ECE 448: Lab 7 Design and Testing of an FIR Filter

Finite Impulse Response (FIR) Filters FIR: Given an impulse input, the filter output goes to zero in a finite number of clocks because there is no feedback of the output to the input Filter: manipulate the frequency response Examples: low-pass, high-pass, band pass, notch, arbitrary Equation: y: output x: input h: filter taps (coefficients) N: number of taps

Low Pass Filter

Parallel Architecture Output every clock cycle N multipliers (one per tap) One N-input adder N-stage shift register (no reset!) Constants h[i] stored in registers or hardwired Note the bit growth x[m] y[m] x[m-1] x[m-2] x[m-(N-1)]

Serial Architecture Output every N clock cycles One multiplier One 2-input adder N-stage shift register (no reset!) Constants h[i] stored in a single-port ROM Multiplier-Accumulator (MAC) Note the bit growth x[m] x[m-1] x[m-2] x[m-(N-1)] MAC h[i] y[m]

Parallel-Serial Architecture Output every N/K clock cycles K multipliers One K+1 input adder N-stage shift register (no reset!) Constants h[i] stored in N/K single-port ROMs Adder-Accumulator (AAC) Note the bit growth ROM with N/K coefficients... x[m] x[m-1] x[m-2] x[m-(N-1)] AAC y[m] N/K-to-1 MUX N/K-to-1 MUX.. ROM with N/K coefficients

Selected Architecture and Parameter Values Parallel-Serial Architecture N=256 K=16 L=M=18 Clock frequency = 100 MHz

Lab 4 Top Level Numerically Controlled Oscillator Finite Impulse Response Filter

Task 1: Numerically Controlled Oscillator (NCO) Number of samples per period = 1024/(4  step), where step = Distance between samples = 391 clock periods = 3910 ns Amplitude = 2 17 Generator of digital samples

Task 1: Numerically Controlled Oscillator (NCO) Calculates numerical samples of the sinusoidal signal f(t)=2 17  sin(2πt/1024) with the frequency determined by step=sw[5..0], which is in the range 0..63, and t is a value of an accumulator incremented by 4  step every 391 clock cycles Each sample is represented as an 18-bit signed integer in the range from to The total number of samples per period is given by 1024/(4  step) if step≠0, and 1 if step=0 The distance between samples is equal to 391 clock periods = 3910 ns Values of the function f(t)=2 17  sin(2πt/1024) for t= stored in Block RAM

Task 1: Numerically Controlled Oscillator (NCO) 6-bit Frequency Control Word (FCW) or step size 10-bit accumulator: sum[n] = sum[n-1] + step*4, sum[0]= bit signed sine values in a Lookup Table (LUT) Accumulator addresses the LUT Sine values stored in 1 Block RAM Update every 391 clock cycles valid pulse asserted for one clock cycle when output out updated

Task 1: Numerically Controlled Oscillator (NCO) Clock frequency of the oscillator: f OSC =  100 MHz = step  KHz ≈ step  1 KHz T OSC = 4  step 1024  391  T CLK 4  step 1024  391

Task 1: Simulating Analog Signals Change the signal property in ModelSim to: Show the waveform in analog form Change the height of the analog waveform Change the radix of the signal to signed or unsigned

Task 2: Filter 256-tap FIR Filter using Parallel-Serial Architecture K=16 18x18 Multipliers N=256 samples stored in a 256-stage shift register Taps stored in K=16 single-port ROMs of the size N/K x 18 = 16 x 18 Starts processing when valid input is high Generates a valid output pulse

Task 3: Magnitude, Scale, Moving Average Calculates when valid is high Magnitude: magnitude = abs(in) Scale: scale = magnitude / 2^28 Moving Average: Store 1024 of the most recent scaled values in circular buffer acting as a shift-register. Implement circular buffer using a 1024x16 Block RAM using CORE Generator sum[n] = sum[n-1] + scale[n] - scale[n-1024] Don’t forget to account for the accumulator bit growth avg = sum / 2^10

Task 3: Magnitude, Scale, Moving Average 0 Average Magnitude g(t)=abs(FIR(f(t)) FIR(f(t)) is an output from the filter Average Magnitude large if f(t) passed by the filter Average Magnitude small if f(t) attenuated by the filter

Task 4: Seven Segment Display

Task 5: Filter Select Switch[7:6] selects one of four filters in the Tap Buffer Sketch the frequency response of each filter

Task 5: Tap ROMs 64 deep

Task 6: Digital-to-Analog Converter Generates analog signal to show on oscilloscope Convert signed to biased unsigned (ex: [-128:127] to [0:255]) Button[0] cycles between the NCO, Filter, and Magnitude NCO selected: out = nco / 2^10and LED[0] on Filter selected: out = filter / 2^36and LED[1] on Magnitude selected: out = mag / 2^36and LED[2] on pmod[7..0] 8

8-Bit Parallel Digital-to-Analog Converter (DAC) PMOD-R2R

PMOD Pins on Board NET "PMOD "LOC = "T12"| IOSTANDARD = LVTTL ; NET "PMOD "LOC = "V12"| IOSTANDARD = LVTTL ; NET "PMOD "LOC = "N10"| IOSTANDARD = LVTTL ; NET "PMOD "LOC = "P11"| IOSTANDARD = LVTTL ; NET "PMOD "LOC = "M10"| IOSTANDARD = LVTTL ; NET "PMOD "LOC = "N9"| IOSTANDARD = LVTTL ; NET "PMOD "LOC = "U11"| IOSTANDARD = LVTTL ; NET "PMOD "LOC = "V11"| IOSTANDARD = LVTTL ;

Switch and Buttons Functions Switch[5:0] NCO Frequency Control Word (step) –Used in NCO and Shape Generator Switch[7:6] Filter Select Button[0] DAC Select –NCO –Filter –Magnitude

CORE Generator Demonstration