LTC2335-16 datasheet(28/40 Pages) LINER

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LTC2335-16

233516f

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conversions following an idle period. Figure 12 compares

the burst conversion response of the LTC2335-16 with an

input near full scale for two reference configurations. The

first configuration employs the internal reference buffer

with REFIN externally overdriven by an LTC6655-2.048,

while the second configuration disables the internal ref-

erence buffer and overdrives REFBUF with an external

LTC6655-4.096. In both cases REFBUF is bypassed to

GND with a 47µF ceramic capacitor.

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 LTC2335-16 achieves a typical SNR of 94.4dB in

the ±10.24V range at a 1Msps sampling rate with a true

bipolar 2kHz input signal.

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

throughNthharmonics,respectively.Figure13showsthat

the LTC2335-16 achieves a typical THD of –109dB (N = 6)

in the ±10.24V range at a 1Msps sampling rate with a true

bipolar 2kHz input signal.

applicaTions inForMaTion

Figure 13. 32k Point FFT fSMPL = 1Msps, fIN = 2kHz

Figure 12. Burst Conversion Response of the

LTC2335-16, fSMPL = 1Msps

DYNAMIC PERFORMANCE

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 frequen-

cies outside the fundamental. The LTC2335-16 provides

guaranteed tested limits for both AC distortion and noise

measurements.

Signal-to-Noise and Distortion Ratio (SINAD)

The signal-to-noise and distortion ratio (SINAD) is the

ratio between the RMS amplitude of the fundamental input

frequency and the RMS amplitude of all other frequency

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

to frequencies below half the sampling frequency, exclud-

ing DC. Figure 13 shows that the LTC2335-16 achieves a

typical SINAD of 94.3dB in the ±10.24V range at a 1Msps

sampling rate with a true bipolar 2kHz input signal.

EXTERNAL REFERNCE ON REFBUF

INTERNAL REFERENCE BUFFER

±10.24V RANGE

IN+ = 10V

IN– = 0V

TIME (µs)

100

200

300

400

500

–1

233516 F12

±10.24V RANGE

TRUE BIPOLAR DRIVE (IN– = 0V)

SNR = 94.5dB

THD = –109dB

SINAD = 94.4dB

SFDR = 111dB

FREQUENCY (kHz)

100

200

300

400

500

–180

–160

–140

–120

–100

–80

–60

–40

–20

233516 F13

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