Rainbow Electronics MAX1383 - Manual (Page 20)

Signal-to-Noise Ratio
For a waveform perfectly reconstructed from digital
samples, signal-to-noise ratio (SNR) is the ratio of full-
scale analog input (RMS value) to the RMS quantization
error (residual error). The theoretical minimum analog-
to-digital noise is caused by quantization error, and
results directly from the ADC’s resolution (N bits):
SNR = (6.02 x N + 1.76)dB
In reality, there are other noise sources besides quanti-
zation noise, including thermal noise, reference noise,
clock jitter, etc. Therefore, SNR is computed by taking
the ratio of the RMS signal to the RMS noise, which
includes all spectral components minus the fundamen-
tal, the first five harmonics, and the DC offset.
Signal-to-Noise Plus Distortion
Signal-to-noise plus distortion (SINAD) is the ratio of the
fundamental input frequency’s RMS amplitude to the
RMS equivalent of all other ADC output signals:
SINAD(dB) = 20 x log(SignalRMS/NoiseRMS)
Effective Number of Bits
Effective number of bits (ENOB) indicates the global
accuracy of an ADC at a specific input frequency and
sampling rate. An ideal ADC’s error consists of quanti-
zation noise only. With an input range equal to the full-
scale range of the ADC, calculate the ENOB as follows:
Total Harmonic Distortion
Total harmonic distortion (THD) is the ratio of the RMS
sum of the first five harmonics of the input signal to the
fundamental itself. This is expressed as:
where V
1
is the fundamental amplitude, and V
2
through
V 5 are the amplitudes of the 2nd- through 5th-order
harmonics.
Spurious-Free Dynamic Range
Spurious-free dynamic range (SFDR) is the ratio of the
RMS amplitude of the fundamental (maximum signal
component) to the RMS value of the next largest distor-
tion component.
Full-Power Bandwidth
Full-power bandwidth is the frequency at which the input
signal amplitude attenuates by 3dB for a full-scale input.
Full-Linear Bandwidth
Full-linear bandwidth is the frequency at which the sig-
nal-to-noise plus distortion (SINAD) is equal to 56dB.
Intermodulation Distortion
Any device with nonlinearities creates distortion prod-
ucts when two sine waves at two different frequencies
(f1 and f2) are input into the device. Intermodulation
distortion (IMD) is the total power of the IM2 to IM5
intermodulation products to the Nyquist frequency rela-
tive to the total input power of the two input tones, f1
and f2. The individual input tone levels are at
-6dBFS.
Chip Information
PROCESS: BiCMOS
THD
V V V V
V
= ×
+ + +
⎛
⎝
⎜
⎜
⎞
⎠
⎟
⎟
20
2
2
3
2
4
2
5
2
1
log
ENOB
SINAD
=
− ⎛
⎝⎜ ⎞
⎠⎟
1 76
6 02
.
.
MAX1377/MAX1379/MAX1383
Dual, 12-Bit, 1.25Msps Simultaneous-Sampling
ADCs with Serial Interface
20 ______________________________________________________________________________________
MAX1377
QUADRATURE
TRANSMITTER
DSP
PROCESSING
V L
T/R
QUADRATURE
DEMODULATOR
12-BIT
ADC
DAC
I
DAC
AVDD
Q
12-BIT
ADC
V L
Figure 17. Quadrature Wireless-Communication System