73M2901CE Data Sheet
DS_2901CE_031
8 Modem Performance Characteristics
The curves presented in this data sheet define modem IC performance under a variety of line conditions
typical of those encountered over the Public Switched Telephone Network.
8.1
BER vs. SNR
This test represents the ability of the modem to operate over noisy lines with a minimum amount of data
transfer errors. Since some noise is generated in the best dial up lines, the modem must operate with the
lowest signal to noise ratio (SNR) possible.
Better modem performance is indicated by test curves that are closest to the BER axis. A narrow spread
between curves representing the four line parameters indicates minimal variation in performance while
operating over a range of typical operating conditions. A DPSK or QAM modem will exhibit better BER
performance test curves receiving in the low band (answer mode) than in the high band (originate mode).
8.2
BER vs. Receive Level
This test measures the dynamic range of the modem. Because signal levels vary widely over dial up
lines, the widest possible dynamic range is desirable. The SNR is held constant at the indicated values
as the receive level is lowered from a very high to a very low signal level. The width of the bowl of these
curves, taken at the BER break points is the measure of the dynamic range.
Figure 6: BER vs SNR
Figure 7: BER vs Receive Level
18
Rev. 3.3
TERIDIAN [ TERIDIAN SEMICONDUCTOR CORPORATION ]
