LTC1604ACG datasheet(16/20 Pages) LINER

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LTC1604

APPLICATIONS INFORMATION

1604 F16

AIN

VSS

OVDD

DGND

AVDD

LTC1604

DIGITAL

SYSTEM

ANALOG

INPUT

CIRCUITRY

AGND

5 TO 8

DVDD

OGND

REFCOMP

µF

VREF

2.2

µF

AIN

–

µF

AVDD

µF

–

µF

DC PERFORMANCE

The noise of an ADC can be evaluated in two ways: signal-

to-noise raio (SNR) in frequency domain and histogram in

time domain. The LTC1604 excels in both. Figure 18a

demonstrates that the LTC1604 has an SNR of over 90dB

in frequency domain. The noise in the time domain histo-

gram is the transition noise associated with a high resolu-

tion ADC which can be measured with a fixed DC signal

applied to the input of the ADC. The resulting output codes

are collected over a large number of conversions. The

shape of the distribution of codes will give an indication of

the magnitude of the transition noise. In Figure 17 the

distribution of output codes is shown for a DC input that

has been digitized 4096 times. The distribution is Gaussian

and the RMS code transition noise is about 0.66LSB. This

corresponds to a noise level of 90.9dB relative to full scale.

Adding to that the theoretical 98dB of quantization error

for 16-bit ADC, the resultant corresponds to an SNR level

of 90.1dB which correlates very well to the frequency

domain measurements in DYNAMIC PERFORMANCE

section.

DYNAMIC PERFORMANCE

The LTC1604 has excellent high speed sampling capabil-

ity. Fast fourier transform (FFT) test techniques are used

to test the ADC’s frequency response, distortions 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 fundamental. Figures 18a and 18b

show typical LTC1604 FFT plots.

CODE

–5 –4 –3 –2 –1 0

2500

2000

1500

1000

500

1604 F17

Figure 17. Histogram for 4096 Conversions

FREQUENCY (kHz)

–60

–40

–20

1604 F18a

–80

–100

80 100 120 140 160

–120

–140

fSAMPLE = 333kHz

fIN = 4.959kHz

SINAD = 90.2dB

THD = –103.2dB

Figure 18a. This FFT of the LTC1604’s Conversion of a

Full-Scale 5kHz Sine Wave Shows Outstanding Response

with a Very Low Noise Floor When Sampling at 333ksps

Figure 16. Power Supply Grounding Practice

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