______________Dynamic Performance

Signal-to-noise and distortion (SINAD) is the ratio of the

fundamental input frequency’s RMS amplitude to all

other ADC output signals. The output spectrum is limit-

ed to frequencies above DC and below one-half the

ADC sample rate.

The theoretical minimum analog-to-digital noise is

caused by quantization error, and results directly from

the ADC’s resolution: SNR = (6.02N + 1.76)dB, where

N is the number of bits of resolution. Therefore, a per-

fect 6-bit ADC can do no better than 38dB.

The FFT Plot (see

Typical Operating Characteristics)

shows the result of sampling a pure 20MHz sinusoid at

a 90MHz clock rate. This FFT plot of the output shows

the output level in various spectral bands. The plot has

been averaged to reduce the quantization noise floor

and reveal the low-amplitude spurs. This emphasizes the

excellent spurious-free dynamic range of the MAX1011.

The effective resolution (or effective number of bits) the

ADC provides can be measured by transposing the

equation that converts resolution to SINAD: N = (SINAD

- 1.76)/ 6.02 (see

Typical Operating Characteristics).

Low-Power, 90Msps, 6-Bit ADC

_______________________________________________________________________________________

9

Figure 9. Ideal Transfer Function

111111

111110

111101

100001

100000

011111

011110

000011

000010

000001

000000

-FSR

2

0

1LSB

INPUT VOLTAGE (IN+ TO IN-)

FSR

2

Figure 8. MAX1011 Timing Diagram

DATA OUT

1.4V

DATA VALID N - 1

DATA VALID N

1.4V

50%

TNK+

(INPUT CLOCK)

DCLK

ANALOG

INPUT

N

N + 1

N + 2