Digital Decode & Correction Logic Preliminary design review PAYAL DAVE
Outline Introduction Why Digital Decode & Error correction logic requires Main Block diagram Individual block explanation Sims result Conclusion
A7 B7 A6 B6 A5 B5 D7 D6 D5
Need for Digital Decode & Error Correction To eliminate the redundancy of ½ bit in each stage Digital correction takes raw output data of the ADC as input and outputs the digital representation. Error correction logic circuitry takes 14 bit input from ADC stages and eliminated the redundancy of ½ bit in each stage and gives 8 bit digital output. Digital circuits are fast and take low power.
How it is done? Requirements: Implementation: Align ADC (comparator) decisions Correct ADC output bit pattern Add digital data in a 1.5-bit fashion Output a 8-bit digital word Implementation: Shift register using Delayed D flip flop Ripple carry adder
Main Block Diagram SHIFT REGISTER Ripple Carry Adder Output register CLK1 SHIFT REGISTER CLK2 Ripple Carry Adder CLK2 Output register D7 D6 D5 D4 D3 D2 D1 D0
Shift register to align ADC decisions STG -1 STG -2 STG -3 STG -4 STG -5 STG -6 STG -7 DFF CLK1 DFF DFF CLK2 Shift register using D flipflop CLK1 DFF CLK2 DFF DFF DFF DFF DFF CLK1 CLK2 DFF DFF DFF DFF DFF DFF DFF CLK1 CLK2 DFF DFF DFF DFF DFF DFF DFF RIPPLE CARRY ADDER
SHIFT REGISTER TEST BENCH
ALIGNING OF 14 BITS WITHIN 31/2 CLK
Digital correction logic B7 STAGE - 1 STAGE - 2 A6 B6 A5 B5 STAGE - 3 A4 B4 STAGE -4 Concept of Digital Correction A3 B3 STAGE - 5 A2 B2 STAGE -6 A1 B1 STAGE 7 + D7 D6 D5 D4 D3 D2 D1 D0 * * Z = D Y = B XOR C X = A + BC (CARRY BIT) * A B C D + X Y Z Mathematical analysis Of Digital Correction
Logic Equations used for RCA Total gate delay for RCA D0 = B1 C0 = A2 + A1B2 D1 = A1 XOR B2 C1 = B3C0 + A3 D2 = C0 XOR B3 C2 = B4C1 + A4 D3 = C1 XOR B4 C3 = B5C2 + A5 D4 = C2 XOR B5 C4 = B6C3 + A6 D5 = C3 XOR B6 D6 = C4 XOR B7 D7 = B7C4 + A7
RIPPLE CARRY ADDER CARRY BIT A + BC
SS With worst case for 4.5v & 85C
The delay in SS with worst case is
SIMS RESULTS FOR DIFFERENT CORNERS FOR RCA 5.5 v TT SS FS FF SF 5.0v 4.5v 27 85 27 85 27 85 3.97n 4.65n 4.26n 4.63n 5.44n 4.94n 5.38n 6.34n 3.70n 4.73n 4.02n 2.69n 2.89n 3.36n 3.92n 4.60n
ALIGNING OF 14 BITS WITHIN 31/2 CLK
Error Correction Logic A7B7 A6B6 A5B5 A4B4 A3B3 A2B2 A1B1 D7 D6 D5 D4 D3 D2 D1 D0 01 1 1 1 1 1 1 1 1 10 0 0 0 0 0 0 0 0 11 0 0 0 0 0 0 0 1 0 1 1 1 1 1 1 0 0 1 1 1 1 1 0 1
SHIFT REGISTER WITH RCA AND OUTPUT REGISTER RCA WITH OUTPUT REG
Pulse width linear input to shift reg
Conclusion 14 bits coming from the comparator are aligning with the help of the shift register within 41/2 clock cycle. Ripple carry adder takes 6.34ns for worst case condition which is fast enough to get desired output Error correction logic is working for different combination of input bits.