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Digital Decode & Correction Logic
Preliminary design review PAYAL DAVE
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Outline Introduction Why Digital Decode & Error correction logic requires Main Block diagram Individual block explanation Sims result Conclusion
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A7 B7 A6 B6 A5 B5 D7 D6 D5
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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.
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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
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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
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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
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SHIFT REGISTER TEST BENCH
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ALIGNING OF 14 BITS WITHIN 31/2 CLK
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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 + D D D D D D D D0 * * Z = D Y = B XOR C X = A + BC (CARRY BIT) * A B C D + X Y Z Mathematical analysis Of Digital Correction
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Logic Equations used for RCA
Total gate delay for RCA D0 = B1 C0 = A2 + A1B D1 = A1 XOR B2 C1 = B3C0 + A D2 = C0 XOR B3 C2 = B4C1 + A D3 = C1 XOR B4 C3 = B5C2 + A D4 = C2 XOR B5 C4 = B6C3 + A D5 = C3 XOR B6 D6 = C4 XOR B7 D7 = B7C4 + A7
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RIPPLE CARRY ADDER CARRY BIT A + BC
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SS With worst case for 4.5v & 85C
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The delay in SS with worst case is
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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
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ALIGNING OF 14 BITS WITHIN 31/2 CLK
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Error Correction Logic
A7B7 A6B6 A5B5 A4B4 A3B3 A2B2 A1B1 D7 D6 D5 D4 D3 D2 D1 D0 01 10 11
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SHIFT REGISTER WITH RCA AND OUTPUT REGISTER
RCA WITH OUTPUT REG
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Pulse width linear input to shift reg
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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.
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