參數(shù)資料
型號(hào): LTC1277IS
廠商: LINEAR TECHNOLOGY CORP
元件分類: ADC
英文描述: Pressure Transducer, Series 19 mm, Compensated, Pressure Range: 0 psi to 5 psi, Gage, 1/4-18 NPT, 10 Vdc excitation
中文描述: 1-CH 12-BIT SUCCESSIVE APPROXIMATION ADC, PARALLEL ACCESS, PDSO24
封裝: 0.300 INCH, PLASTIC, SO-24
文件頁(yè)數(shù): 12/20頁(yè)
文件大?。?/td> 411K
代理商: LTC1277IS
12
LTC1274/LTC1277
APPLICATIO
S I
FOR
ATIO
U
quency is shown in Figure 4. The ADCs have good distor-
tion performance up to the Nyquist frequency and beyond.
W
U
U
Full-Power and Full-Linear Bandwidth
The full-power bandwidth is that input frequency at which
the amplitude of the reconstructed fundamental is re-
duced by 3dB for a full-scale input signal.
The full-linear bandwidth is the input frequency at which
the S/(N + D) has dropped to 68dB (11 effective bits). The
LTC1274/LTC1277 have been designed to optimize input
bandwidth, allowing ADCs to undersample input signals
with frequencies above the converter’s Nyquist frequency.
The noise floor stays very low at high frequencies;
S/(N + D) becomes dominated by distortion at frequencies
far beyond Nyquist.
Driving the Analog Input
The analog input of the LTC1274/LTC1277 is easy to
drive. It draws only one small current spike while charg-
ing the sample-and-hold capacitor at the end of conver-
sion. During conversion the analog input draws only a
small leakage current. The only requirement is that the
amplifier driving the analog input must settle after the
small current spike before the next conversion starts.
Any op amp that settles in 2
μ
s to small current transients
will allow maximum speed operation. If slower op amps
are used, more settling time can be provided by increasing
the time between conversions. Suitable devices capable of
driving the ADC A
IN
input include the LT
1006, LT1007,
LT1220, LT1223 and LT1224 op amps.
Intermodulation Distortion
If the ADC input signal consists of more than one spectral
component, the ADC transfer function nonlinearity can pro-
duce intermodulation distortion (IMD) in addition to THD.
IMD is the change in one sinusoidal input caused by the
presence of another sinusoidal input at a different frequency.
If two pure sine waves of frequencies fa and fb are applied
to the ADC input, nonlinearities in the ADC transfer func-
tion can create distortion products at sum and difference
frequencies of mfa
±
nfb, where m and n = 0, 1, 2, 3, etc.
For example, the 2nd order IMD terms include (fa + fb) and
(fa – fb) while the 3rd order IMD terms include (2fa + fb),
(2fa – fb), (fa + 2fb) and (fa – 2fb). If the two input sine
waves are equal in magnitude, the value (in decibels) of the
2nd order IMD products can be expressed by the following
formula:
IMD (fa ± fb) = 20logAmplitude at (fa ± fb)
Amplitude at fa
Figure 5 shows the IMD performance at a 97kHz input.
Peak Harmonic or Spurious Noise
The peak harmonic or spurious noise is the largest spec-
tral component excluding the input signal and DC. This
value is expressed in decibels relative to the RMS value of
a full scale input signal.
Figure 4. Distortion vs Input Frequency
Figure 5. Intermodulation Distortion
FREQUENCY (Hz)
0
A
0
–20
–40
–60
–80
–100
–120
10k
20k
30k
40k
LTC1274/77 F05
50k
2fb – fa
2fa – fb
fb
fb – fa
fa
2fb
2fa
3fb
2fb + fa
2fa + fb
fa + fb
3fa
f
SAMPLE
= 100kHz
fa = 96.948kHz
fb = 97.681kHz
THD
INPUT FREQUENCY (Hz)
10k
D
0
–20
–40
–60
–80
–100
–120
100k
1M
2M
LTC1274/77 F04
3RD HARMONIC
2ND HARMONIC
f
SAMPLE
= 100kHz
相關(guān)PDF資料
PDF描述
LTC1274 12-Bit, 10mW, 100ksps ADCs with 1uA Shutdown
LTC1274IS Replaced by TLC2933A : High Performance Phase Locked Loop 14-TSSOP -20 to 75
LTC1277CS 12-Bit, 10mW, 100ksps ADCs with 1uA Shutdown
LTC1275AC Phase Locked Loop 14-TSSOP -20 to 75
LTC1276BC 12-Bit, 300ksps Sampling A/D Converters with Reference
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