TDA8769 datasheet(22/28 Pages) PHILIPS

22 / 28 page

2003 Dec 09

Philips Semiconductors

Objective speciﬁcation

12-bit, 60/80/105 Msps Analog-to-Digital Converter

(ADC) Nyquist/high IF sampling

TDA8769

11.5.2.1

Signal-to-noise and distortion (SINAD)

SINAD is the ratio of the signal power to the noise plus

distortion power, excluding the DC component, at a given

sample rate and input frequency:

dB.

11.5.2.2

Effective number of bits (ENOB)

ENOB is derived from SINAD and gives the theoretical

resolution an ideal ADC would require to obtain the same

SINAD measured on the actual ADC. A good

approximation is:

11.5.2.3

Total harmonic distortion (THD)

THD is the ratio of the power of the harmonics to the power

of the signal frequency. The equation for k

− 1 harmonics

is:

where:

As usual the value of k = 6 (i.e. the calculation of THD is

done with the first 5 harmonics).

11.5.2.4

Signal-to-noise ratio (SNR)

SNR is the ratio of the signal power to the noise power,

excluding the harmonics and DC component of the signal:

11.5.2.5

Spurious free dynamic range (SFDR)

The SFDR specifies the available signal range as the

spectral distance between the amplitude of the

fundamental and the amplitude of the largest spurious

signal, harmonic and non-harmonic, excluding the

DC component.

11.5.2.6

Intermodulation distortion (IMD2 and IMD3)

Figure 16 shows the spectral analysis of a dual tone sine

wave input, at frequencies ft1 and ft2, meeting the

coherence criterion.

The 2nd and 3rd order intermodulation distortion products,

IMD2 and IMD3 respectively, are defined with a dual tone

input. IMD2 is defined as the ratio of the RMS value of

either tone to the RMS value of the second order

intermodulation product, IMD3 with the third order

intermodulation product. The IMD is given by:

SINAD

10log

signal

noise + distortion

--------------------------------------





ENOB

SINAD

1.76

–

6.02

-------------------------------------

THD

10log

harmonics

signal

-------------------------





harmonics

...

signal

SNR

10log

signal

noise

----------------





SFDR

10log

max s

()

--------------------





IMD

10log

intermod

signal

---------------------





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