James J. Whalen

Computer-Aided Analysis of RFI Effects in Operational Amplifiers

The modified Ebers-Moll model is used to predict RFI effects in the 741 operational amplifier (op amp)-a bipolar linear integrated circuit (IC). RFI susceptibility predictions for RF incident upon the op-amp input terminals are made using a complete model, a macromodel, and a voltage-offset model. Both the batch-mode computer program SPICE 2 and the commercial interactive computer program ISPICE are used. The three sets of calculated results are essentially identical and agree within 4 dB with experimental results measured at 220 MHz. A threshold cannot be given for the RF power level at which a 741 op amp is susceptible to RFI. The level depends upon the op-amp circuit application. For op-amp circuits designed to amplify input signals in the 0.1-to 1.0-V range, RF power levels as large as -15 to + 5 dBm may be required to cause RHI susceptibility problems. For op-amp circuits designed to amplify input signals in the 1-to 10-mV range, RF power levels as low as -55 to -35 dBm may cause RHI susceptibility problems.

Rectangular waveguide shape folded patch antenna

A microstrip patch antenna is one of the most popular resonance antennas due to its light weight and easy fabrication and therefore widely used for many commercial electronic devices such as GPS receivers and for military applications such as airborne and aerospace communication [1]. A conventional patch antenna is constructed by two metallic layers which are separated by a thin dielectric layer. The upper metallic layer is responsible for radiation while the lower one works as the ground plane blocking electromagnetic (EM) waves propagating to the ground plane direction. Since the patch antenna shows good directivity in the broad side of the upper patch, electronic circuitry placed behind the ground plane would have little electromagnetic interference (EMI) from patch antenna radiation.

Electrically small tunable split ring resonator antenna

Since its physical implementation in 1999 by Pendry et al. [1], metamaterials which demonstrate negative permittivity and permeability have been raised as an interesting research topic in the microwave society for their unique features. Split ring resonator (SRR) is one of the most popular structures which could introduce negative permeability. Usually, a SRR is composed of two homocentric metallic rings, where each of them has a slot on the ring. The SRR works as an L-C resonance network whose resonance frequency can be determined by [2]

Electromagnetic interference in CMOS circuits

A model for predicting the radiofrequency interference (RFI) susceptibility of CMOS circuits at the design stage, using SPICE, is reported on. The circuit investigated is the RCA CD4007A, which contains three CMOS pairs of n-MOSFETs and p-MOSFETs, input protection circuits, output protection circuits, and parasitic pn-junctions, which behave as parasitic capacitors. The model was verified in both the presence and absence of RFI. The SPICE simulations correctly predict the frequency dependences of the RFI responses.<<ETX>>

Non-Bragg resonance in substrate integrated waveguide

Electromagnetic (EM) wave propagation in periodic structure is an interesting research topic in electronic, optical and laser systems. Conventionally, wave propagation in periodic media can be characterized by the Braggs law where the resonance frequency can be determined by the periodicity of the media and a wave incident angle. However, there is also a kind of non-Bragg resonance which cannot be characterized by the traditional Braggs law. A non-Bragg resonance has been observed in a rectangular waveguide with corrugated walls by the Cheng et al. [1]. The resonance frequency depends on the waveguide height (or thickness), the periods and amplitudes of the corrugations, and a phase shift between the corrugated walls. Since non-Bragg resonance only occurs under specific geometric conditions, it is also known as geometric resonance [1].

Parasitic capacitances can cause demodulation RFI to differ in inverting and noninverting operational amplifier circuits

The demodulation RFI responses of an inverting operational amplifier (op amp) circuit and a noninverting op amp circuit are compared. The intended voltage gain of the inverting op amp circuit is A/sub 1/=-R2/R1=-10. The intended linear voltage gain of the noninverting op amp circuit is A/sub N1/=(R1+R2)/R1=11. For both circuits, the resistor values are R1=10 k Omega and R2=100 k Omega . Analysis shows that parasitic capacitances C/sub in/ (between the inverting and noninverting inputs of the op amp) and CR1 (shunted across R1) cause the inverting op amp circuit to have better RFI immunity than the noninverting op amp circuit. The derivation is based on the hypothesis that the demodulation RFI response is caused by a second-order nonlinearity so that a 3-dB reduction in the linear voltage gain causes the second-order demodulation RFI response characterized by the transfer function H/sub 2/ to be reduced by 6 dB. For the assumed values of C/sub in/=8 pF and CR1=0.4 pF. the measured and calculated values of the difference between H/sub 2/ values for the inverting and noninverting circuits were in good agreement.<<ETX>>

The NARTE EMC credentials certification examination

The development and current status of questions for the NARTE EMC (electromagnetic compatibility) credentials Certification Exam are reviewed. The current question classification scheme which the author developed and how it has been used to prepare NARTE EMC exam No. 2 (summer and fall 1991) are discussed. The current status and future plans for EMC exam questions submitted by NARTE EMC engineers and technicians certified via the grandfather clause are also discussed.<<ETX>>

The Sensitivity of Demodulation RFI Predictions in Op Amp Circuits to Variations in Model Parameter Values

The computer program NCAP has been used to predict demodulation RFI effects in operational amplifier (op amp) circuits excited by 50% AM-modulated RF signals over the RF frequency range 0.1 to 400 MHz. The op amp circuit investigated is a unity gain buffer amplifier with 741 bipolar or LF355 JFET—bipolar op amps. The sensitivity of the RFI demodulation predictions to variations in model parameter values has been determined.

The NCAP Nonlinear T Model for Bipolar Junction Transistors at UHF Frequencies

The Nonlinear Circuit Analysis Program (NCAP) has been used to calculate nonlinear transfer functions which subsequently predict Electromagnetic Interference (EMI) effects in electronic circuits containing discrete semiconductor devices for RF frequencies up to 100 MHz. However, NCAP has not previously been tested nor documented in the UHF frequency range (300 to 3000 MHz). The purpose of this paper is to present the first predicted results of EMI effects in discrete bipolar junction transistors, using NCAPs nonlinear transfer functions, in the UHF range. The predicted results will be compared to experimental results.