LTC2208CUP-14 Linear Technology, LTC2208CUP-14 Datasheet - Page 25

• Manufacturer Part Number: LTC2208CUP-14
• Description: IC ADC 14BIT 130MSPS 64-QFN
• Manufacturer: Linear Technology

Specifications of LTC2208CUP-14

• Number Of Bits: 14
• Sampling Rate (per Second): 130M
• Data Interface: Parallel
• Number Of Converters: 1
• Power Dissipation (max): 1.78W
• Voltage Supply Source: Single Supply
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 64-WFQFN, Exposed Pad
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

APPLICATIONS INFORMATION
PC BOARD
Figure 14. Derandomizing a Randomized Digital Output
LTC2208-14
ANALOG
INPUT
CLKOUT
D13/D0
D12/D0
AIN
AIN
D2/D0
D1/D0
OF
D0
+
–
LTC2208-14
Figure 15. Functional Equivalent Block Diagram of Internal Dither Circuit
CLOCK/DUTY
ENC
CONTROL
AMP
FPGA
S/H
CYCLE
+
ENC
–
•
•
•
D13
D12
D2
D1
D0
220814 F14
PRECISION
PIPELINED
ADC CORE
14-BIT
DAC
Internal Dither
The LTC2208-14 is a 14-bit ADC with a very linear transfer
function; however, at low input levels even slight imperfec-
tions in the transfer function will result in unwanted tones.
Small errors in the transfer function are usually a result
of ADC element mismatches. An optional internal dither
mode can be enabled to randomize the input location on
the ADC transfer curve, resulting in improved SFDR for
low signal levels.
As shown in Figure 15, the output of the sample-and-hold
amplifi er is summed with the output of a dither DAC. The
dither DAC is driven by a long sequence pseudo-random
number generator; the random number fed to the dither
DAC is also subtracted from the ADC result. If the dither
DAC is precisely calibrated to the ADC, very little of the
dither signal will be seen at the output. The dither signal
that does leak through will appear as white noise. The dither
DAC is calibrated to result in less than 0.5dB elevation in
the noise fl oor of the ADC, as compared to the noise fl oor
with dither off.
SUMMATION
DIGITAL
PSEUDO-RANDOM
HIGH = DITHER ON
LOW = DITHER OFF
MULTIBIT DEEP
DITHER ENABLE
GENERATOR
NUMBER
DRIVERS
OUTPUT
DITH
220814 F15
LTC2208-14
CLKOUT
D13
D0
OF
•
•
•
25
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