition point of the ADC due to a
deviation of its power supply voltage from its nominal value. This is
measured at full-scale.
Examples of
Actual Specs:
+/- 1 LSB max
for V+ = +4.5V to +5.5V;
+/- 1 LSB max
for V- = -12.6V to -11.4V |
|
Signal-to-Noise Ratio (SNR) |
dB |
This is the
ratio of the measured signal at the output of the ADC to the measured
noise. 'Signal' is the RMS magnitude of the fundamental signal while noise
is the RMS sum of all non-fundamental signals up to half the sampling
frequency, excluding the DC signal.
Example of an
Actual Spec:
44
dB typ. for Fin=1 MHz
and Ain=+/-1V |
|
Total Harmonic Distortion (THD) |
% or dB |
This is the
ratio of the rms sum of the first six harmonic components to the rms value
of a full-scale input signal, expressed either in % or dB. The aliased
component is used for input signals or harmonics that are above the
Nyquist frequency. The Nyquist frequency is the input signal frequency
that is 1/2 the sampling frequency of the ADC.
Examples of Actual Specs:
-88 dB typ.;
-80 dB max.
0.004%
typ.; 0.010% max. |
