Datasheet

LM97593
SNWS019B –JULY 2007–REVISED APRIL 2013 www.ti.com
Figure 69. F2 GSM frequency response
The complete channel filter response for standard coefficients is shown in Figure 70. Passband flatness is shown
in Figure 71. The complete filter response for GSM coefficients is shown in Figure 72. GSM Passband flatness is
shown in Figure 73.
The mask shown in Figure 72 is derived from the ETSI GSM 5.05 specifications for a normal Basestation
Transceiver (BTS). For interferers, 9dB was added to the carrier to interference (C/I) ratios. For blockers, 9dB
was added to the difference between the blocker level and 3dB above the reference sensitivity level.
Channel Bandwidth vs. Sample Rate
When the LM97593 is used for GSM systems, a bandwidth of about 200kHz is desired. With a sample rate of
52MHz, the total decimation of 192 provides the desired 270.833kHz output sample rate. This output sample rate
in combination with the FIR filter coefficients create the desired channel bandwidth. If the sample rate is
increased to 65MHz, the decimation must also be increased to 65MHz/270.833kHz or 240.
Figure 70. CIC, F1, & F2 STD frequency response
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