參數資料
型號: 73M1903C-IM/F
廠商: Maxim Integrated Products
文件頁數: 37/48頁
文件大小: 0K
描述: IC MODEM AFE MULTIREGIONAL 32QFN
產品培訓模塊: Lead (SnPb) Finish for COTS
Obsolescence Mitigation Program
標準包裝: 490
通道數: 2
電壓 - 電源,模擬: 3 V ~ 3.6 V
電壓 - 電源,數字: 3 V ~ 3.6 V
封裝/外殼: 32-VFQFN 裸露焊盤
供應商設備封裝: 32-QFN(5x5)
包裝: 管件
73M1903C Data Sheet
DS_1903C_033
42
Rev. 5.0
Appendix B
Crystal Oscillator
The crystal oscillator is designed to operate over wide choice of crystals (from 4.9 MHz to 27 MHz). The
crystal oscillator output is the input to an NCO based pre-scaler (divider) prior to being passed onto an
on-chip PLL. The intent of the pre-scaler is to convert the crystal oscillator frequency, Fxtal, to a
convenient frequency to be used as a reference frequency, Fref, for the PLL. A set of three numbers–
Pdvsr (5 bit), Prst (3 bit) and Pseq (8 bit) must be entered thru the serial port as follows:
Pdvsr = Integer [Fref/Fxtal];
Prst = Denominator of the ratio (Fref/Fxtal) minus 1 when it is expressed as a ratio of two smallest
integers = Nnco1/Dnco1;
Pseq = Divide Sequence
Fxtal
mux
count ctrl
overflow
Counter
Pdvsr
Pdvsr +1
Sequence
Register
Rst
Sequence
Counter
Fref
Pseq[7:0]
Prst[2:0]
Figure 20: NCO Block Diagram
Please note that in all cases, pre-scaler should be designed such that pre-scaler output frequency, Fref,
is in the range of 2 ~ 4 MHz.
In the first example below, the exact divide ratio required is Fxtal/Fref = 15.625 =125/8. If a divide
sequence of {
÷16,÷16,÷15,÷16,÷16,÷15,÷16,÷15} is repeated, the effective divide ratio would be exactly
15.625. Consequently, Pdvsr of 15, the length of the repeating pattern, Prst = 8 –1 =7, and the pattern,
{1,1,0,1,1,0,1,0}, where 0 means Pdvsr, or
÷15, and 1 means Pdvsr +1, or ÷16 must be entered as below.
Example 1: Fxtal = 27 MHz, Fref = 1.728 MHz.
Pdvsr = Integer [Fxtal/Fref] = 15 =0Fh
Prst[2:0] = 8 – 1 = 7 from Fxtal/Fref = 15.625 =125/8;
Pseq =
÷16,÷16,÷15,÷16,÷16,÷15,÷16,÷15 => {1,1,0,1,1,0,1,0} =DAh.
In the second exam ple, Fxtal/Fref =4.0. This is a constant divide by 4. Thus, Pdvsr is 4, Prst = 1 –
1 =0 and Pseq = {x,x,x,x,x,x,x,x).
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