73M1903C-EVM Maxim Integrated Products, 73M1903C-EVM Datasheet - Page 26

• Manufacturer Part Number: 73M1903C-EVM
• Description: BOARD DEMO 73M1903C WORLDWIDE
• Manufacturer: Maxim Integrated Products

Specifications of 73M1903C-EVM

• Main Purpose: Interface, Analog Front End (AFE)
• Utilized Ic / Part: *
• Primary Attributes: *
• Secondary Attributes: *
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Embedded: -

73M1903C Data Sheet
6.6
A differential receive signal applied at the RXAP and RXAN pins. The DC bias for the RXAP/RXAN
inputs is supplied from TXAP/TXAN thru the external DAA in normal conditions. It can be supplied
internally, in the absence of the external DAA, by setting RXPULL bit in Register02.
The receive signal goes into a second-order continuous time, Sallen-Key, low-pass filter (AAF) with a 3
dB point at approximately 40 kHz. The filtered output signal is the input to an analog sigma-delta
modulator (ASDM), clocked at an over sampling frequency of 1.536 MHz for Fs = 8 kHz, which converts
the analog signal to a serial bit stream with a pulse density that is proportional to the amplitude of the
analog input signal.
There are three gain control bits for the receive path. The RXGAIN bit in control register one results in a
+20 dB gain of the receive signal when set to 1. This 20 dB of gain compensates for the loss through the
DAA while on hook and is used for Caller ID reception. This gain is realized in the front end of ASDM.
The other gain bits in control register 1, RXG1:0, compensate for differences in loss through the receive path.
The output of ASDM is a serial bit stream that feeds multiple digital sinc
synchronized so that there is one sample available after every 96 analog samples or at a rate of 16 kHz
for Fs=8 kHz. The output of the sinc
amplitude of the input signal. The sinc
a droop in the passband that is later corrected for by a 48-tap FIR filter that follows.
The output of the sinc
correction as well as rejecting noise above Fs/2 or 4 kHz for Fs=8 kHz. The output of this filter is then
decimated by a factor of 2; so, the final output is 16 bit, two’s compliment samples at a rate of 8 kHz.
Figure 10 and Figure 11 depict the sinc
FIR response that compensates for it and the resulting overall response of the receiver.
26
Modem Receiver
Figure 10: Overall Receiver Frequency Response at 8 kHz Sample Rate
3
filter is input to another 48 tap digital FIR filter that provides an amplitude
RXG1
0
0
1
1
3
filter is a 17 bit, two’s compliment number representing the
3
3
filter, by virtue of holding action (for 96 sample period), introduces
Table 11: Receive Gain
filter’s frequency response of ASDM along with the 48 tap digital
RXG0
0
1
0
1
Receive Gain Setting
12 dB
6 dB
9 dB
0 dB
3
filters. The filters are
DS_1903C_033
Rev. 5.0