參數(shù)資料
型號(hào): 73M1903-IGV
廠商: MAXIM INTEGRATED PRODUCTS INC
元件分類: 消費(fèi)家電
英文描述: SPECIALTY CONSUMER CIRCUIT, PQFP32
封裝: TQFP-32
文件頁數(shù): 36/45頁
文件大?。?/td> 449K
代理商: 73M1903-IGV
73M1903
Modem Analog Front End
DATA SHEET
Page: 41 of 45
2005 TERIDIAN Semiconductor Corporation
Rev 1.4
Example 2: Fxtal = 18.432MHz, Fref = 2.304 MHz.
Pdvsr = Integer [Fxtal/Fref] = 8 = 8h;
Prst[2:0] = 1- 1 = 0 from Fref/Fxtal = 18.432/2.304 = 8/1;
Pseq = {x,x,x,x,x,x,x,x} = xxh
Example 3: Fxtal = 24.576MHz, Fref = 2.4576MHz.
Pdvsr = Integer [ Fxtal/Fref] = 10 = Ah;
Prst[2:0] = 1- 1 = 0 from Fref/Fxtal = 24.576/2.4576 = 10/1;
Pseq = {x,x,x,x,x,x,x,x} = xxh
It is also important to note that when Fxtal/Fref is an integer the output of the pre-scaler is a straight
frequency divider (example 2). As such there will be no jitter generated at Fref. However if Fxtal/Fref is
a fractional number, Fref, at the output of the pre-scaler NCO would be exact only in an average sense
(example 1) and there will be a certain amount of fixed pattern (repeating) jitter associated with Fref which
can be filtered out by the PLL that follows by appropriately programming the PLL. It is important to note,
however, that the fixed pattern jitter does not degrade the performance of the sigma delta modulators so
long as its frequency is >> 4kHz.
PLL
VCO
Kvco
NCO
Prescaler
PFD
Charge
Pump
NCO
Kd
Up
Dn
R1
C1
C2
Divide
by 2/1
Ichp Control
3
Fref
Kvco Control
Figure B-2 PLL Block Diagram
1903B has a built in PLL circuit to allow an operation over wide range of Fs. It is of a conventional design
with the exception of an NCO based feedback divider. (See Figure B-2: PLL Block Diagram).
The architecture of the 73M1903 dictates that the PLL output frequency, Fvco, be related to the sampling
rate, Fs, by Fvco = 2 x 2304 x Fs. The NCO must function as a divider whose divide ratio equals
Fref/Fvco.
Just as in the NCO pre-scaler, a set of three numbers– Ndvsr ( 7 bits ), Nrst ( 3 bits ) and Nseq ( 8 bits )
must be entered thru a serial port to effect this divide:
Ndvsr = Integer [ Fref/Fxtal ] ;
Nrst = Denominator of the ratio (Fvco/Fref), Dnco1, minus 1, when it is expressed as a ratio of two
smallest integers = Nnco1/Dnco1;
Nseq = Divide Sequence
Example 1: Fs = 7.2kHz or Fvco = 2 x 2304 x 7.2kHz =33.1776MHz, Fref = 1.728MHz.
Ndvsr = Integer [ Fvco/Fref ] = 19
Nrst = 5 – 1 = 4 from Fvco/Fref = 19.2 = 96/5;
Nseq =
÷19, ÷19, ÷19, ÷19, ÷20 => {0,0,0,0,1} =xxx00001 = 01h.
相關(guān)PDF資料
PDF描述
73M1903-IM SPECIALTY CONSUMER CIRCUIT, QCC32
73M1903-IM/F SPECIALTY CONSUMER CIRCUIT, PQCC32
73M1903-IMR/F SPECIALTY CONSUMER CIRCUIT, PQCC32
73M1903-IVT/F SPECIALTY CONSUMER CIRCUIT, PDSO20
73M1903-IVTR/F SPECIALTY CONSUMER CIRCUIT, PDSO20
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