filter design (1)
DESCRIPTION
Filter Design (1). Jack Ou ES590. Outline. Butterworth LPF Design Example LPF to HPF Conversion LPF to BPF Conversion LPF to BRF Conversion. Butterworth Filter. (Attenuation of the Butterworth filter). Avoid ripples in the passband . - PowerPoint PPT PresentationTRANSCRIPT
Outline
• Butterworth LPF Design Example• LPF to HPF Conversion• LPF to BPF Conversion• LPF to BRF Conversion
Butterworth Filter
Avoid ripples in the passband.As n increases, the responses assumes a sharper transition.The 3dB bandwidth remains independent of n.
(Attenuation of the Butterworth filter)
Design Requirement for a Butterworth Low Pass Filter
The cut-off frequency is not known in this design specification.
Typical Bandpass Specifications
When a low-pass design is transformed into a bandpass design, the attenuation bandwidth ratios remain the same.
Transformation from LPF to BPF
• The Actual Transformation from LPF to BPF is accomplished by resonating each low-pass element with an element of the opposite type and of the same value. All shunt elements of the low-pass prototype circuit becomes parallel resonant circuits, and all series elements become series-resonant circuits.
Transformation Example
Resonate each low-pass element with an element of the opposite type and of the same value.
Design Example
f1=2472.5 MHzf2=2472.72f3=2494.28f4=2494.5 MHz (22)/(21.56)=1.0204
Center Freq: 2483.5 MHz
Design Example
f1=27 MHzf2=45 MHzf3=75 MHzf4=125 MHz
(98)/(45)=2.1778Thus fc/f=2
Center Freq: 58.1 MHz
Transformation from LPF
Replace each shunt element with a shunt series resonant circuit.Replace each series element with a series parallel resonant circuit.Both elements in each of the resonant circuits have the same normalized value.