TDA8768A Datasheet, PDF (24/32 Pages) NXP Semiconductors – 12-bit, 70 Msps Analog-to-Digital Converter (ADC)

Philips Semiconductors
TDA8768A
12-bit, 70 Msps Analog-to-Digital Converter (ADC)
12.1.2 Dynamic parameters (single tone)
Figure 26 shows the spectrum of a full-scale input sine wave with frequency f_t,
conforming to coherent sampling (f_t/f_s = M/N, where M is the number of cycles and N
is number of samples, M and N being relatively prime), and digitized by the ADC
under test.
magnitude
a1
FCE710
SFDR
a2
s
a3
ak
Fig 26. Spectrum of full-scale input sine wave with frequency f_t.
measured output range
fs/2
Remark: in the following equations, P_noise is the power of the terms which include the
effects of random noise, non-linearities, sampling time errors, and “quantization
noise”.
Signal-to-noise and distortion (SINAD): The ratio of the output signal power to the
noise plus distortion power for a given sample rate and input frequency, excluding the
DC component:
SINAD[db] = 10log _P----_n---_o---_i--_s-^P-_e---^s₊--ⁱ--^gd---ⁿⁱ--_s-^a-_t-^l-_o---_r--_t-_i--_o---_n-
Effective Number of Bits (ENOB): It is derived from SINAD and gives the
theoretical resolution an ideal ADC would require to obtain the same SINAD
measured on the real ADC. A good approximation gives:
ENOB = (SINAD[dB] – (1 ⋅ 76)) ⁄ (6 ⋅ 02)
Total Harmonic Distortion (THD): The ratio of the power of the harmonics to the
power of the fundamental. For k-1 harmonics the THD is:
THD[dB] = 10log ^P----^h-_P--^a--_s-^r-_i-^m-_g---_no---_an---_li-^c---^s
where
P_harmonics
=
a
2
2
+
a
2
3
+
a
2
k
P_signal
=
a
2
1
The value of k is usually 6 (i.e. calculation of THD is done on the first 5 harmonics).
9397 750 09656
Product data
Rev. 02 — 03 July 2002
© Koninklijke Philips Electronics N.V. 2002. All rights reserved.
24 of 32