Trung tâm đào tạo thiết kế vi mạch Semicon


  • ĐĂNG KÝ TÀI KHOẢN ĐỂ TRUY CẬP NHIỀU TÀI LIỆU HƠN!
  • Đăng ký
    *
    *
    *
    *
    *
    Fields marked with an asterisk (*) are required.
semi1_solvingproblems.jpg

Running Disparity

Email In PDF.
In order to create a DC-balanced data stream, the concept of disparity is employed to balance the number of 0s and 1s. 

The disparity of a block is calculated by the number of 1s minus the number of 0s. The value of a block that has a zero disparity is called disparity neutral. If both the 4-bit and 6-bit blocks are disparity neutral, a combined 10-bit encoded data will be disparity neutral as well. This will create a perfect DC-balanced code. 
However, this is not possible. Because only 6 out of the 16 possible values of the 4-bit block are disparity neutral, they are not enough for encoding the 8 values of the 3-bit block. 
Likewise, only 20 values of the 6-bit block are disparity neutral and they are not enough for encoding the 32 values of the 5-bit block. Because both the 4-bit and 6-bit blocks have an even number of bits, the disparity is not possible to be +1 or -1. Therefore, the values with a disparity of +2 and -2 are also used in the 8b/10b coding scheme. 

Table 1 and Table 2 are the values that are used for the 3-bit to 4-bit encoding and the 5-bit to 6-bit encoding respectively. Concatenating the 4-bit and 6-bit blocks together generates the 10-bit encoded value. Note that some of the encoded values in Table 1 and Table 2 have two possible values, one with a disparity value of +2 and the other with a disparity value of -2. The 8b/10b coding scheme was designed to combine the values of the 4-bit and 6-bit blocks perfectly so that the worst case disparity value of the 10-bit code group will be at most +2 or -2. 

For H G F E D C B A Dx.y a b c d e i f g h j MSB LSB LSB MSB LSB MSB 8b 10b or Kx.y code group 8b/10b Encoder/Decoder 3 example, the 4-bit encoded values with disparity value+2 will not be combined with the 6-bit encoded values with disparity value +2 because this will create a 10-bit value with disparity value +4.

In General , What is running disparity ?
Here is the definition -
Running disparity is the difference between the number of logic 1 bits and logic 0 bits between the start of a data sequence and a particular instant in time during its transmission. The RD for a character is the difference between the number of 1 bits and 0 bits in that character. If there are more 1 bits than 0 bits, the RD is defined as positive. If there are fewer 1 bits than 0 bits, the RD is defined as negative. If the number of 1 bits and 0 bits is the same, the RD is defined as neutral or zero.

As it is said, Running disparity is useful in DC balancing. After encoding 8-bit into 10-bits, few words still have more 1's than 0's or more 0's than 1's. DC balancing can be adjusted based on the running disparity.


So the next question is , How to calculate the running disparity ?
Answer is ,find out the number of 1's and number of 0's in the parallel data and based on the comparison , running disparity can be calculated.

Next question is , How to check the DC balance ?
Answer is , DC balancing is check the number of 1's and 0's in the data stream for a period of time , difference between number of 1's and 0's should not be large, if it is large , it means the encoding is not correctly implemented.
 Bạn Có Đam Mê Với Vi Mạch hay Nhúng      -     Bạn Muốn Trau Dồi Thêm Kĩ Năng

Mong Muốn Có Thêm Cơ Hội Trong Công Việc

Và Trở Thành Một Người Có Giá Trị Hơn

Bạn Chưa Biết Phương Thức Nào Nhanh Chóng Để Đạt Được Chúng

Hãy Để Chúng Tôi Hỗ Trợ Cho Bạn. SEMICON  

 
Lần cập nhật cuối ( Thứ ba, 05 Tháng 10 2021 13:40 )  

CÁC BÀI VIẾT LIÊN QUAN