Ripple Counter Cascaded for 8-Bit Count
Low-power interval timers and deep frequency dividers often string together basic asynchronous counting blocks to extend their range. Cascading two 4-bit ripple counters yields an 8-bit asynchronous counter, doubling the resolution at the cost of increased cumulative propagation delay.
The circuit requires an 8-bit output Q generated from a single external clock clk and an active-low asynchronous reset rst_n. The lower nibble Q[3:0] is produced by the first 4-bit ripple counter stage. The upper nibble Q[7:4] must be produced by a second 4-bit ripple counter stage. The clock input of the second stage must be driven by the most significant bit of the first stage to ensure the count cascades correctly every 16 clock cycles.
| rst_n | clk | Q (decimal) | |---------|-------|---------------| | 0 | X | 0 | | 1 | ↑ | Q + 1 |
Constraints
- Construct the design using exactly two 4-bit ripple counter instances.
- Drive the clock input of the second counter exclusively with the highest-order bit of the first counter.
- Do not route the external clock signal to the second counter stage.
Topics
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