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LTC2328-16

232816fb

For more information www.linear.com/LTC2328-16

applicaTions inForMaTion

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 LTC2328-16 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 from above DC and below half the sampling

frequency. Figure 8 shows that the LTC2328-16 achieves

a typical SINAD of 93.4dB at a 1MHz sampling rate with

a 2kHz 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 8 shows

that the LTC2328-16 achieves a typical SNR of 93.5dB at

a 1MHz sampling rate with a 2kHz 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.

POwER CONSIDERATIONS

The LTC2328-16 provides two power supply pins: the 5V

power supply (VDD), and the digital input/output interface

power supply (OVDD). The flexible OVDD supply allows

the LTC2328-16 to communicate with any digital logic

operating between 1.8V and 5V, including 2.5V and 3.3V

systems.

Power Supply Sequencing

The LTC2328-16 does not have any specific power supply

sequencing requirements. Care should be taken to adhere

to the maximum voltage relationships described in the

Absolute Maximum Ratings section. The LTC2328-16

has a power-on reset (POR) circuit that will reset the

LTC2328-16 at initial power-up or whenever the power

supply voltage drops below 2V. Once the supply voltage

reenters the nominal supply voltage range, the POR will

re-initialize the ADC. No conversions should be initiated

until 200μs after a POR event to ensure the re-initialization

period has ended. Any conversions initiated before this

time will produce invalid results.

TIMING AND CONTROL

CNV Timing

The LTC2328-16 conversion is controlled by CNV. A ris-

ing edge on CNV will start a conversion and power up

the LTC2328-16. Once a conversion has been initiated,

it cannot be restarted until the conversion is complete.

Figure 8. 32k Point FFT of the LTC2328-16

FREQUENCY (kHz)

–180

–60

–40

–20

–80

–100

–120

–140

–160

232816 F08

SNR = 93.5dB

THD = –111dB

SINAD = 93.4dB

SFDR = –115dB

100

200

300

500

400

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