ADC12020
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SNAS186B – APRIL 2003 – REVISED MARCH 2013
ADC12020 12-Bit, 20 MSPS, 185 mW A/D Converter with Internal Sample-and-Hold
Check for Samples: ADC12020
FEATURES
DESCRIPTION
•
•
•
The ADC12020 is a monolithic CMOS analog-todigital converter capable of converting analog input
signals into 12-bit digital words at 20 Megasamples
per second (MSPS), minimum. This converter uses a
differential, pipeline architecture with digital error
correction and an on-chip sample-and-hold circuit to
minimize die size and power consumption while
providing excellent dynamic performance. Operating
on a single 5V power supply, this device consumes
just 185 mW at 20 MSPS, including the reference
current. The Power Down feature reduces power
consumption to 40 mW.
1
23
•
•
•
Internal sample-and-hold
Outputs 2.35V to 5V compatible
Pin compatible with ADC12010, ADC12040,
ADC12L063 and ADC12L066
TTL/CMOS compatible input/outputs
Power down mode
On-chip reference buffer
APPLICATIONS
•
•
•
•
•
•
•
Image Processing Front End
Instrumentation
PC-Based Data Acquisition
Fax Machines
Waveform Digitizers
Sonar/Radar
DSP Front Ends
KEY SPECIFICATIONS
•
•
•
•
•
•
Resolution 12 Bits
Conversion Rate 20 MSPS (min)
DNL ±0.35 LSB (typ)
ENOB (fIN = 10.1 MHz) 11.3 bits (typ)
Supply Voltage +5 / ±5 V / %
Power Consumption, 20 MHz 185 mW (typ)
The differential inputs provide a full scale input swing
equal to 2VREF with the possibility of a single-ended
input. Full use of the differential input is
recommended for optimum performance. For ease of
use, the buffered, high impedance, single-ended
reference input is converted on-chip to a differential
reference for use by the processing circuitry. Output
data format is 12-bit offset binary.
This device is available in the 32-lead LQFP package
and will operate over the industrial temperature range
of −40°C to +85°C.
1
2
3
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
TRI-STATE is a trademark of Texas Instruments.
All other trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2003–2013, Texas Instruments Incorporated
ADC12020
SNAS186B – APRIL 2003 – REVISED MARCH 2013
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These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
Connection Diagram
Figure 1. 32-Lead LQFP
See NEY0032A Package
Block Diagram
2
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Pin Descriptions and Equivalent Circuits
Pin No.
Symbol
Equivalent Circuit
Description
ANALOG I/O
2
3
VIN+
Non-Inverting analog signal Input. With a 2.0V reference voltage, the
differential input signal level is 2.0 VP-P centered on VCM.
VIN−
Inverting analog signal Input. With a 2.0V reference voltage the groundreferenced input signal level is 2.0 VP-P centered on VCM. This pin may be
connected to VCM for single-ended operation, but a differential input signal
is required for best performance.
VA
1
Reference input. This pin should be bypassed to AGND with a 0.1 µF
monolithic capacitor. VREF is 2.0V nominal and should be between 1.0V to
2.2V.
VREF
AGND
31
VRP
32
VRM
These pins are high impedance reference bypass pins. Connect a 0.1 µF
capacitor from each of these pins to AGND. DO NOT LOAD these pins.
30
VRN
DIGITAL I/O
10
CLK
Digital clock input. The range of frequencies for this input is 100 kHz to 30
MHz (typical) with specified performance at 20 MHz. The input is sampled
on the rising edge of this input.
11
OE
OE is the output enable pin that, when low, enables the TRI-STATE™ data
output pins. When this pin is high, the outputs are in a high impedance
state.
8
PD
PD is the Power Down input pin. When high, this input puts the converter
into the power down mode. When this pin is low, the converter is in the
active mode.
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Pin No.
Symbol
14–19,
22–27
D0–D11
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Equivalent Circuit
Description
Digital data output pins that make up the 12-bit conversion results. D0 is
the LSB, while D11 is the MSB of the offset binary output word. Output
levels are TTL/CMOS compatible.
ANALOG POWER
5, 6, 29
4, 7, 28
VA
AGND
Positive analog supply pins. These pins should be connected to a quiet
+5V voltage source and bypassed to AGND with 0.1 µF monolithic
capacitors located within 1 cm of these power pins, and with a 10 µF
capacitor.
The ground return for the analog supply.
DIGITAL POWER
4
13
VD
9, 12
DGND
21
VDR
20
DR GND
Positive digital supply pin. This pin should be connected to the same quiet
+5V source as is VA and bypassed to DGND with a 0.1 µF monolithic
capacitor in parallel with a 10 µF capacitor, both located within 1 cm of the
power pin.
The ground return for the digital supply.
Positive digital supply pin for the ADC12020's output drivers. This pin
should be connected to a voltage source of +2.35V to +5V and be
bypassed to DR GND with a 0.1 µF monolithic capacitor. If the supply for
this pin is different from the supply used for VA and VD, it should also be
bypassed with a 10 µF tantalum capacitor. VDR should never exceed the
voltage on VD. All bypass capacitors should be located within 1 cm of the
supply pin.
The ground return for the digital supply for the ADC12020's output drivers.
This pin should be connected to the system digital ground, but not be
connected in close proximity to the ADC12020's DGND or AGND pins. See
LAYOUT AND GROUNDING for more details.
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ABSOLUTE MAXIMUM RATINGS
(1) (2)
VA, VD
6.5V
≤VD+0.3V
VDR
≤ 100 mV
|VA–VD|
−0.3V to (VA or VD + 0.3V)
Voltage on Any Input or Output Pin
Input Current at Any Pin
(3)
±25 mA
(3)
Package Input Current
±50 mA
Package Dissipation at TA = 25°C
See
(4)
ESD Susceptibility
Human Body Model
Machine Model
(5)
2500V
(5)
Soldering Temperature,
250V
Infrared, 10 sec.
(6)
235°C
−65°C to +150°C
Storage Temperature
(1)
(2)
(3)
(4)
(5)
(6)
All voltages are measured with respect to GND = AGND = DGND = 0V, unless otherwise specified.
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is functional, but do not ensure specific performance limits. For specifications and test conditions, see the Electrical
Characteristics. The specified specifications apply only for the test conditions listed. Some performance characteristics may degrade
when the device is not operated under the listed test conditions.
When the input voltage at any pin exceeds the power supplies (that is, VIN < AGND, or VIN > VA), the current at that pin should be
limited to 25 mA. The 50 mA maximum package input current rating limits the number of pins that can safely exceed the power supplies
with an input current of 25 mA to two.
The absolute maximum junction temperature (TJmax) for this device is 150°C. The maximum allowable power dissipation is dictated by
TJmax, the junction-to-ambient thermal resistance (θJA), and the ambient temperature, (TA), and can be calculated using the formula
PDMAX = (TJmax - TA )/θJA. The values for maximum power dissipation listed above will be reached only when the device is operated in
a severe fault condition (e.g. when input or output pins are driven beyond the power supply voltages, or the power supply polarity is
reversed). Obviously, such conditions should always be avoided.
Human body model is 100 pF capacitor discharged through a 1.5 kΩ resistor. Machine model is 220 pF discharged through 0Ω.
The 235°C reflow temperature refers to infrared reflow. For Vapor Phase Reflow (VPR), the following Conditions apply: Maintain the
temperature at the top of the package body above 183°C for a minimum 60 seconds. The temperature measured on the package body
must not exceed 220°C. Only one excursion above 183°C is allowed per reflow cycle.
OPERATING RATINGS
(1) (2)
Operating Temperature
−40°C ≤ TA ≤ +85°C
Supply Voltage (VA, VD)
+4.75V to +5.25V
Output Driver Supply (VDR)
+2.35V to VD
VREF Input
1.0V to 2.4V
−0.05V to (VD + 0.05V)
CLK, PD, OE
−0V to (VA − 0.5V)
VIN Input
VCM
1.0V to 4.0V
≤100mV
|AGND–DGND|
(1)
(2)
Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is functional, but do not ensure specific performance limits. For specifications and test conditions, see the Electrical
Characteristics. The specifications apply only for the test conditions listed. Some performance characteristics may degrade when the
device is not operated under the listed test conditions.
All voltages are measured with respect to GND = AGND = DGND = 0V, unless otherwise specified.
PACKAGE THERMAL RESISTANCE
Package
θJA
32-Lead LQFP
79°C / W
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CONVERTER ELECTRICAL CHARACTERISTICS
Unless otherwise specified, the following specifications apply for AGND = DGND = DR GND = 0V, VA = VD = +5V, VDR =
+3.0V, PD = 0V, VREF = +2.0V, fCLK = 20 MHz, tr = tf = 3 ns, CL = 25 pF/pin. Boldface limits apply for TJ = TMIN to TMAX: all
other limits TA = TJ = 25°C (1) (2) (3)
Symbol
Parameter
Conditions
Typical
(4)
Limits
(4)
Units
(Limits)
STATIC CONVERTER CHARACTERISTICS
Resolution with No Missing Codes
INL
Integral Non Linearity
(5)
±0.55
12
Bits (min)
+1.7
LSB (max)
-1.4
LSB (min)
+0.9
LSB (max)
DNL
Differential Non Linearity
±0.35
-1.0
LSB (min)
GE
Gain Error
±0.05
2.9
%FS (max)
Offset Error (VIN+ = VIN−)
%FS (max)
−0.04
±1.75
Under Range Output Code
0
0
Over Range Output Code
4095
4095
DYNAMIC CONVERTER CHARACTERISTICS
FPBW
SNR
Full Power Bandwidth
Signal-to-Noise Ratio
SINAD
ENOB
THD
Signal-to-Noise and Distortion
Effective Number of Bits
Total Harmonic Distortion
0 dBFS Input, Output at −3 dB
100
MHz
fIN = 1 MHz, VIN = −0.5 dBFS
70
dB
fIN = 4.4 MHz, VIN = −0.5 dBFS
70
fIN = 10.1 MHz, VIN = −0.5 dBFS
70
fIN = 1 MHz, VIN = −0.5 dBFS
70
fIN = 4.4 MHz, VIN = −0.5 dBFS
70
fIN = 10.1MHz, VIN = −0.5 dBFS
69
Spurious Free Dynamic Range
Intermodulation Distortion
dB
dB
67
dB (min)
11.3
dB
fIN = 4.4 MHz, VIN = −0.5 dBFS
11.3
dB
fIN = 10.1 MHz, VIN = −0.5 dBFS
11.3
fIN = 1 MHz, VIN = −0.5 dBFS
−83
fIN = 4.4 MHz, VIN = −0.5 dBFS
−83
−83
+25°C
+85°C
fIN = 1 MHz, VIN = −0.5 dBFS
86
fIN = 4.4 MHz, VIN = −0.5 dBFS
86
fIN = 10.1 MHz,
VIN = −0.5 dBFS
IMD
dB (min)
fIN = 1 MHz, VIN = −0.5 dBFS
fIN = 10.1 MHz,
VIN = −0.5 dBFS
SFDR
dB
67
+25°C
86
+85°C
fIN = 4.7 MHz and 5.3 MHz, each = −7 dBFS
10.8
dB (min)
dB
dB
-74
dB (min)
-71
dB (min)
dB
dB
71
dB (min)
68
dB (min)
−73
dBFS
REFERENCE AND ANALOG INPUT CHARACTERISTICS
VCM
CIN
VREF
Common Mode Input Voltage
VIN Input Capacitance (each pin to GND)
Reference Voltage
VIN = 2.5 Vdc + 0.7 Vrms
VA/2
V
(CLK LOW)
8
pF
(CLK HIGH)
7
(6)
2.00
Reference Input Resistance
(1)
(2)
(3)
(4)
(5)
(6)
6
100
pF
1.0
2.4
V (min)
V (max)
MΩ(min)
The inputs are protected as shown below. Input voltage magnitudes above VA or below GND will not damage this device, provided
current is limited per ABSOLUTE MAXIMUM RATINGS (3). However, errors in the A/D conversion can occur if the input goes above VA
or below GND by more than 100 mV. As an example, if V is 4.75V, the full-scale input voltage must be ≤4.85V to ensure accurate
conversions.
To ensure accuracy, Ait is required that |VA–VD| ≤ 100 mV and separate bypass capacitors are used at each power supply pin.
With the test condition for VREF = +2.0V (4VP-P differential input), the 12-bit LSB is 977 µV.
Typical figures are at TA = TJ = 25°C, and represent most likely parametric norms. Test limits are specified to TI's AOQL (Average
Outgoing Quality Level).
Integral Non Linearity is defined as the deviation of the analog value, expressed in LSBs, from the straight line that passes through
positive and negative full-scale.
Optimum performance will be obtained by keeping the reference input in the 1.8V to 2.2V range. The LM4051CIM3-ADJ (SOT-23
package) is recommended for this application.
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DC and LOGIC ELECTRICAL CHARACTERISTICS
Unless otherwise specified, the following specifications apply for AGND = DGND = DR GND = 0V, VA = VD = +5V, VDR =
+3.0V, PD + 0V, VREF = +2.0V, fCLK = 20 MHz, tr = tf = 3 ns, CL = 25 pF/pin. Boldface limits apply for TJ = TMIN to TMAX: all
other limits TA = TJ = 25°C (1) (2) (3)
Symbol
Parameter
Conditions
Typical (4)
Limits (4)
Units
(Limits)
CLK, PD, OE DIGITAL INPUT CHARACTERISTICS
VIN(1)
Logical “1” Input Voltage
VD = 5.25V
2.0
V (min)
VIN(0)
Logical “0” Input Voltage
VD = 4.75V
1.0
V (max)
IIN(1)
Logical “1” Input Current
VIN = 5.0V
10
µA
IIN(0)
Logical “0” Input Current
VIN = 0V
−10
µA
CIN
Digital Input Capacitance
5
pF
D0–D11 DIGITAL OUTPUT CHARACTERISTICS
VDR = 2.5V
2.3
V (min)
VDR = 3V
2.7
V (min)
0.4
V (max)
VOUT(1)
Logical “1” Output Voltage
IOUT = −0.5 mA
VOUT(0)
Logical “0” Output Voltage
IOUT = 1.6 mA, VDR = 3V
IOZ
TRI-STATE™ Output Current
VOUT = 0V
−100
nA
+ISC
Output Short Circuit Source Current
VOUT = 0V
−20
mA (min)
−ISC
Output Short Circuit Sink Current
VOUT = VDR
20
mA (min)
VOUT = 2.5V or 5V
100
nA
POWER SUPPLY CHARACTERISTICS
IA
Analog Supply Current
PD Pin = DGND, VREF = 2.0V
PD Pin = VDR
32.3
8
41
mA (max)
mA
ID
Digital Supply Current
PD Pin = DGND
PD Pin = VDR, fCLK = 0
3.3
3.5
4.5
mA (max)
mA
Digital Output Supply Current
PD Pin = DGND, CL = 0 pF
PD Pin = VDR, fCLK = 0
(5)
IDR
3
0
PD Pin = DGND, CL = 0 pF
PD Pin = VDR, fCLK = 0
(6)
Total Power Consumption
178
40
PSRR1+
Power Supply Rejection Ratio
PSRR1−
Power Supply Rejection Ratio
PSRR2
Power Supply Rejection Ratio
(1)
(2)
(3)
(4)
(5)
(6)
Rejection of Positive Full-Scale Error with
VA = 4.75V to 5.25V
Rejection of Power Supply Noise with
10 MHz, 250 mVP-P riding on VA
mA (max)
mA
227
mW
mW
69
dBFS
51
dBFS
48
dBFS
The inputs are protected as shown below. Input voltage magnitudes above VA or below GND will not damage this device, provided
current is limited per ABSOLUTE MAXIMUM RATINGS (3). However, errors in the A/D conversion can occur if the input goes above VA
or below GND by more than 100 mV. As an example, if VA is 4.75V, the full-scale input voltage must be ≤4.85V to ensure accurate
conversions.
To ensure accuracy, it is required that |VA–VD| ≤ 100 mV and separate bypass capacitors are used at each power supply pin.
With the test condition for VREF = +2.0V (4VP-P differential input), the 12-bit LSB is 977 µV.
Typical figures are at TA = TJ = 25°C, and represent most likely parametric norms. Test limits are specified to TI's AOQL (Average
Outgoing Quality Level).
IDR is the current consumed by the switching of the output drivers and is primarily determined by load capacitance on the output pins,
the supply voltage, VDR, and the rate at which the outputs are switching (which is signal dependent). IDR=VDR(C0 x f0 + C1 x f1 +....C11 x
f11) where VDR is the output driver power supply voltage, Cn is total capacitance on the output pin, and fn is the average frequency at
which that pin is toggling.
Excludes IDR. See note 14.
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AC ELECTRICAL CHARACTERISTICS
Unless otherwise specified, the following specifications apply for AGND = DGND = DR GND = 0V, VA = VD = +5V, VDR =
+3.0V, PD = 0V, VREF = +2.0V, fCLK = 20 MHz, tr = tf = 3 ns, CL = 25 pF/pin. Boldface limits apply for TJ = TMIN to TMAX: all
other limits TA = TJ = 25°C (1) (2) (3) (4)
Symbol
Parameter
Conditions
Typical
fCLK1
Maximum Clock Frequency
20
fCLK
Minimum Clock Frequency
100
tCH
(5)
Limits
(5)
Units
(Limits)
30
MHz (min)
Clock High Time
20
ns (min)
tCL
Clock Low Time
20
ns (min)
tCONV
Conversion Latency
6
Clock Cycles
tOD
Data Output Delay after Rising CLK Edge
tAD
Aperture Delay
1.2
ns
tAJ
Aperture Jitter
2
ps rms
tDIS
Data outputs into TRI-STATE™ Mode
4
ns
tEN
Data Outputs Active after TRI-STATE™
4
ns
tPD
Power Down Mode Exit Cycle
500
ns
2
kHz
VDR = 2.5V
11
16.8
ns (max)
VDR = 3.0V
11
16.8
ns (max)
0.1µF capacitors on pins 30, 31, 32
(1)
7The inputs are protected as shown below. Input voltage magnitudes above VA or below GND will not damage this device, provided
current is limited per ABSOLUTE MAXIMUM RATINGS (3). However, errors in the A/D conversion can occur if the input goes above VA
or below GND by more than 100 mV. As an example, if VA is 4.75V, the full-scale input voltage must be ≤4.85V to ensure accurate
conversions.
(2)
(3)
(4)
(5)
To ensure accuracy, it is required that |VA–VD| ≤ 100 mV and separate bypass capacitors are used at each power supply pin.
With the test condition for VREF = +2.0V (4VP-P differential input), the 12-bit LSB is 977 µV.
Timing specifications are tested at TTL logic levels, VIL = 0.4V for a falling edge and VIH = 2.4V for a rising edge.
Typical figures are at TA = TJ = 25°C, and represent most likely parametric norms. Test limits are specific to TI's AOQL (Average
Outgoing Quality Level).
8
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Specification Definitions
APERTURE DELAY is the time after the rising edge of the clock 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.
CLOCK DUTY CYCLE is the ratio of the time during one cycle that a repetitive digital waveform is high to the
total time of one period. The specification here refers to the ADC clock input signal.
COMMON MODE VOLTAGE (VCM) is the d.c. potential present at both signal inputs to the ADC.
CONVERSION LATENCY See PIPELINE DELAY.
DIFFERENTIAL NON-LINEARITY (DNL) is the measure of the maximum deviation from the ideal step size of 1
LSB.
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 = Pos. Full Scale Error − Neg. Full Scale Error
(1)
GAIN ERROR is the deviation from the ideal slope of the transfer function. It is the difference between the input
that cause a transition from all zeros to the first code.
INTEGRAL NON LINEARITY (INL) is a measure of the deviation of each individual code from a line drawn from
negative full scale (½ LSB below the first code transition) through positive full scale (½ 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 intermodulation products to the total power in the original frequencies. IMD is usually expressed in dBFS.
MISSING CODES are those output codes that will never appear at the ADC outputs. The ADC12020 is ensured
not to have any missing codes.
NEGATIVE FULL SCALE ERROR is the difference between the actual first code transition and its ideal value of
½ LSB above negative full scale.
OFFSET ERROR is the difference between the two input voltages (VIN + –VIN−) required to cause a transition
from code 2047 to 2048.
OUTPUT DELAY is the time delay after the rising edge of the clock before the data update is presented at the
output pins.
PIPELINE DELAY (LATENCY) is the number of clock cycles between initiation of conversion and when that data
is presented to the output driver stage. Data for any given sample is available at the output pins the Pipeline
Delay plus the Output Delay after the sample is taken. New data is available at every clock cycle, but the data
lags the conversion by the pipeline delay.
POSITIVE FULL SCALE ERROR is the difference between the actual last code transition and its ideal value of
1½ LSB below positive full scale.
POWER SUPPLY REJECTION RATIO (PSRR) is a measure of how well the ADC rejects a change in the power
supply voltage. For the ADC12020, PSRR1 is the ratio of the change in Full-Scale Error that results from a
change in the dc power supply voltage, expressed in dB. PSRR2 is a measure of how well an a.c. signal riding
upon the power supply is rejected at the output.
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.
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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 components below half the clock frequency, including
harmonics but excluding dc.
SPURIOUS FREE DYNAMIC RANGE (SFDR) is the difference, expressed in dB, between the desired signal
amplitude to the amplitude of the peak spurious spectral component, where a spurious spectral component is
any signal present in the output spectrum that is not present at the input and may or may not be a harmonic.
TOTAL HARMONIC DISTORTION (THD) is the ratio, expressed in dBc, of the rms total of the first nine
harmonic levels at the output to the level of the fundamental at the output. THD is calculated as
(2)
where f1 is the RMS power of the fundamental (output) frequency and f2 through f10 are the RMS power in the
first 9 harmonic frequencies.
Timing Diagram
Figure 2. Output Timing
Transfer Characteristic
Figure 3. Transfer Characteristic
10
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ADC12020 TYPICAL PERFORMANCE CHARACTERISTICS
VA = VD = 5V, VDR = 3.0V, fCLK = 20 MHz, fIN = 10.1 MHz, VREF = 2.0V unless otherwise stated
DNL
DNL vs. Temperature
Figure 4.
Figure 5.
DNL vs. Clock Duty Cycle
DNL vs. Sample Rate
Figure 6.
Figure 7.
INL
INL vs. Temperature
Figure 8.
Figure 9.
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ADC12020 TYPICAL PERFORMANCE CHARACTERISTICS (continued)
VA = VD = 5V, VDR = 3.0V, fCLK = 20 MHz, fIN = 10.1 MHz, VREF = 2.0V unless otherwise stated
12
INL vs. Clock Duty Cycle
INL vs. Sample Rate
Figure 10.
Figure 11.
SN vs. Temperature
SNR vs. Clock Duty Cycle
Figure 12.
Figure 13.
SNR vs. Sample Rate
SNR vs. FIN
Figure 14.
Figure 15.
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ADC12020 TYPICAL PERFORMANCE CHARACTERISTICS (continued)
VA = VD = 5V, VDR = 3.0V, fCLK = 20 MHz, fIN = 10.1 MHz, VREF = 2.0V unless otherwise stated
SNR vs. VREF
THD vs. Temperature
Figure 16.
Figure 17.
THD vs. Clock Duty Cycle
THD vs. Sample Rate
Figure 18.
Figure 19.
THD vs. FIN
THD vs. VREF
Figure 20.
Figure 21.
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ADC12020 TYPICAL PERFORMANCE CHARACTERISTICS (continued)
VA = VD = 5V, VDR = 3.0V, fCLK = 20 MHz, fIN = 10.1 MHz, VREF = 2.0V unless otherwise stated
14
SINAD vs. Temperature
SINAD vs. Clock Duty Cycle
Figure 22.
Figure 23.
SINAD vs. Sample Rate
SINAD vs. FIN
Figure 24.
Figure 25.
SINAD vs. VREF
SFDR vs. Temperature
Figure 26.
Figure 27.
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ADC12020 TYPICAL PERFORMANCE CHARACTERISTICS (continued)
VA = VD = 5V, VDR = 3.0V, fCLK = 20 MHz, fIN = 10.1 MHz, VREF = 2.0V unless otherwise stated
SFDR vs. Clock Duty Cycle
SFDR vs. Sample Rate
Figure 28.
Figure 29.
SFDR vs. FIN
SFDR vs. VREF
Figure 30.
Figure 31.
TOD vs. VDR
Spectral Response, 1.1 MHz Input
Figure 32.
Figure 33.
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ADC12020 TYPICAL PERFORMANCE CHARACTERISTICS (continued)
VA = VD = 5V, VDR = 3.0V, fCLK = 20 MHz, fIN = 10.1 MHz, VREF = 2.0V unless otherwise stated
Spectral Response, 44 MHz Input
Spectral Response, 10.1 MHz Input
Figure 34.
Figure 35.
Spectral Response
IMD @ F1 = 9.5MHz, F2 = 10.5MHz
Figure 36.
Figure 37.
Functional Description
Operating on a single +5V supply, the ADC12020 uses a pipeline architecture and has error correction circuitry
to help ensure maximum performance. The differential analog input signal is digitized to 12 bits.
The reference input is buffered to ease the task of driving that pin. The output word rate is the same as the clock
frequency. The analog input voltage is acquired at the rising edge of the clock and the digital data for a given
sample is delayed by the pipeline for 6 clock cycles.
A logic high on the power down (PD) pin reduces the converter power consumption to 40 mW.
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APPLICATIONS INFORMATION
OPERATING CONDITIONS
We recommend that the following conditions be observed for operation of the ADC12020:
• 4.75V ≤ VA ≤ 5.25V
• VD = VA
• 2.35V ≤ VDR ≤ VD
• 100 kHz ≤ fCLK ≤ 30 MHz
• 1.0V ≤ VREF ≤ 2.4V
• 1.0V ≤ VCM ≤ 4.0V
Analog Inputs
The ADC12020 has two analog signal inputs, VIN+ and VIN−. These two pins form a differential input pair. There
is one reference input pin, VREF.
Reference Pins
The ADC12020 is designed to operate with a 2.0V reference, but performs well with reference voltages in the
range of 1.0V to 2.4V. Lower reference voltages will decrease the signal-to-noise ratio (SNR). Increasing the
reference voltage (and the input signal swing) beyond 2.4V will degrade THD for a full-scale input.
It is very important that all grounds associated with the reference voltage and the input signal make connection to
the ground plane at a single point to minimize the effects of noise currents in the ground path.
The three Reference Bypass Pins (VRP, VRM and VRN) are made available for bypass purposes. These pins
should each be bypassed to ground with a 0.1 µF capacitor. Smaller capacitor values will allow faster recovery
from the power down mode, but may result in degraded noise performance. DO NOT LOAD these pins.
Signal Inputs
The signal inputs are VIN+ and VIN−. The input signal, VIN, is defined as
VIN = (VIN+) – (VIN−)
(3)
Figure 38 shows the expected input signal range.
Note that the common mode input voltage range is 1V to 3V with a nominal value of VA/2. The input signals
should remain between ground and 4V.
The Peaks of the individual input signals (VIN+ and VIN−) should each never exceed the voltage described as
VIN+, VIN− = VREF + VCM
(4)
to maintain THD and SINAD performance.
Figure 38. Expected Input Signal Range
The ADC12020 performs best with a differential input with each input centered around VCM. The peak-to-peak
voltage swing at both VIN+ and VIN− each should not exceed the value of the reference voltage or the output data
will be clipped. The two input signals should be exactly 180° out of phase from each other and of the same
amplitude. For single frequency inputs, angular errors result in a reduction of the effective full scale input. For a
complex waveform, however, angular errors will result in distortion.
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For angular deviations of up to 10 degrees from these two signals being 180 out of phase, the full scale error in
LSB can be described as approximately
EFS = 4096 ( 1 - sin (90° + dev))
(5)
Where dev is the angular difference, in degrees, between the two signals having a 180° relative phase
relationship to each other (see Figure 39). Drive the analog inputs with a source impedance less than 100Ω.
Figure 39. Angular Errors Between the Two Input Signals Will Reduce the Output Level
For differential operation, each analog input signal should have a peak-to-peak voltage equal to the input
reference voltage, VREF, and be centered around a common mode voltage, VCM.
Table 1. Input to Output Relationship—Differential Input
VIN
VIN−
Output
VCM − VREF/2
VCM + VREF/2
0000 0000 0000
VCM − VREF/4
VCM + VREF/4
0100 0000 0000
+
VCM
VCM
1000 0000 0000
VCM + VREF/4
VCM − VREF/4
1100 0000 0000
VCM + VREF/2
VCM − VREF/2
1111 1111 1111
Table 2. Input to Output Relationship—Single-Ended Input
VIN
VIN−
Output
VCM − VREF
VCM
0000 0000 0000
VCM − VREF/2
VCM
0100 0000 0000
VCM
VCM
1000 0000 0000
VCM + VREF/2
VCM
1100 0000 0000
VCM + VREF
VCM
1111 1111 1111
+
Single-Ended Operation
Single-ended performance is lower than with differential input signals. For this reason, single-ended operation is
not recommended. However, if single ended-operation is required, and the resulting performance degradation is
acceptable, one of the analog inputs should be connected to the d.c. common mode voltage of the driven input.
The peak-to-peak differential input signal should be twice the reference voltage to maximize SNR and SINAD
performance (Figure 38b). For example, set VREF to 1.0V, bias VIN− to 1.0V and drive VIN+ with a signal range of
0V to 2.0V.
Because very large input signal swings can degrade distortion performance, better performance with a singleended input can be obtained by reducing the reference voltage when maintaining a full-range output. Table 1 and
Table 2 indicate the input to output relationship of the ADC12020.
Driving the Analog Inputs
The VIN+ and the VIN− inputs of the ADC12020 consist of an analog switch followed by a switched-capacitor
amplifier. The capacitance seen at the analog input pins changes with the clock level, appearing as 8 pF when
the clock is low, and 7 pF when the clock is high. Although this difference is small, a dynamic capacitance is
more difficult to drive than is a fixed capacitance, so choose the driving amplifier carefully. The LMH6550, the
LMH6702 and the LM6628 are good amplifiers for driving the ADC12020.
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The internal switching action at the analog inputs causes energy to be output from the input pins. As the driving
source tries to compensate for this, it adds noise to the signal. To prevent this, use an RC at each of the inputs,
as shown in Figure 41 and Figure 42. These components should be placed close to the ADC because the input
pins of the ADC is the most sensitive part of the system and this is the last opportunity to filter the input. For
undersampling applications, the capacitors should be eliminated.
The LMH6550 and the LMH6552 are excellent devices for driving the ADC12020, especially when single-ended
to differential conversion with d.c. coupling is necessary. An example of the use of the LMH6550 to drive the
analog input of the ADC12020 is shown in Figure 41.
For high frequency, narrow band applications, a transformer is generally the recommended way to drive the
analog inputs, as shown in Figure 42.
Input Common Mode Voltage
The input common mode voltage, VCM, should be in the range of 0.5V to 4.0V and be of a value such that the
peak excursions of the analog signal does not go more negative than ground or more positive than 1.2 Volts
below the VA supply voltage. The nominal VCM should generally be equal to VREF/2, but VRM can be used as a
VCM source as long as VCM need not supply more than 10 µA of current. Figure 41 shows the use of the VRM
output to drive the VCM input of the LMH6550. The common mode output voltage of the LMH6550 is equal to the
VCM input input voltage.
DIGITAL INPUTS
The digital TTL/CMOS compatible inputs consist of CLK, OE and PD.
CLK
The CLK signal controls the timing of the sampling process. Drive the clock input with a stable, low jitter clock
signal in the range of 100 kHz to 30 MHz with rise and fall times of less than 3ns. The trace carrying the clock
signal should be as short as possible and should not cross any other signal line, analog or digital, not even at
90°.
If the CLK is interrupted, or its frequency too low, the charge on internal capacitors can dissipate to the point
where the accuracy of the output data will degrade. This is what limits the lowest sample rate to 100 ksps.
The duty cycle of the clock signal can affect the performance of the A/D Converter. Because achieving a precise
duty cycle is difficult, the ADC12020 is designed to maintain performance over a range of duty cycles. While it is
specified and performance is ensured with a 50% clock duty cycle, performance is typically maintained over a
clock duty cycle range of 40% to 60%.
The clock line should be terminated at its source in the characteristic impedance of that line. It is highly desirable
that the the source driving the ADC CLK pin only drive that pin. However, if that source is used to drive other
things, each driven pin should be a.c. terminated with a series RC to ground, as shown in Figure 40, such that
the resistor value is equal to the characteristic impedance of the clock line and the capacitor value is
(6)
where tPR is the signal propagation rate down the clock line, "L" is the line length and ZO is the characteristic
impedance of the clock line. This termination should be as close as possible to the ADC clock pin but beyond it
as seen from the clock source. Typical tPD is about 150 ps/inch (60 ps/cm) on FR-4 board material. The units of
"L" and tPD should be the same (inches or centimeters).
Take care to maintain a constant clock line impedance throughout the length of the line. Refer to Application
Note AN-905 (SNLA035) or AN-1113 (SNLA011) for information on setting and determining characteristic
impedance.
OE
The OE pin, when high, puts the output pins into a high impedance state. When this pin is low the outputs are in
the active state. The ADC12020 will continue to convert whether this pin is high or low, but the output can not be
read while the OE pin is high.
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The OE pin should NOT be used to multiplex devices together to drive a common bus as this will result in
excessive capacitance on the data output pins, reducing SNR and SINAD performance of the converter. See
DATA OUTPUTS.
PD
The PD pin, when high, holds the ADC12020 in a power-down mode to conserve power when the converter is
not being used. The power consumption in this state is 40 mW with a 20 MHz clock and the output data pins are
undefined in this mode. The data in the pipeline is corrupted while in the power down mode.
The Power Down Mode Exit Cycle time is determined by the value of the capacitors on pins 30, 31 and 32.
These capacitors loose their charge in the Power Down mode and must be charged by on-chip circuitry before
conversions can be accurate.
DATA OUTPUTS
The ADC12020 has 12 TTL/CMOS compatible Data Output pins. Valid offset binary data is present at these
outputs while the OE and PD pins are low. While the tOD time provides information about output timing, a simple
way to capture a valid output is to latch the data on the falling edge of the conversion clock (pin 10).
Be very careful when driving a high capacitance bus. The more capacitance the output drivers must charge for
each conversion, the more instantaneous digital current flows through VDR and DR GND. These large charging
current spikes can cause on-chip noise that can couple into the analog circuitry, degrading dynamic
performance. Adequate power supply bypassing and careful attention to the ground plane will reduce this
problem. Additionally, bus capacitance beyond that specified will cause tOD to increase, making it difficult to
properly latch the ADC output data. The result could be an apparent reduction in dynamic performance.
To minimize noise due to output switching, minimize the load currents at the digital outputs. This can be done by
connecting buffers (74AC541, for example) between the ADC outputs and any other circuitry. Only one driven
input should be connected to each output pin. Additionally, inserting series resistors of 100Ω at the digital
outputs, close to the ADC pins, will isolate the outputs from trace and other circuit capacitances and limit the
output currents, which could otherwise result in performance degradation. See Figure 40.
While the ADC12020 will operate with VDR voltages down to 1.8V, tOD increases with reduced VDR. Be careful of
external timing when using reduced VDR.
Figure 40. Simple Application Circuit with Single-Ended to Differential Buffer
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511, 1%
75
255, 1%
50:
SIGNAL
INPUT
To ADC
VIN100 pF
+
49.9,
1%
Amplifier:
LMH6550
VCM
280, 1%
-
100
pF
511, 1%
75
+
LMV321
To ADC
VIN+
From ADC
VRM Pin
511, 1%
Figure 41. Differential Drive Circuit of Figure 40
Figure 42. Driving the Signal Inputs with a Transformer
POWER SUPPLY CONSIDERATIONS
The power supply pins should be bypassed with a 10 µF capacitor and with a 0.1 µF ceramic chip capacitor
within a centimeter of each power pin. Leadless chip capacitors are preferred because they have low series
inductance.
As is the case with all high-speed converters, the ADC12020 is sensitive to power supply noise. Accordingly, the
noise on the analog supply pin should be kept below 100 mVP-P.
No pin should ever have a voltage on it that is in excess of the supply voltages, not even on a transient basis. Be
especially careful of this during turn on and turn off of power.
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The VDR pin provides power for the output drivers and may be operated from a supply in the range of 2.35V to
VD (nominal 5V). This can simplify interfacing to 3V devices and systems. DO NOT operate the VDR pin at a
voltage higher than VD.
LAYOUT AND GROUNDING
Proper grounding and proper routing of all signals are essential to ensure accurate conversion. Maintaining
separate analog and digital areas of the board, with the ADC12020 between these areas, is required to achieve
specified performance.
The ground return for the data outputs (DR GND) carries the ground current for the output drivers. The output
current can exhibit high transients that could add noise to the conversion process. To prevent this from
happening, the DR GND pins should NOT be connected to system ground in close proximity to any of the
ADC12020's other ground pins.
Capacitive coupling between the typically noisy digital circuitry and the sensitive analog circuitry can lead to poor
performance. The solution is to keep the analog circuitry separated from the digital circuitry, and to keep the
clock line as short as possible.
Digital circuits create substantial supply and ground current transients. The logic noise thus generated could
have significant impact upon system noise performance. The best logic family to use in systems with A/D
converters is one which employs non-saturating transistor designs, or has low noise characteristics, such as the
74LS, 74HC(T) and 74AC(T)Q families. The worst noise generators are logic families that draw the largest
supply current transients during clock or signal edges, like the 74F and the 74AC(T) families. In high speed
circuits, however, it is often necessary to use these higher speed devices. Best performance requires careful
attention to PC board layout and to proper signal integrity techniques.
The effects of the noise generated from the ADC output switching can be minimized through the use of 47Ω to
100Ω resistors in series with each data output line. Locate these resistors as close to the ADC output pins as
possible.
Since digital switching transients are composed largely of high frequency components, total ground plane copper
weight will have little effect upon the logic-generated noise. This is because of the skin effect. Total surface area
is more important than is total ground plane volume.
Generally, analog and digital lines should cross each other at 90° to avoid crosstalk. To maximize accuracy in
high speed, high resolution systems, however, avoid crossing analog and digital lines altogether. It is important to
keep clock lines as short as possible and isolated from ALL other lines, including other digital lines. Even the
generally accepted 90° crossing should be avoided with the clock line as even a little coupling can cause
problems at high frequencies. This is because other lines can introduce jitter into the clock line, which can lead to
degradation of SNR. Also, the high speed clock can introduce noise into the analog chain.
Best performance at high frequencies and at high resolution is obtained with a straight signal path. That is, the
signal path through all components should form a straight line wherever possible.
Figure 43. Example of a Suitable Layout
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Be especially careful with the layout of inductors. Mutual inductance can change the characteristics of the circuit
in which they are used. Inductors should not be placed side by side, even with just a small part of their bodies
beside each other.
The analog input should be isolated from noisy signal traces to avoid coupling of spurious signals into the input.
Any external component (e.g., a filter capacitor) connected between the converter's input pins and ground or to
the reference input pin and ground should be connected to a very clean point in the analog ground plane.
Figure 43 gives an example of a suitable layout. A single ground plane is recommended with separate analog
and digital power planes. The analog and digital power planes should NOT overlap each other. All analog
circuitry (input amplifiers, filters, reference components, etc.) should be placed over the analog power plane. All
digital circuitry and I/O lines should be placed over the digital power plane. Furthermore, all components in the
reference circuitry and the input signal chain that are connected to ground should be connected together with
short traces and enter the ground plane at a single point. All ground connections should have a low inductance
path to ground.
DYNAMIC PERFORMANCE
To achieve the best dynamic performance, the clock source driving the CLK input must be free of jitter. Isolate
the ADC clock from any digital circuitry with buffers, as with the clock tree shown in Figure 44.
As mentioned in LAYOUT AND GROUNDING, it is good practice to keep the ADC clock line as short as possible
and to keep it well away from any other signals. Other signals can introduce jitter into the clock signal, which can
lead to reduced SNR performance, and the clock can introduce noise into other lines. Even lines with 90°
crossings have capacitive coupling, so try to avoid even these 90° crossings of the clock line.
Figure 44. Isolating the ADC Clock from other Circuitry with a Clock Tree
COMMON APPLICATION PITFALLS
Driving the inputs (analog or digital) beyond the power supply rails. For proper operation, all inputs should
not go more than 100 mV beyond the supply rails (more than 100 mV below the ground pins or 100 mV above
the supply pins). Exceeding these limits on even a transient basis may cause faulty or erratic operation. It is not
uncommon for high speed digital components (e.g., 74F and 74AC devices) to exhibit overshoot or undershoot
that goes above the power supply or below ground. A resistor of about 50Ω to 100Ω in series with any offending
digital input, close to the signal source, will eliminate the problem.
Do not allow input voltages to exceed the supply voltage, even on a transient basis. Not even during power up or
power down.
Be careful not to overdrive the inputs of the ADC12020 with a device that is powered from supplies outside the
range of the ADC12020 supply. Such practice may lead to conversion inaccuracies and even to device damage.
Attempting to drive a high capacitance digital data bus. The more capacitance the output drivers must
charge for each conversion, the more instantaneous digital current flows through VDR and DR GND. These large
charging current spikes can couple into the analog circuitry, degrading dynamic performance. Adequate
bypassing and maintaining separate analog and digital areas on the pc board will reduce this problem.
Additionally, bus capacitance beyond that specified will cause tOD to increase, making it difficult to properly latch
the ADC output data. The result could, again, be an apparent reduction in dynamic performance.
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The digital data outputs should be buffered (with 74ACQ541, for example). Dynamic performance can also be
improved by adding series resistors at each digital output, close to the ADC12020, which reduces the energy
coupled back into the converter output pins by limiting the output current. A reasonable value for these resistors
is 100Ω.
Using an inadequate amplifier to drive the analog input. As explained in Signal Inputs, the capacitance seen
at the input alternates between 8 pF and 7 pF, depending upon the phase of the clock. This dynamic load is
more difficult to drive than is a fixed capacitance.
If the amplifier exhibits overshoot, ringing, or any evidence of instability, even at a very low level, it will degrade
performance. A small series resistor and shunt capacitor at each amplifier output (as shown in Figure 41 and
Figure 42) will improve performance. The LMH6550 , the LMH6702 and the LMH6628 have been successfully
used to drive the analog inputs of the ADC12020.
Also, it is important that the signals at the two inputs have exactly the same amplitude and be exactly 180º out of
phase with each other. Board layout, especially equality of the length of the two traces to the input pins, will
affect the effective phase between these two signals. Remember that an operational amplifier operated in the
non-inverting configuration will exhibit more time delay than will the same device operating in the inverting
configuration.
Operating with the reference pins outside of the specified range. As mentioned in Reference Pins, VREF
should be in the range of
1.0V ≤ VREF ≤ 2.4V
(7)
Operating outside of these limits could lead to performance degradation.
Using a clock source with excessive jitter, using excessively long clock signal trace, or having other
signals coupled to the clock signal trace. This will cause the sampling interval to vary, causing excessive
output noise and a reduction in SNR and SINAD performance.
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REVISION HISTORY
Changes from Revision A (March 2013) to Revision B
•
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 24
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PACKAGE OPTION ADDENDUM
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10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
ADC12020CIVY/NOPB
ACTIVE
LQFP
NEY
32
250
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 85
ADC12020
CIVY
ADC12020CIVYX/NOPB
ACTIVE
LQFP
NEY
32
1000
RoHS & Green
SN
Level-3-260C-168 HR
-40 to 85
ADC12020
CIVY
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
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