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5. Practical folders:
(a) |
(b) |
Fig. 7 (a) The contribution of the fifth amplifier goes unused.
(b)This redundancy is used to reduce the number of preamplifiers
*Vx1 and Vx2 are fixed voltages generated by a single preamplifier shared by all folders.
*Power dissipation ¯.
6.Interpolation with current-mode folder signals
Fig. 8. Interpolation can be used to eliminate half or more of the folder blocks
Fig. 9. Interpolation with current-mode folder signals. A current split-in- four block is shown on the right.
* The number of folders ¯. Þ 16 ® 8
* Problems: (1) It adds an extra node to the signal path, reducing the bandwidth of the folder circuit.
(2) It does not work readily at low power supply voltages.
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*Advantages:
(a)Currents are summed to drive the latch (i.e. IinL + IinR) Þ The input signal has very little effect after latching begins.
(b)IinL and IinR always flow from tracking to latching Þ The folders are little disturbed.
*Need the second-stage buffer and latch.
(2)Second stage:
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9. Measurement results:
Fig. 18. SNDR versus input frequency at 400 Msample/s
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Fig. 19. Die photo
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