Test Parameter

Typical Description

Resolution

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

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

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)

(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)

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

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)

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)

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")

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")

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

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+)

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-)

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

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

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

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)

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)

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.

Test Parameter

Typical Description

Resolution

This is the number of bits that the DAC has. If a DAC has n bits, then its output analog signal span can be divided (or "resolved") into 2ⁿ states, each corresponding to its own digital input code.  The higher the number of bits, the better is the resolution of a DAC.

Voltage Reference Input Range

This indicates the minimum and maximum voltages that may be used as the DAC's external reference voltage.

Example of an Actual Spec:

0V min; Vdd max

Bipolar Zero Error or Midscale Error

This is the deviation of the actual analog output of the DAC from the ideal output of 0V when the 2's complement input code representing half-scale (all zeros) is loaded into the input register.

Example of an Actual Spec: +/- 30 mV typ.

Non-Linearity, Differential (DNL)

% of FSR

This is the difference between the actual or measured output change and the ideal output change for a digital input change of 1 LSB, i.e., for a transition between two adjacent codes.

Examples of Actual Specs:

+/- 1 LSB;

+/- 0.001% FSR typ.

Non-Linearity, Integral (INL)

or Relative Accuracy

This is the maximum deviation of the output from the straight line between the zero and full-scale points, excluding the effects of zero and full-scale errors.

Example of an Actual Spec:

+/-1 LSB typ.; +/- 4 LSB's max.

Analog Output Range or Full-Scale Range

This is the difference between the maximum and minimum analog output values that the DAC is specified to provide.

Example of Actual Spec:

-3V to +3V, Bipolar Mode

Logic Input Voltage, Vih

(Logic "1")

This is the minimum voltage that the digital inputs of the DAC are guaranteed to recognize as a Logic "1".

 Example of an Actual Spec: 2.4 V min.

Logic Input Voltage, Vil

(Logic "0")

This is the maximum voltage that the digital inputs of the DAC are guaranteed to recognize as a Logic "0".

Example of an Actual Spec: 0.8 V max.

Input Leakage Current, I_IL

This is maximum leakage current exhibited by a digital input at logic "0".

Example of an Actual Spec:

2 µA max. for Vil = 0.4 V.

Settling Time

This is the time required by the outputs of a DAC to reach and remain within a specified error band about its final value. This is measured from the digital input transition.

Examples of Actual Specs:

1.5 µsec typ. for a 6V step;

1.0 µsec typ. for a 1 LSB step;

Analog Positive Power Supply (+Vs)

This is the voltage range that can be used for the analog positive supply of the DAC.

Example of an Actual Spec:

+4.75V min.; +5.0V typ.; +13.2V max.

Analog Negative Power Supply (-Vs)

This is the voltage range that can be used for the analog negative supply of the DAC.

Example of an Actual Spec:

-13.2V min.; -5V typ.; -4.75V max.

Logic Positive Power Supply (+V_L)

This is the voltage range that can be used for the logic positive supply of the DAC.

Example of an Actual Spec:

+4.75V min.; +5.0V typ.; +13.2V max.

Logic Negative Power Supply (-V_L)

This is the voltage range that can be used for the logic negative supply of the DAC.

Example of an Actual Spec:

-13.2V min.; -5V typ.; -4.75V max.

Analog Output Impedance

This is the dynamic load presented by a DAC at its analog output. 

Example of an Actual Spec:

0.1 kW typ.

Gain Error or

Full-Scale Error

or %FSR

This indicates how closely the analog output of a DAC matches its ideal value at full scale and may be expressed in mV or as a % of the FSR. For many DAC's, the ideal maximum output voltage is Vref-1 LSB.

Example of an Actual Spec:

+/-1.22 mV

Signal-to-Noise Ratio (SNR)

This is the ratio of the amplitude of the analog output of the DAC when the output is set to full-scale to the amplitude of the output when it is set to zero.

Example of an Actual Spec:

107 dB min.; 110 dB typ. for 20 Hz-30 kHz

Total Harmonic Distortion (THD)

This is the ratio of the rms sum of the first few (2nd to 6th) harmonic components of the DAC output to the DAC output's fundamental value, usually expressed in dB.

Example of an Actual Spec:

-80 dB typ.