FX919B Datasheet, PDF (29/47 Pages) CML Microcircuits – Excellent Radio Fading Performance

4-Level FSK Modem Data Pump
FX919B
1.5.7 Transmitted Symbol Shape
Bit 4 of the Command Register (TXIMP) affects the transmit baseband signal and the receive signal
equalisation as follows.
If the TXIMP bit is '0', then the transmit baseband signal is generated by feeding full-width 4-level symbols into
the RRC lowpass filter, and the receive signal equalisation is optimised for this type of signal. With this setting
the FX919B is compatible with FX919A devices.
If the TXIMP bit is set to '1', then impulses, rather than full-width symbols, are fed into the RRC filter when in Tx
mode, and the receive signal equalisation is suitably adjusted in Rx mode.
Figure 15a Input Signal to RRC Filter inTx Mode for TXIMP = 0 and 1
Figure 15b Tx Signal Eye TXIMP = 0
Figure 15c Tx Signal Eye TXIMP = 1
Note that setting TXIMP to '1' affects the Tx output signal level as shown in section 1.7.1 and the table below:
Nominal voltage difference between continuous '+3' and
continuous '-3' symbol outputs.
TXIMP = 0
0.157 V_DD
TXIMP = 1
0.157 V_DD
Nominal Vp-p for continuous '+3 +3 -3 -3..' symbol
pattern
0.20 V_DD
0.22 V_DD
© 1997 Consumer Microcircuits Limited
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D/919B/1