USER’S MANUAL__________________________________________________________________
288 _________________________________________________________________ M211322EN-D
noise terms thus contributes an RMS power that is smaller than the
Peak-to-Noise ratio would imply. In the case of a sinusoidal input, this
gives a 3 dB boost in effective SNR.
- The format, of course, also represents negative amplitudes with the
same relative precision as positive values. In a fixed-point format this
would add 6 dB (one more bit) to the overall dynamic range and
large-signal SNR. In the floating format we really only gain 3 dB (half
a bit) because the RMS noises add independently on the positive and
negative excursions.
- The packed format is used to encode timeseries (I,Q) pairs, and it's the
SNR properties of these pairs that we're really concerned about. To a
first approximation, having a pair of values roughly doubles the
information content and adds another 3dB to the SNR.
The last of the three time series output words, the "Log of Power in
Sample", is provided mainly for backwards compatibility. It can be
calculated from the I and Q numbers. To convert to dBm it requires a slope
and offset as follows:
where:
P
MAX
= +4.5dBm for 12-bit IFDR, +6.0 dBm for 14-bit IFDR
V
MAX
= 0.5309 Volts for 12-bit IFDR, 0.6310 V for 14-bit IFDR
Slope = "Log Power Slope" word 3 of SOPRM command. 0.03
recommended.
For backwards compatibility, the RVP900 produces a 8-bit fixed point
time series format. Because of the limited dynamic range available, this
will only show strong signals, and is not recommended for use. The I, Q,
and Log power triplets are packed into two 16-bit output words as follows:
0916-115
The "Log Power" value is the upper 8 bits of the long format. The other
numbers are produced by the equation:
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