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Signal Electromigration (Signal EM): Violations, Examples, and Practical Fixes

  Hello Dear Readers,   Today in this post, I will provide some deep insight into the Signal Electromigration (Signal EM): Violations, Examples, and Practical Fixes. 1. Introduction: As technology nodes shrink into the deep‑submicron and nanometer regime (7nm, 5nm, 3nm and beyond), electromigration (EM) has become a first‑order reliability concern—not only for power/ground (PG) networks but also for signal nets. Signal EM failures are often underestimated because signal currents are transient and bidirectional. However, with higher switching activity, tighter metal pitches, thinner wires, and aggressive timing closure, signal EM can cause latent or early‑life failures if not addressed properly. This article explains: What Signal EM is and how it differs from PG EM Typical Signal EM violation scenarios Detailed, practical examples Root causes behind each violation Proven solutions and best practices to fix and prevent Signal EM issues 2. What is Signal Electromigration: El...
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Modelling of Binary Encoding, Gray Encoding and One-hot encoding FSM using Verilog HDL

Hello Dear Readers, 

Today, I will explain how binary, gray, one-hot encoding FSM design using Verilog HDL.

1). Binary Encoding:

Binary encoding style can be used if the area requirement is a constraint on the design. In this encoding style state parameters for the binary encoding are represented in the binary format.

Two-Bit Binary Up-Counter FSM:

Two-bit binary counter FSM is described below, the number of states is equal to 4 and it needs four state variables ‘s0,’ ‘s1,’ ‘s2,’ and ‘s3.’ The number of flip-flops used to represent the functionality of the counter is equal to 2. The state transition table and the state transition diagram is shown in Fig.1 and Fig.2. The transition from one state to another state occurs on the positive edge of the clock. The default state is ‘s0’ and it is the reset state. So outcome is Moore machine as the output is a function of the current state only.

Fig.1 State Transition Table

Fig.2 State Diagram

Verilog Code:

module binary_count(clk,rst,y_out);

input clk,rst;

output reg [1:0]y_out;

parameter s0=2'b00,s1=2'b01,s2=2'b10,s3=2'b11;

reg [1:0]current_state,next_state;

// state logic definition

always @(posedge clk or negedge rst)

begin

  if(~rst)

     current_state<=s0;

  else

     current_state<=next_state;

end

// next state logic definition

always @(current_state)

case (current_state)

s0:next_state=s1;

s1:next_state=s2;

s2:next_state=s3;

s3:next_state=s0;        

default: next_state=s0;

endcase


//output logic definition

always @(current_state)

case(current_state)

s0:y_out=2'b00;

s1:y_out=2'b01;

s2:y_out=2'b10;

s3:y_out=2'b11;

default: y_out=2'b00;

endcase

endmodule

Simulational Results:

Fig.3 

2). Gray Encoding:

The Gray encoding style can be used if the area requirement is a constraint on the design. In this encoding style, state parameters are represented in the Gray format. 

Two-Bit Gray Counter FSM:

Two-bit Gray counter FSM is described below, the number of states is equal to 4 and it needs four state variables ‘s0,’ ‘s1,’ ‘s2,’ and ‘s3.’ The number of flip-flops used to represent the functionality of the counter is equal to 2. The state transition table and the state transition diagram is shown in Fig.4 and Fig.5. The transition from one state to another state occurs on the positive edge of the clock. The default state is ‘s0’ and it is the reset state. So the outcome is Moore machine as the output is a function of the current state only.

Fig.4 Gray Up-Counter State Table

Fig.5 State Diagram

Verilog Code:

module gray_count(clk,rst,y_out);

input clk,rst;

output reg [1:0]y_out;

parameter s0=2'b00,s1=2'b01,s2=2'b10,s3=2'b11;

reg [1:0]current_state,next_state;

// state logic definition

always @(posedge clk or negedge rst)

begin

  if(~rst)

     current_state<=s0;

  else

     current_state<=next_state;

end

// next state logic definition

always @(current_state)

case (current_state)

s0:next_state=s1;

s1:next_state=s3;

s3:next_state=s2;

s2:next_state=s0;        

default: next_state=s0;

endcase


//output logic definition

always @(current_state)

case(current_state)

s0:y_out=2'b00;

s1:y_out=2'b01;

s3:y_out=2'b11;

s2:y_out=2'b10;

default: y_out=2'b00;

endcase

endmodule

Simulational Results:

Fig.5 

3). One-Hot Encoding:
Two-bit Gray counter FSM is described below, the number of states is equal to 4 and it needs four state variables ‘s0,’ ‘s1,’ ‘s2,’ and ‘s3.’ The number of flip-flops used to represent the functionality of the counter is equal to 4. The state transition table is shown in Fig.6. The transition from one state to another state occurs on the positive edge of the clock. The default state is ‘s0’ and it is the reset state. So the outcome is Moore machine as the output is a function of the current state only.

Fig.6 State table for One-Hot Encoding FSM

Verilog Code:

module onehot_count(clk,rst,y_out);

input clk,rst;

output reg [1:0]y_out;

parameter s0=4'b0001,s1=4'b0010,s2=4'b0100,s3=4'b1000;

reg [3:0]current_state,next_state;

// state logic definition

always @(posedge clk or negedge rst)

begin

  if(~rst)

     current_state<=s0;

  else

     current_state<=next_state;

end

// next state logic definition

always @(current_state)

case (current_state)

s0:next_state=s1;

s1:next_state=s2;

s2:next_state=s3;

s3:next_state=s0;        

default: next_state=s0;

endcase


//output logic definition

always @(current_state)

case(current_state)

s0:y_out=2'b00;

s1:y_out=2'b01;

s3:y_out=2'b11;

s2:y_out=2'b10;

default: y_out=2'b00;

endcase

endmodule

Simulational Results:

Fig.7 






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Comments

  1. Anonymous17 September 2021 at 10:59

    Now clear doubts regarding modelling of one hot encoding FSM.

    ReplyDelete
  2. Anonymous17 September 2021 at 20:04

    perfectly as expected

    ReplyDelete
  3. Anonymous17 September 2021 at 20:29

    One of the favourite blog for the students who are doing mini projects.

    ReplyDelete
  4. Anonymous18 September 2021 at 21:45

    Such a fabulous work you are doing. Keep posting such kind of tutorial articles so we may be feel confidential on us.

    ReplyDelete
  5. Anonymous21 September 2021 at 02:03

    So now one hot FSM modelling doubts cleared thanks for this post.

    ReplyDelete
  6. Anonymous23 September 2021 at 06:40

    What a contents, in specifically VlSI field we never expect in free of cost this level of blogs thanks for your entire effort and I see inside you another Sandeep Maheshwari of VLSI field educator. Keep it up

    ReplyDelete
  7. ELECTRONICS AND COMMUNICATION HUBS8 September 2022 at 06:06

    Thanks for your words

    ReplyDelete

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