Tektronix TDSDDM1, User Manual, Page: 72 / 102

Measurement Descriptions
3–30
TDSDDM1 Disk Drive Measurement Application User Manual
Signal-to-Noise Ratio, SNR
The signal-to-noise ratio measurement, SNR, determines the ratio of the variance
of the readback signal to readback noise. The measured noise consists of media
noise, crosstalk, electronic noise, and other noise types characteristic to disk
drives. Electronic readback noise effects can be mitigated by the averaging
operation performed by the SNR measurement.
Figure 3–19: SNR measurement
Signal-to-noise ratio is defined in terms of variances of the signal and noise, and
thus is independent of DC offsets of the readback voltage. The SNR measure-
ment algorithm assumes that the acquired signal consists of a periodic signal and
independent additive noise. The noise is assumed to be responsible for all the
nonperiodic behavior of the acquired waveform. Noise samples are assumed to
be independent and identically distributed. The SNR measurement is defined as
follows:
SNR
+
10 log
10
ǒ
s
2
s
s
2
n
Ǔ
Definition