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MCP3301_07 Datasheet, PDF (15/32 Pages) Microchip Technology – 13-Bit Differential Input, Low Power A/D Converter with SPI™ Serial Interface
5.0 DEFINITION OF TERMS
Bipolar Operation - This applies to either a differential
or single ended input configuration, where both positive
and negative codes are output from the A/D converter.
Full bipolar range includes all 8192 codes. For bipolar
operation on a single ended input signal, the A/D con-
verter must be configured to operate in pseudo differ-
ential mode.
Unipolar Operation - This applies to either a single
ended or differential input signal where only one side of
the device transfer is being used. This could be either
the positive or negative side, depending on which input
(IN+ or IN-) is being used for the DC bias. Full unipolar
operation is equivalent to a 12-bit converter.
Full Differential Operation - Applying a full differential
signal to both the IN(+) and IN(-) inputs is referred to as
full differential operation. This configuration is
described in Figure 3-4.
Pseudo-Differential Operation - Applying a single
ended signal to only one of the input channels with a
bipolar output is referred to as pseudo differential oper-
ation. To obtain a bipolar output from a single ended
input signal the inverting input of the A/D converter
must be biased above VSS. This operation is described
in Figure 3-5.
Integral Nonlinearity - The maximum deviation from a
straight line passing through the endpoints of the bipo-
lar transfer function is defined as the maximum integral
nonlinearity error. The endpoints of the transfer func-
tion are a point 1/2 LSB above the first code transition
(0x1000) and 1/2 LSB below the last code transition
(0x0FFF).
Differential Nonlinearity - The difference between two
measured adjacent code transitions and the 1 LSB
ideal is defined as differential nonlinearity.
Positive Gain Error - This is the deviation between the
last positive code transition (0x0FFF) and the ideal volt-
age level of VREF-1/2 LSB, after the bipolar offset error
has been adjusted out.
Negative Gain Error - This is the deviation between
the last negative code transition (0X1000) and the ideal
voltage level of -VREF-1/2 LSB, after the bipolar offset
error has been adjusted out.
Offset Error - This is the deviation between the first
positive code transition (0x0001) and the ideal 1/2 LSB
voltage level.
Acquisition Time - The acquisition time is defined as
the time during which the internal sample capacitor is
charging. This occurs for 1.5 clock cycles of the exter-
nal CLK as defined in Figure 7-2.
Conversion Time - The conversion time occurs imme-
diately after the acquisition time. During this time, suc-
cessive approximation of the input signal occurs as the
13-bit result is being calculated by the internal circuitry.
This occurs for 13 clock cycles of the external CLK as
defined in Figure 7-2.
© 2007 Microchip Technology Inc.
MCP3301
Signal to Noise Ratio - Signal to Noise Ratio (SNR) is
defined as the ratio of the signal to noise measured at
the output of the converter. The signal is defined as the
rms amplitude of the fundamental frequency of the
input signal. The noise value is dependant on the
device noise as well as the quantization error of the
converter and is directly affected by the number of bits
in the converter. The theoretical signal to noise ratio
limit based on quantization error only for an N-bit con-
verter is defined as:
EQUATION
SNR = (6.02N + 1.76)dB
For a 13-bit converter, the theoretical SNR limit is
80.02 dB.
Total Harmonic Distortion - Total Harmonic Distortion
(THD) is the ratio of the rms sum of the harmonics to
the fundamental, measured at the output of the con-
verter. For the MCP3301, it is defined using the first 9
harmonics, as shown in the following equation:
EQUATION
THD(-dB) = –20 log-----V----22---+-----V----32----+-----V----42----+-----.-.--.-.--.---+-----V---82----+-----V----92-
V12
Here V1 is the rms amplitude of the fundamental and V2
through V9 are the rms amplitudes of the second
through ninth harmonics.
Signal to Noise plus Distortion (SINAD) - Numeri-
cally defined, SINAD is the calculated combination of
SNR and THD. This number represents the dynamic
performance of the converter, including any harmonic
distortion.
EQUATION
SINAD(dB) = 20 log 10(SNR ⁄ 10) + 10–(THD ⁄ 10)
EffectIve Number of Bits - Effective Number of Bits
(ENOB) states the relative performance of the ADC in
terms of its resolution. This term is directly related to
SINAD by the following equation:
EQUATION
ENOB(N) = S----I--N-----A--6--D-.-0---2–-----1---.-7----6-
For SINAD performance of 78 dB, the effective number
of bits is 12.66.
Spurious Free Dynamic Range - Spurious Free
Dynamic Range (SFDR) is the ratio of the rms value of
the fundamental to the next largest component in
ADC’s output spectrum. This is, typically, the first har-
monic, but could also be a noise peak.
DS21700C-page 15