LT6201 datasheet(15/20 Pages) LINER

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LTC2314-14

231414f

For more information www.linear.com/2314-14

applicaTions inForMaTion

Signal-to-Noise and Distortion Ratio (SINAD)

Thesignal-to-noiseanddistortionratio(SINAD)istheratiobe-

tweentheRMSamplitudeofthefundamentalinputfrequency

and the RMS amplitude of all other frequency components

at the A/D output. The output is band-limited to frequencies

fromaboveDCandbelowhalfthesamplingfrequency.Figure

14 shows the LTC2314-14 maintains a SINAD above 74dB

up to the Nyquist input frequency of 2.25MHz.

Effective Number of Bits (ENOB)

The effective number of bits (ENOB) is a measurement of

the resolution of an ADC and is directly related to SINAD

by the equation where ENOB is the effective number of

bits of resolution and SINAD is expressed in dB:

ENOB = (SINAD – 1.76)/6.02

At the maximum sampling rate of 5MHz, the LTC2314-14

maintains an ENOB above 12 bits up to the Nyquist input

frequency of 2.25MHz. (Figure 14)

Signal-to-Noise Ratio (SNR)

The signal-to-noise ratio (SNR) is the ratio between the

RMS amplitude of the fundamental input frequency and

the RMS amplitude of all other frequency components

except the first five harmonics and DC. Figure 13 shows

that the LTC2314-14 achieves a typical SNR of 77.5dB at

a 4.5MHz sampling rate with a 500kHz input frequency.

Total Harmonic Distortion (THD)

TotalHarmonicDistortion(THD)istheratiooftheRMSsum

ofallharmonicsoftheinputsignaltothefundamentalitself.

The out-of-band harmonics alias into the frequency band

between DC and half the sampling frequency (fSMPL/2).

THD is expressed as:

THD

=20log

V22

+V32 +V42 +VN2

where V1 is the RMS amplitude of the fundamental fre-

quencyandV2throughVNaretheamplitudesofthesecond

through Nth harmonics. THD versus Input Frequency is

shown in the Typical Performance Characteristics section.

The LTC2314-14 has excellent distortion performance up

to the Nyquist frequency.

Figure 11. LTC2314-14 Transfer Function

INPUT VOLTAGE (V)

231414 F11

111...111

111...110

000...000

000...001

FS – 1LSB

0 1LSB

been digitized 16,384 times. The distribution is Gaussian

and the RMS code transition noise is 0.7LSB. This cor-

responds to a noise level of 77.5dB relative to a full scale

voltage of 4.096V.

Figure 12. Histogram for 16384 Conversions

231414 F12

CODE

8194

8196 8197

8195

8198 8199 8200

σ = 0.7

2000

1000

3000

4000

5000

7000

6000

Dynamic Performance

The LTC2314-14 has excellent high speed sampling

capability. Fast Fourier Transform (FFT) techniques are

used to test the ADC’s frequency response, distortion and

noise at the rated throughput. By applying a low distortion

sine wave and analyzing the digital output using an FFT

algorithm, the ADC’s spectral content can be examined

for frequencies outside the applied fundamental. The

LTC2314-14 provides guaranteed tested limits for both

AC distortion and noise measurements.

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