LTC6652 datasheet(28/50 Pages) LINER

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LTC2373-18

237318f

For more information www.linear.com/LTC2373-18

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 from above DC and below half the sampling

frequency. Figure 15 shows that the LTC2373-18 achieves

a typical SINAD of 100dB (fully differential) at a 1MHz

sampling rate with a 1kHz input.

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 15 shows

thattheLTC2373-18achievesatypicalSNRof100dB(fully

differential) at a 1MHz sampling rate with a 1kHz input.

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 +…+ VN

where V1 is the RMS amplitude of the fundamental

frequency and V2 through VN are the amplitudes of the

second through Nth harmonics. Figure 15 shows that

the LTC2373-18 achieves a typical THD of –114dB (fully

differential) at a 1MHz sampling rate with a 1kHz input.

applicaTions inForMaTion

Figure 15. 32k Point FFT fSMPL = 1Msps, fIN = 1kHz

FREQUENCY (kHz)

–20

237318 F15

–180

–100

–140

–160

–120

–80

–60

–40

100

200

300

400

500

SNR = 100.7dB

THD = –114dB

SINAD = 100.5dB

SFDR = 115.3dB

Figure 14a. Transient Response of the LTC2373-18 in the

Fully Differential Input Range

Figure 14c. Transient Response of the LTC2373-18 in the

Pseudo-Differential Bipolar Input Range

Figure 14b. Transient Response of the LTC2373-18 in the

Pseudo-Differential Unipolar Input Range

TIME (µs)

–2

100 200 300 400 500 600 700 800 900 1000

237318 F11c

INTERNAL REFERENCE BUFFER

EXTERNAL SOURCE ON REFBUF

TIME (µs)

–2

100 200 300 400 500 600 700 800 900 1000

237318 F14b

INTERNAL REFERENCE BUFFER

EXTERNAL SOURCE ON REFBUF

TIME (µs)

–4

–2

–6

100 200 300 400 500 600 700 800 900 1000

237318 F14c

INTERNAL REFERENCE BUFFER

EXTERNAL SOURCE ON REFBUF

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