ELEC5180: RF/Microwave Circuit Design and Measurement Course ...

Resistor: besides its resistance, parasitics include lead inductance
and contact capacitance.
An approximate equivalent circuit for a
resistor including parasitic elements
• For small resistors, the parasitic inductance dominates the parasitic
influence and will cause the impedance to rise at higher frequencies.
• For large resistors, parasitic capacitance dominates the parasitic
influence and will cause the impedance to drop at higher frequencies.
Problem at high frequencies:
- Increase of resistance due to Skin-Effect
- Inductive reactive component
- Capacitive reactive component
- Resonances (very high frequencies)
Ni/Cr, Tantalum Nitride (TaN),
doped semiconductors
Important features: stable resistance, lowtemperature
coefficients of resistance,
good heat dissipation capability,
maximum length of less than 0.1 λg, low
parasitics.
ELEC5180, Kevin Chen, HKUST 33
ELEC5180, Kevin Chen, HKUST 34
Capacitor: a dielectric sandwiched by two metal plates
C =
εA
d
Packaging and material properties are important
large packages and leads result in parasitic
inductance and can be modeled as an inductance in
series. Loss in the dielectric is modeled as a resistor
parallel to the capacitance.
Applications in circuits
- Determination of resonance frequency in oscillators and frequency filters
- RF-“short circuit“ (very small capacitive reactance)
- DC blocking
Some planar capacitor configurations
Self-resonance: generated by the capacitance, along with the
parasitic inductance, the resonance frequency may fall into your
measurement range. A typical SRF (self-resonance frequency) for a
10 pF high-Q ceramic capacitor is in the 2-4GHz range.
ELEC5180, Kevin Chen, HKUST 35
ELEC5180, Kevin Chen, HKUST 36