ADC121S101/ADC101S101/ADC081S101
1MSPS, 12-/10-/8-Bit A/D Converters in SOT-23
General Description
The ADC121S101, ADC101S101, and ADC081S101 are low
power, monolithic CMOS 12-, 10- and 8-bit analog-to-digital
converters that operate at 1 MSPS. Each device is based on
a successive approximation register architecture with inter-
nal track-and-hold. The serial interface is compatible with
several standards, such as SPI, QSPI, MICROWIRE,
and many common DSP serial interfaces.
The ADC121S101/101S101/081S101 uses the supply volt-
age as a reference. This enables the devices to operate with
a full-scale input range of 0 to V
DD
. The conversion rate is
determined from the serial clock (SCLK) speed. These con-
verters offer a shutdown mode, which can be used to trade
throughput for power consumption. The ADC121S101/
101S101/081S101 is operated with a single supply that can
range from +2.7V to +5.25V. Normal power consumption
during continuous conversion, using a +3V or +5V supply, is
2 mW or 10 mW respectively. The power down feature,
which is enabled by a chip select (CS) pin, reduces the
power consumption to under 5 µW using a +5V supply. All
three converters are available in a 6-lead SOT-23 package,
which provides an extremely small footprint for applications
where space is a critical consideration. These products are
designed for operation over the automotive/extended indus-
trial temperature range of −40˚C to +125˚C.
Features
nVariable power management
nPackaged in 6-lead SOT-23
nPower supply used as reference
nSingle +2.7V to +5.25V supply operation
nSPI/QSPI/MICROWIRE/DSP compatible
Key Specifications
nResolution with no Missing Codes 12/10/8 bits
nConversion Rate 1 MSPS
nDNL +0.5, -0.3 LSB (typ)
nINL ±0.4 LSB (typ)
nPower Consumption
3V Supply 2 mW (typ)
5V Supply 10 mW (typ)
Applications
nAutomotive Navigation
nFA/ATM Equipment
nPortable Systems
nMedical Instruments
nMobile Communications
nInstrumentation and Control Systems
Connection Diagram
20110201
MICROWIREis a trademark of National Semiconductor Corporation.
TRI-STATE®is a trademark of National Semiconductor Corporation.
QSPIand SPIare trademarks of Motorola, Inc.
June 2004
ADC121S101/ADC101S101/ADC081S101 1MSPS, 12-/10-/8-Bit A/D Converters in SOT-23
© 2004 National Semiconductor Corporation DS201102 www.national.com
Ordering Information
Order Code Temperature Range Description Top Mark
ADC121S101CIMF −40˚C to +125˚C 6-Lead SOT-23 Package X01C
ADC101S101CIMF −40˚C to +85˚C 6-Lead SOT-23 Package X02C
ADC081S101CIMF −40˚C to +85˚C 6-Lead SOT-23 Package X03C
ADC121S101CIMFX −40˚C to +125˚C 6-Lead SOT-23 Package, Tape & Reel X01C
ADC101S101CIMFX −40˚C to +85˚C 6-Lead SOT-23 Package, Tape & Reel X02C
ADC081S101CIMFX −40˚C to +85˚C 6-Lead SOT-23 Package, Tape & Reel X03C
Pin Descriptions
Pin No. Symbol Description
ANALOG I/O
3V
IN
Analog input. This signal can range from 0V to V
DD
.
DIGITAL I/O
4 SCLK
Digital clock input. The range of frequencies for this input is 10 kHz to 20 MHz, with
guaranteed performance at 20 MHz. This clock directly controls the conversion and readout
processes.
5 SDATA Digital data output. The output words are clocked out of this pin by the SCLK pin.
6CS
Chip select. A conversion process begins on the falling edge of CS.
POWER SUPPLY
1V
DD
Positive supply pin. These pins should be connected to a quiet +2.7V to +5.25V source and
bypassed to GND with 0.1 µF and 1 µF monolithic capacitors located within 1 cm of the
power pin. The ADC121S101/101S101/081S101 uses this power supply as a reference, so it
should be thoroughly bypassed.
2 GND The ground return for the supply.
Block Diagram
20110218
ADC121S101/ADC101S101/ADC081S101
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Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage V
DD
−0.3V to +6.5V
Voltage on Any Analog Pin to GND −0.3V to V
DD
+0.3V
Voltage on Any Digital Pin to GND -0.3V to 6.5V
Input Current at Any Pin (Note 3) ±10 mA
ESD Susceptibility
Human Body Model
Machine Model
3500V
200V
Soldering Temperature, Infrared,
10 seconds 215˚C
Junction Temperature +150˚C
Storage Temperature −65˚C to +150˚C
Operating Ratings
Operating Temperature Range T
MIN
= −40˚C T
A
T
MAX
= +125˚C
V
DD
Supply Voltage +2.7V to +5.25V
Digital Input Pins Voltage Range
(Note 4) +2.7V to +5.25V
Package Thermal Resistance
Package θ
JA
6-Lead SOT-23 265˚C / W
ADC121S101/ADC101S101/ADC081S101 Specifications(Note 2)
ADC121S101 Converter Electrical Characteristics
The following specifications apply for V
DD
= +2.7V to 5.25V, f
SCLK
= 20 MHz, f
SAMPLE
= 1 MSPS unless otherwise noted. Bold-
face limits apply for T
A
= −40˚C to +85˚C: all other limits T
A
= 25˚C, unless otherwise noted.
Symbol Parameter Conditions Typical Limits Units
STATIC CONVERTER CHARACTERISTICS (V
DD
= 2.7V to 3.6V)
Resolution with No Missing Codes −40˚C T
A
125˚C 12 Bits
INL Integral Non-Linearity
−40˚C T
A
85˚C ±0.4 ±1LSB (max)
T
A
= 125˚C +1
-1.1
LSB (min)
LSB (max)
DNL Differential Non-Linearity −40˚C T
A
85˚C +0.5
-0.3
+1
-0.9
LSB (max)
LSB (min)
T
A
= 125˚C ±1 LSB (max)
V
OFF
Offset Error −40˚C T
A
125˚C ±0.1 ±1.2 LSB (max)
GE Gain Error −40˚C T
A
125˚C ±0.2 ±1.2 LSB (max)
DYNAMIC CONVERTER CHARACTERISTICS (f
IN
= 100 kHz, -0.02 dBFS sine wave unless otherwise noted)
SINAD Signal-to-Noise Plus Distortion Ratio −40˚C T
A
125˚C 72 70 dB (min)
SNR Signal-to-Noise Ratio −40˚C T
A
85˚C 72.5 70.8 dB (min)
T
A
= 125˚C 70.6 dB (min)
THD Total Harmonic Distortion -80 dB
SFDR Spurious-Free Dynamic Range 82 dB
IMD
Intermodulation Distortion, Second
Order Terms f
a
= 103.5 kHz, f
b
= 113.5 kHz -78 dB
Intermodulation Distortion, Third
Order Terms f
a
= 103.5 kHz, f
b
= 113.5 kHz -78 dB
FPBW -3 dB Full Power Bandwidth +5V Supply 11 MHz
+3V Supply 8 MHz
POWER SUPPLY CHARACTERISTICS
V
DD
Supply Voltage −40˚C T
A
125˚C 2.7 V (min)
5.25 V (max)
ADC121S101/ADC101S101/ADC081S101
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ADC121S101/ADC101S101/ADC081S101 Specifications(Note 2) (Continued)
ADC121S101 Converter Electrical Characteristics (Continued)
The following specifications apply for V
DD
= +2.7V to 5.25V, f
SCLK
= 20 MHz, f
SAMPLE
= 1 MSPS unless otherwise noted. Bold-
face limits apply for T
A
= −40˚C to +85˚C: all other limits T
A
= 25˚C, unless otherwise noted.
Symbol Parameter Conditions Typical Limits Units
POWER SUPPLY CHARACTERISTICS
I
DD
Normal Mode (Static)
V
DD
= +4.75V to +5.25V,
SCLK On or Off 2mA
V
DD
= +2.7V to +3.6V,
SCLK On or Off 1mA
Normal Mode (Operational)
V
DD
= +4.75V to +5.25V,
f
SAMPLE
= 1 MSPS 2.0 3.5 mA (max)
V
DD
= +2.7V to +3.6V,
f
SAMPLE
= 1 MSPS 0.6 1.6 mA (max)
Shutdown Mode V
DD
= +5V, SCLK Off 0.5 µA
V
DD
= +5V, SCLK On 60 µA
P
D
Power Consumption, Normal Mode
(Operational)
V
DD
= +5V, f
SAMPLE
= 1 MSPS 10 17.5 mW (max)
V
DD
= +3V, f
SAMPLE
= 1 MSPS 2 4.8 mW (max)
Power Consumption, Shutdown Mode V
DD
= +5V, SCLK Off 2.5 µW
V
DD
= +3V, SCLK Off 1.5 µW
ANALOG INPUT CHARACTERISTICS
V
IN
Input Range 0 to V
DD
V
I
DCL
DC Leakage Current ±1µA (max)
C
INA
Input Capacitance 30 pF
DIGITAL INPUT CHARACTERISTICS
V
IH
Input High Voltage 2.4 V (min)
V
IL
Input Low Voltage V
DD
= +5V 0.8 V (max)
V
DD
= +3V 0.4 V (max)
I
IN
Input Current V
IN
=0VorV
DD
±10 nA ±1µA (max)
C
IND
Input Capacitance 2 4pF (max)
DIGITAL OUTPUT CHARACTERISTICS
V
OH
Output High Voltage I
SOURCE
= 200 µA,
V
DD
= +2.7V to +5.25V V
DD
−0.2 V (min)
V
OL
Output Low Voltage I
SINK
= 200 µA 0.4 V (max)
I
OL
TRI-STATE Leakage Current ±10 µA (max)
C
OUT
TRI-STATE Output Capacitance 2 4pF (max)
Output Coding Straight (Natural) Binary
AC ELECTRICAL CHARACTERISTICS
f
SCLK
Clock Frequency 20 MHz (max)
DC SCLK Duty Cycle 40
60
% (min)
% (max)
t
TH
Track/Hold Acquisition Time 400 ns (max)
f
RATE
Throughput Rate See Serial Interface Section 1MSPS
(max)
t
AD
Aperture Delay 3 ns
t
AJ
Aperture Jitter 30 ps
ADC121S101/ADC101S101/ADC081S101
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ADC121S101/ADC101S101/ADC081S101 Specifications(Note 2) (Continued)
ADC101S101 Converter Electrical Characteristics
The following specifications apply for V
DD
= +2.7V to 5.25V, f
SCLK
= 20 MHz, f
SAMPLE
= 1 MSPS unless otherwise noted. Bold-
face limits apply for T
A
= −40˚C to +85˚C: all other limits T
A
= 25˚C, unless otherwise noted.
Symbol Parameter Conditions Typical Limits Units
STATIC CONVERTER CHARACTERISTICS
Resolution with No Missing Codes 10 Bits
INL Integral Non-Linearity ±0.2 ±0.7 LSB (max)
DNL Differential Non-Linearity +0.3
-0.2 ±0.7 LSB (max)
LSB (max)
V
OFF
Offset Error ±0.1 ±0.7 LSB (max)
GE Gain Error ±0.2 ±1LSB (max)
DYNAMIC CONVERTER CHARACTERISTICS
SINAD Signal-to-Noise Plus Distortion Ratio f
IN
= 100 kHz 61.7 61 dBFS (min)
SNR Signal-to-Noise Ratio f
IN
= 100 kHz 62 dB
THD Total Harmonic Distortion f
IN
= 100 kHz -77 -73 dB (max)
SFDR Spurious-Free Dynamic Range f
IN
= 100 kHz 78 74 dB (min)
IMD
Intermodulation Distortion, Second
Order Terms f
a
= 103.5 kHz, f
b
= 113.5 kHz -78 dB
Intermodulation Distortion, Third
Order Terms f
a
= 103.5 kHz, f
b
= 113.5 kHz -78 dB
FPBW -3 dB Full Power Bandwidth +5V Supply 11 MHz
+3V Supply 8 MHz
POWER SUPPLY CHARACTERISTICS
V
DD
Supply Voltage 2.7
5.25
V (min)
V (max)
I
DD
Normal Mode (Static)
V
DD
= +4.75V to +5.25V,
SCLK On or Off 2mA
V
DD
= +2.7V to +3.6V,
SCLK On or Off 1mA
Normal Mode (Operational)
V
DD
= +4.75V to +5.25V,
f
SAMPLE
= 1 MSPS 2.0 3.5 mA (max)
V
DD
= +2.7V to +3.6V,
f
SAMPLE
= 1 MSPS 0.6 1.6 mA (max)
Shutdown Mode V
DD
= +5V, SCLK Off 0.5 µA (max)
V
DD
= +5V, SCLK On 60 µA (max)
P
D
Power Consumption, Normal Mode
(Operational)
V
DD
= +5V, f
SAMPLE
= 1 MSPS 10 17.5 mW (max)
V
DD
= +3V, f
SAMPLE
= 1 MSPS 2 4.8 mW (max)
Power Consumption, Shutdown Mode V
DD
= +5V, SCLK Off 2.5 µW (max)
V
DD
= +3V, SCLK Off 1.5 µW (max)
ANALOG INPUT CHARACTERISTICS
V
IN
Input Range 0 to V
DD
V
I
DCL
DC Leakage Current ±1µA (max)
C
INA
Input Capacitance 30 pF
DIGITAL INPUT CHARACTERISTICS
V
IH
Input High Voltage 2.4 V (min)
V
IL
Input Low Voltage V
DD
= +5V 0.8 V (max)
V
DD
= +3V 0.4 V (max)
I
IN
Input Current V
IN
=0VorV
DD
±10 nA ±1µA (max)
C
IND
Input Capacitance 2 4pF (max)
ADC121S101/ADC101S101/ADC081S101
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ADC121S101/ADC101S101/ADC081S101 Specifications(Note 2) (Continued)
ADC101S101 Converter Electrical Characteristics (Continued)
The following specifications apply for V
DD
= +2.7V to 5.25V, f
SCLK
= 20 MHz, f
SAMPLE
= 1 MSPS unless otherwise noted. Bold-
face limits apply for T
A
= −40˚C to +85˚C: all other limits T
A
= 25˚C, unless otherwise noted.
Symbol Parameter Conditions Typical Limits Units
DIGITAL OUTPUT CHARACTERISTICS
V
OH
Output High Voltage I
SOURCE
= 200 µA,
V
DD
= +2.7V to +5.25V V
DD
−0.2 V (min)
V
OL
Output Low Voltage I
SINK
= 200 µA 0.4 V (max)
I
OL
TRI-STATE Leakage Current ±10 µA (max)
C
OUT
TRI-STATE Output Capacitance 2 4pF (max)
Output Coding Straight (Natural) Binary
AC ELECTRICAL CHARACTERISTICS
f
SCLK
Clock Frequency 20 MHz (max)
DC SCLK Duty Cycle 40
60
% (min)
% (max)
t
TH
Track/Hold Acquisition Time 400 ns (max)
f
RATE
Throughput Rate See Serial Interface Section 1MSPS
(max)
t
AD
Aperture Delay 3 ns
t
AJ
Aperture Jitter 30 ps
ADC121S101/ADC101S101/ADC081S101
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ADC121S101/ADC101S101/ADC081S101 Specifications(Note 2) (Continued)
ADC081S101 Converter Electrical Characteristics
The following specifications apply for V
DD
= +2.7V to 5.25V, f
SCLK
= 20 MHz, f
SAMPLE
= 1 MSPS unless otherwise noted. Bold-
face limits apply for T
A
= −40˚C to +85˚C: all other limits T
A
= 25˚C, unless otherwise noted.
Symbol Parameter Conditions Typical Limits Units
STATIC CONVERTER CHARACTERISTICS
Resolution with No Missing Codes 8Bits
INL Integral Non-Linearity ±0.05 ±0.3 LSB (max)
DNL Differential Non-Linearity ±0.07 ±0.3 LSB (max)
V
OFF
Offset Error ±0.03 ±0.3 LSB (max)
GE Gain Error ±0.08 ±0.4 LSB (max)
Total Unadjusted Error ±0.07 ±0.3 LSB (max)
DYNAMIC CONVERTER CHARACTERISTICS
SINAD Signal-to-Noise Plus Distortion Ratio f
IN
= 100 kHz 49.7 49 dB (min)
SNR Signal-to-Noise Ratio f
IN
= 100 kHz 49.7 dB
THD Total Harmonic Distortion f
IN
= 100 kHz -77 -65 dB (max)
SFDR Spurious-Free Dynamic Range f
IN
= 100 kHz 69 65 dB (min)
IMD
Intermodulation Distortion, Second
Order Terms f
a
= 103.5 kHz, f
b
= 113.5 kHz -68 dB
Intermodulation Distortion, Third
Order Terms f
a
= 103.5 kHz, f
b
= 113.5 kHz -68 dB
FPBW -3 dB Full Power Bandwidth +5V Supply 11 MHz
+3V Supply 8 MHz
POWER SUPPLY CHARACTERISTICS
V
DD
Supply Voltage 2.7
5.25
V (min)
V (max)
I
DD
Normal Mode (Static)
V
DD
= +4.75V to +5.25V,
SCLK On or Off 2mA
V
DD
= +2.7V to +3.6V,
SCLK On or Off 1mA
Normal Mode (Operational)
V
DD
= +4.75V to +5.25V,
f
SAMPLE
= 1 MSPS 2.0 3.5 mA (max)
V
DD
= +2.7V to +3.6V,
f
SAMPLE
= 1 MSPS 0.6 1.6 mA (max)
Shutdown Mode V
DD
= +5V, SCLK Off 0.5 µA (max)
V
DD
= +5V, SCLK On 60 µA (max)
P
D
Power Consumption, Normal Mode
(Operational)
V
DD
= +5V, f
SAMPLE
= 1 MSPS 10 17.5 mW (max)
V
DD
= +3V, f
SAMPLE
= 1 MSPS 2 4.8 mW (max)
Power Consumption= Shutdown
Mode
V
DD
= +5V, SCLK Off 2.5 µW (max)
V
DD
= +3V, SCLK Off 1.5 µW (max)
ANALOG INPUT CHARACTERISTICS
V
IN
Input Range 0 to V
DD
V
I
DCL
DC Leakage Current ±1µA (max)
C
INA
Input Capacitance 30 pF
DIGITAL INPUT CHARACTERISTICS
V
IH
Input High Voltage 2.4 V (min)
V
IL
Input Low Voltage V
DD
= +5V 0.8 V (max)
V
DD
= +3V 0.4 V (max)
I
IN
Digital Input Current V
IN
=0VorV
DD
±10 nA ±1µA (max)
C
IND
Input Capacitance 2 4pF(max)
ADC121S101/ADC101S101/ADC081S101
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ADC121S101/ADC101S101/ADC081S101 Specifications(Note 2) (Continued)
ADC081S101 Converter Electrical Characteristics (Continued)
The following specifications apply for V
DD
= +2.7V to 5.25V, f
SCLK
= 20 MHz, f
SAMPLE
= 1 MSPS unless otherwise noted. Bold-
face limits apply for T
A
= −40˚C to +85˚C: all other limits T
A
= 25˚C, unless otherwise noted.
Symbol Parameter Conditions Typical Limits Units
DIGITAL OUTPUT CHARACTERISTICS
V
OH
Output High Voltage I
SOURCE
= 200 µA,
V
DD
= +2.7V to +5.25V V
DD
−0.2 V (min)
V
OL
Output Low Voltage I
SINK
= 200 µA 0.4 V (max)
I
OL
TRI-STATE Leakage Current ±10 µA (max)
C
OUT
TRI-STATE Output Capacitance 2 4pF (max)
Output Coding Straight (Natural) Binary
AC ELECTRICAL CHARACTERISTICS
f
SCLK
Clock Frequency 20 MHz (max)
DC SCLK Duty Cycle 40
60
% (min)
% (max)
t
TH
Track/Hold Acquisition Time 400 ns (max)
f
RATE
Throughput Rate See Applications Section 1MSPS (min)
t
AD
Aperture Delay 3 ns
t
AJ
Aperture Jitter 30 ps
Note 1: Absolute maximum ratings are limiting values, to be applied individually, and beyond which the serviceability of the circuit may be impaired. Functional
operability under any of these conditions is not implied. Exposure to maximum ratings for extended periods may affect device reliability.
Note 2: Data sheet min/max specification limits are guaranteed by design, test, or statistical analysis.
Note 3: Except power supply pins.
Note 4: Independent of supply voltage.
ADC121S101/ADC101S101/ADC081S101
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Timing Test Circuit
20110208
ADC121S101/ADC101S101/ADC081S101 Timing Specifications
The following specifications apply for V
DD
= +2.7V to 5.25V, f
SCLK
= 20 MHz, Boldface limits apply for T
A
= −40˚C to +85˚C:
all other limits T
A
= 25˚C, unless otherwise noted. (Note 9)
Symbol Parameter Conditions Typical Limits Units
t
CONVERT
16xt
SCLK
t
QUIET
(Note 5) 50 ns (min)
t
1
Minimum CS Pulse Width 10 ns (min)
t
2
CS to SCLK Setup Time 10 ns (min)
t
3
Delay from CS Until SDATA
TRI-STATE®Disabled (Note 6) 20 ns (max)
t
4
Data Access Time after SCLK Falling
Edge(Note 7)
V
DD
= +2.7 to +3.6 40 ns (max)
V
DD
= +4.75 to +5.25 20 ns (max)
t
5
SCLK Low Pulse Width 0.4 x
t
SCLK
ns (min)
t
6
SCLK High Pulse Width 0.4 x
t
SCLK
ns (min)
t
7
SCLK to Data Valid Hold Time V
DD
= +2.7 to +3.6 7ns (min)
V
DD
= +4.75 to +5.25 5ns (min)
t
8
SCLK Falling Edge to SDATA High
Impedance (Note 8)
V
DD
= +2.7 to +3.6 25 ns (max)
6ns (min)
V
DD
= +4.75 to +5.25 25 ns (max)
5ns (min)
t
POWER-UP
Power-Up Time from Full
Power-Down s
Note 5: Minimum Quiet Time Required Between Bus Relinquish and Start of Next Conversion
Note 6: Measured with the load circuit shown above, and defined as the time taken by the output to cross 1.0V.
Note 7: Measured with the load circuit shown above, and defined as the time taken by the output to cross 1.0V or 2.0V.
Note 8: t8is derived from the time taken by the outputs to change by 0.5V with the loading circuit shown above. The measured number is then adjusted to remove
the effects of charging or discharging the 25pF capacitor. This means t8is the true bus relinquish time, independent of the bus loading.
Note 9: All input signals are specified as tr=t
f= 5 ns (10% to 90% VDD) and timed from 1.6V.
ADC121S101/ADC101S101/ADC081S101
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Specification Definitions
APERTURE DELAY is the time after the falling edge of CS
to when the input signal is acquired or held for conversion.
APERTURE JITTER (APERTURE UNCERTAINTY) is the
variation in aperture delay from sample to sample. Aperture
jitter manifests itself as noise in the output.
DIFFERENTIAL NON-LINEARITY (DNL) is the measure of
the maximum deviation from the ideal step size of 1 LSB.
DUTY CYCLE is the ratio of the time that a repetitive digital
waveform is high to the total time of one period. The speci-
fication here refers to the SCLK.
EFFECTIVE NUMBER OF BITS (ENOB, or EFFECTIVE
BITS) is another method of specifying Signal-to-Noise and
Distortion or SINAD. ENOB is defined as (SINAD - 1.76) /
6.02 and says that the converter is equivalent to a perfect
ADC of this (ENOB) number of bits.
FULL POWER BANDWIDTH is a measure of the frequency
at which the reconstructed output fundamental drops 3 dB
below its low frequency value for a full scale input.
GAIN ERROR is the deviation of the last code transition
(111...110) to (111...111) from the ideal (V
REF
- 1.5 LSB for
ADC121S101 and ADC101S101, V
REF
- 1 LSB for
ADC081S101), after adjusting for offset error.
INTEGRAL NON-LINEARITY (INL) is a measure of the
deviation of each individual code from a line drawn from
negative full scale (
1
2
LSB below the first code transition)
through positive full scale (
1
2
LSB above the last code
transition). The deviation of any given code from this straight
line is measured from the center of that code value.
INTERMODULATION DISTORTION (IMD) is the creation of
additional spectral components as a result of two sinusoidal
frequencies being applied to the ADC input at the same time.
It is defined as the ratio of the power in the either the two
second order or all four third order intermodulation products
to the sum of the power in both of the original frequencies.
IMD is usually expressed in dBFS.
MISSING CODES are those output codes that will never
appear at the ADC outputs. The ADC121S101/101S101/
081S101 is guaranteed not to have any missing codes.
OFFSET ERROR is the deviation of the first code transition
(000...000) to (000...001) from the ideal (i.e. GND + 0.5 LSB
for the ADC121S101 and ADC101S101, and GND+1LSB
for the ADC081S101).
SIGNAL TO NOISE RATIO (SNR) is the ratio, expressed in
dB, of the rms value of the input signal to the rms value of the
sum of all other spectral components below one-half the
sampling frequency, not including harmonics or dc.
SIGNAL TO NOISE PLUS DISTORTION (S/N+D or SINAD)
Is the ratio, expressed in dB, of the rms value of the input
signal to the rms value of all of the other spectral compo-
nents below half the clock frequency, including harmonics
but excluding dc.
SPURIOUS FREE DYNAMIC RANGE (SFDR) is the differ-
ence, expressed in dB, between the rms values of the input
signal and the peak spurious signal, where a spurious signal
is any signal present in the output spectrum that is not
present at the input.
TOTAL HARMONIC DISTORTION (THD) is the ratio, ex-
pressed in dBc, of the rms total of the first five harmonic
levels at the output to the level of the fundamental at the
output. THD is calculated as
where Af
1
is the RMS power of the fundamental (output)
frequency and Af
2
through Af
6
are the RMS power in the first
5 harmonic frequencies.
TOTAL UNADJUSTED ERROR is the worst deviation found
from the ideal transfer function. As such, it is a comprehen-
sive specification which includes full scale error, linearity
error, and offset error.
ADC121S101/ADC101S101/ADC081S101
www.national.com 10
Timing Diagrams
20110202
FIGURE 1. ADC121S101 Serial Interface Timing Diagram
20110203
FIGURE 2. ADC101S101 Serial Interface Timing Diagram
ADC121S101/ADC101S101/ADC081S101
www.national.com11
Timing Diagrams (Continued)
20110204
FIGURE 3. ADC081S101 Serial Interface Timing Diagram
ADC121S101/ADC101S101/ADC081S101
www.national.com 12
Typical Performance Characteristics T
A
= +25˚C, V
DD
= 3V, f
SAMPLE
= 1 MSPS, f
SCLK
= 20 MHz,
f
IN
= 100 kHz unless otherwise stated.
ADC121S101
ADC121S101 DNL ADC121S101 INL
20110206 20110205
ADC121S101 Spectral Response @100 kHz Input ADC121S101 THD vs. Source Impedance
20110207 20110250
ADC121S101 THD vs. Input Frequency, 600 kSPS ADC121S101 THD vs. Input Frequency, 1 MSPS
20110251 20110252
ADC121S101/ADC101S101/ADC081S101
www.national.com13
Typical Performance Characteristics T
A
= +25˚C, V
DD
= 3V, f
SAMPLE
= 1 MSPS, f
SCLK
= 20 MHz, f
IN
= 100 kHz unless otherwise stated. (Continued)
ADC121S101 SINAD vs. Input Frequency, 600 kSPS ADC121S101 SINAD vs. Input Frequency, 1 MSPS
20110253 20110254
ADC121S101 SNR vs. f
SCLK
ADC121S101 SINAD vs. f
SCLK
20110256 20110257
ADC121S101/ADC101S101/ADC081S101
www.national.com 14
Typical Performance Characteristics T
A
= +25˚C, V
DD
= 3V, f
SAMPLE
= 1 MSPS, f
SCLK
= 20 MHz, f
IN
= 100 kHz unless otherwise stated. (Continued)
ADC101S101 DNL ADC101S101 INL
20110270 20110271
ADC101S101 Spectral Response @100 kHz Input ADC101S101 SNR vs. f
SCLK
20110272 20110273
ADC101S101 SINAD vs. f
SCLK
20110274
ADC121S101/ADC101S101/ADC081S101
www.national.com15
Typical Performance Characteristics T
A
= +25˚C, V
DD
= 3V, f
SAMPLE
= 1 MSPS, f
SCLK
= 20 MHz, f
IN
= 100 kHz unless otherwise stated. (Continued)
ADC081S101 DNL ADC081S101 INL
20110260 20110261
ADC081S101 Spectral Response @100 kHz Input ADC081S101 SNR vs. f
SCLK
20110262 20110263
ADC081S101 SINAD vs. f
SCLK
20110264
ADC121S101/ADC101S101/ADC081S101
www.national.com 16
Applications Information
1.0 ADC121S101/101S101/081S101 OPERATION
The ADC121S101/101S101/081S101 are successive-
approximation analog-to-digital converters designed around
a charge-redistribution digital-to-analog converter. Simplified
schematics of the ADC121S101/101S101/081S101 in both
track and hold operation are shown in Figures 4 and 5,
respectively. In Figure 4, the device is in track mode: switch
SW1 connects the sampling capacitor to the input, and SW2
balances the comparator inputs. The device is in this state
until CS is brought low, at which point the device moves to
hold mode.
Figure 5 shows the device in hold mode: switch SW1 con-
nects the sampling capacitor to ground, maintaining the
sampled voltage, and switch SW2 unbalances the compara-
tor. The control logic then instructs the charge-redistribution
DAC to add or subtract fixed amounts of charge from the
sampling capacitor until the comparator is balanced. When
the comparator is balanced, the digital word supplied to the
DAC is the digital representation of the analog input voltage.
The device moves from hold mode to track mode on the 13th
rising edge of SCLK.
2.0 USING THE ADC121S101/101S101/081S101
Serial interface timing diagrams for the ADC121S101/
101S101/081S101 are shown in Figures 1, 2, and 3. CS is
chip select, which initiates conversions on the ADC121S101/
101S101/081S101 and frames the serial data transfers.
SCLK (serial clock) controls both the conversion process
and the timing of serial data. SDATA is the serial data out pin,
where a conversion result is found as a serial data stream.
Basic operation of the ADC121S101/101S101/081S101 be-
gins with CS going low, which initiates a conversion process
and data transfer. Subsequent rising and falling edges of
SCLK will be labelled with reference to the falling edge of
CS; for example, "the third falling edge of SCLK" shall refer
to the third falling edge of SCLK after CS goes low.
At the fall of CS, the SDATA pin comes out of TRI-STATE,
and the converter moves from track mode to hold mode. The
input signal is sampled and held for conversion on the falling
edge of CS. The converter moves from hold mode to track
mode on the 13th rising edge of SCLK (see Figure 1, 2, or 3).
The SDATA pin will be placed back into TRI-STATE after the
16th falling edge of SCLK, or at the rising edge of CS,
whichever occurs first. After a conversion is completed, the
quiet time t
QUIET
must be satisfied before bringing CS low
again to begin another conversion.
Sixteen SCLK cycles are required to read a complete
sample from the ADC121S101/101S101/081S101. The
sample bits (including any leading or trailing zeroes) are
clocked out on falling edges of SCLK, and are intended to be
clocked in by a receiver on subsequent falling edges of
SCLK. The ADC121S101/101S101/081S101 will produce
three leading zero bits on SDATA, followed by twelve, ten, or
eight data bits, most significant first. After the data bits, the
ADC101S101 will clock out two trailing zeros, and the
ADC081S101 will clock out four trailing zeros. The
ADC121S101 will not clock out any trailing zeros; the least
significant data bit will be valid on the 16th falling edge of
SCLK.
20110209
FIGURE 4. ADC121S101/101S101/081S101 in Track Mode
20110210
FIGURE 5. ADC121S101/101S101/081S101 in Hold Mode
ADC121S101/ADC101S101/ADC081S101
www.national.com17
Applications Information (Continued)
If CS goes low before the rising edge of SCLK, an additional
(fourth) zero bit may be captured by the next falling edge of
SCLK.
3.0 ADC121S101/101S101/081S101 TRANSFER
FUNCTION
The output format of the ADC121S101/101S101/081S101 is
straight binary. Code transitions occur midway between suc-
cessive integer LSB values. The LSB widths for the
ADC121S101 is V
DD
/ 4096; for the ADC101S101 the LSB
width is V
DD
/ 1024; for the ADC081S101, the LSB width is
V
DD
/ 256. The ideal transfer characteristic for the
ADC121S101 and ADC101S101 is shown in Figure 6, while
the ideal transfer characteristic for the ADC081S101 is
shown in Figure 7.
20110211
FIGURE 6. ADC121S101/101S101 Ideal Transfer Characteristic
20110212
FIGURE 7. ADC081S101 Ideal Transfer Characteristic
ADC121S101/ADC101S101/ADC081S101
www.national.com 18
Applications Information (Continued)
4.0 SAMPLE CIRCUIT
A typical application of the ADC121S101/101S101/081S101
is shown in Figure 8. The combined analog and digital
supplies are provided in this example by the National
LP2950 low-dropout voltage regulator, available in a variety
of fixed and adjustable output voltages. The supply is by-
passed with a capacitor network located close to the device.
The three-wire interface is also shown connected to a micro-
processor or DSP.
5.0 ANALOG INPUTS
An equivalent circuit for the ADC121S101/101S101/
081S101 input channel is shown in Figure 9. The diodes D1
and D2 provide ESD protection for the analog inputs. At no
time should an analog input exceed V
DD
+ 300 mV or GND
- 300 mV, as these ESD diodes will begin conducting current
into the substrate and affect ADC operation.
The capacitor C1 in Figure 9 typically has a value of 4 pF,
and is mainly due to pin capacitance. The resistor R1 repre-
sents the on resistance of the multiplexer and track / hold
switch, and is typically 100 ohms. The capacitor C2 is the
ADC121S101/101S101/081S101 sampling capacitor, and is
typically 26 pF.
The sampling nature of the analog input causes input current
pulses that result in voltage spikes at the input. The
ADC121S101/101S101/081S101 will deliver best perfor-
mance when driven by a low-impedance source to eliminate
distortion caused by the charging of the sampling capaci-
tance. In applications where dynamic performance is critical,
the input might need to be driven with a low output-
impedance amplifier. In addition, when using the
ADC121S101/101S101/081S101 to sample AC signals, a
band-pass or low-pass filter will reduce harmonics and noise
and thus improve THD and SNR.
6.0 DIGITAL INPUTS AND OUTPUTS
The ADC121S101/101S101/081S101 digital inputs (SCLK
and CS) are not limited by the same absolute maximum
ratings as the analog inputs. The digital input pins are in-
stead limited to +6.5V with respect to GND, regardless of
V
DD
, the supply voltage. This allows the ADC121S101/
101S101/081S101 to be interfaced with a wide range of logic
levels, independent of the supply voltage.
Note that, even though the digital inputs are tolerant of up to
+6.5V above GND, the digital outputs are only capable of
driving V
DD
out. In addition, the digital input pins are not
prone to latch-up; SCLK and CS may be asserted before
V
DD
without any risk.
7.0 MODES OF OPERATION
The ADC121S101/101S101/081S101 has two possible
modes of operation: normal mode, and shutdown mode. The
ADC121S101/101S101/081S101 enters normal mode (and
a conversion process is begun) when CS is pulled low. The
device will enter shutdown mode if CS is pulled high before
the tenth falling edge of SCLK after CS is pulled low, or will
stay in normal mode if CS remains low. Once in shutdown
mode, the device will stay there until CS is brought low
again. By varying the ratio of time spent in the normal and
shutdown modes, a system may trade-off throughput for
power consumption.
8.0 NORMAL MODE
The best possible throughput is obtained by leaving the
ADC121S101/101S101/081S101 in normal mode at all
times, so there are no power-up delays. To keep the device
in normal mode continuously, CS must be kept low until after
the 10th falling edge of SCLK after the start of a conversion
(remember that a conversion is initiated by bringing CS low).
If CS is brought high after the 10th falling edge, but before
the 16th falling edge, the device will remain in normal mode,
but the current conversion will be aborted, and SDATA will
return to TRI-STATE (truncating the output word).
Sixteen SCLK cycles are required to read all of a conversion
word from the device. After sixteen SCLK cycles have
elapsed, CS may be idled either high or low until the next
conversion. If CS is idled low, it must be brought high again
before the start of the next conversion, which begins when
CS is again brought low.
After sixteen SCLK cycles, SDATA returns to TRI-STATE.
Another conversion may be started, after t
QUIET
has
elapsed, by bringing CS low again.
20110213
FIGURE 8. Sample Circuit
20110214
FIGURE 9. Equivalent Input Circuit
ADC121S101/ADC101S101/ADC081S101
www.national.com19
Applications Information (Continued)
9.0 SHUTDOWN MODE
Shutdown mode is appropriate for applications that either do
not sample continuously, or are willing to trade throughput
for power consumption. When the ADC121S101/101S101/
081S101 is in shutdown mode, all of the analog circuitry is
turned off.
To enter shutdown mode, a conversion must be interrupted
by bringing CS back high anytime between the second and
tenth falling edges of SCLK, as shown in Figure 10. Once CS
has been brought high in this manner, the device will enter
shutdown mode; the current conversion will be aborted and
SDATA will enter TRI-STATE. If CS is brought high before the
second falling edge of SCLK, the device will not change
mode; this is to avoid accidentally changing mode as a result
of noise on the CS line.
10.0 EXITING SHUTDOWN MODE
To exit shutdown mode, bring CS back low. Upon bringing
CS low, the ADC121S101/101S101/081S101 will begin pow-
ering up. Power up typically takes 1 µs. This microsecond of
power-up delay results in the first conversion result being
unusable. The second conversion performed after power-up,
however, is valid, as shown in Figure 11.
If CS is brought back high before the 10th falling edge of
SCLK, the device will return to shutdown mode. This is done
to avoid accidentally entering normal mode as a result of
noise on the CS line. To exit shutdown mode and remain in
normal mode, CS must be kept low until after the 10th falling
edge of SCLK. The ADC121S101/101S101/081S101 will be
fully powered-up after 16 SCLK cycles.
11.0 POWER-UP TIMING
The ADC121S101/101S101/081S101 typically requires 1 µs
to power up, either after first applying V
DD
, or after returning
to normal mode from shutdown mode. This corresponds to
one "dummy" conversion for any SCLK frequency within the
specifications in this document. After this first dummy con-
version, the ADC121S101/101S101/081S101 will perform
conversions properly. Note that the t
QUIET
time must still be
included between the first dummy conversion and the sec-
ond valid conversion.
12.0 STARTUP MODE
When the V
DD
supply is first applied, the ADC121S101/
101S101/081S101 may power up in either of the two modes:
normal or shutdown. As such, one dummy conversion
should be performed after start-up, exactly as described in
Section 11.0. The part may then be placed into either normal
mode or the shutdown mode, as described in Sections 8.0
and 9.0.
13.0 POWER MANAGEMENT
When the ADC121S101/101S101/081S101 is operated con-
tinuously in normal mode, throughput up to 1 MSPS can be
achieved. The user may trade throughput for power con-
sumption by simply performing fewer conversions per unit
time, and putting the ADC121S101/101S101/081S101 into
shutdown mode between conversions. This method is not
advantageous beyond 350 kSPS throughput.
A plot of maximum power consumption versus throughput is
shown in Figure 12 below. To calculate the power consump-
tion for a given throughput, remember that each time the part
exits shutdown mode and enters normal mode, one dummy
conversion is required. Generally, the user will put the part
into normal mode, execute one dummy conversion followed
by one valid conversion, and then put the part back into
shutdown mode. When this is done, the fraction of time
20110216
FIGURE 10. Entering Shutdown Mode
20110217
FIGURE 11. Entering Normal Mode
ADC121S101/ADC101S101/ADC081S101
www.national.com 20
Applications Information (Continued)
spent in normal mode may be calculated by multiplying the
throughput (in samples per second) by 2 µs, the time taken
to perform one dummy and one valid conversion. The power
consumption can then be found by multiplying the fraction of
time spent in normal mode by the normal mode power
consumption figure. The power dissipated while the part is in
shutdown mode is negligible.
For example, to calculate the power consumption at 300
kSPS with V
DD
= 5V, begin by calculating the fraction of time
spent in normal mode: 300,000 samples/second·2µs=0.6,
or 60%. The power consumption at 300 kSPS is then 60% of
17.5 mW (the maximum power consumption at V
DD
= 5V) or
10.5 mW.
20110255
FIGURE 12. Maximum Power Consumption vs. Throughput
ADC121S101/ADC101S101/ADC081S101
www.national.com21
Physical Dimensions inches (millimeters) unless otherwise noted
6-Lead SOT-23
Order Number ADC121S101CIMF, ADC121S101CIMFX, ADC101S101CIMF, ADC101S101CIMFX, ADC081S101CIMF or
ADC081S101CIMFX
NS Package Number MF06A
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ADC121S101/ADC101S101/ADC081S101 1MSPS, 12-/10-/8-Bit A/D Converters in SOT-23
National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications.