Date: Wednesday, March 23 2022
Location: Pulse Hall 7 and 9
Time: 13:45 - 15:30
Power supply decoupling. This demonstration illustrates the occurrence of resonance peaks in power supply lines due to incorrect decoupling.
Download the SLiCAP archive supplyDecoupling.zip.
View the HTML output
Loop antenna measurements. In this demonstration we will perform measurements of which the results will be used to model the send and the receive coil of a hearing loop system.
Download the data sheet of the 100mH receive coil: RL622-104K-RC
This lecture (instruction) is to prepare for the practicum: March 25 2022, 13:45 - 15:30, Pulse Hall 7 and 9
Hearing loop systems are used for broadcasting audio information to individuals with T-Coil equipped hearing aids. They are used in public areas such as theatres, churches, meeting and conference rooms, etc.
The architecture of a hearing loop system is shown in the Fig 1.
Fig. 9 Architecture of a hearing loop system: A loop antenna converts the electrical audio signal into magnetic flux. A receive coil in the hearing aid converts this magnetic flux into a voltage. An amplifier in the hearing aid amplifies this voltage to drive the loudspeaker in the hearing aid.¶
The send and receive antennas will be provided. Behavioral models need to be based on measurement data, acquired during the demonstrations. Test and measurement equipment for characterization of the antennas is available in the Tellegen hal.
Maximum audio input level: 1V peak
Maximum audio output level with the receive coil placed in the center of the transmit coil: 0.25V peak
-3dB bandwidth: 60Hz … 15 kHz
Full-power bandwidth: 5kHz
Input impedance transmitter: > 10kOhm
Load impedance receiver: > 2kOhm
Receiver output noise (no input signal, frequency range 60Hz … 15 kHz) < 100uV RMS
Power supply voltage +/- 15V
Groups of four to six participants will design, build and test a hearing loop system. Two or three participants design and build the transmit coil driver, while the other two or three design and build the receive coil amplifier. All group members participate in the selection of the system architecture (amplifier types) and in the the definition and the execution of the test plan.
The design comprises the following steps:
Design a lumped element network model of the transmit coil
Design a lumped element network model of the receive coil
Set-up selection criteria for the electrical quantity driving the transmit coil and for the electrical quantity to represent the information from the receive coil
Design the system architecture, model the transfer, and derive specifications for the amplifiers:
type and gain
noise requirements
signal levels and drive capability requirements
frequency response
Design a test plan
Design the transmit coil driver amplifier
Design the receive coil amplifier
Build the system
Execute the test plan
Discuss the results with each other and with the instructors
Data sheet 100mH receive coil: RL622-104K-RC
Data sheet proposed operational amplifier TL081C
Data sheet high current driver BUF634
Give biasing design considerations for the antenna amplifier.
The figure below shows a feedback biasing scheme for the active antenna. The biasing resistor \(R_B\) provides a feedback path that makes the DC output voltage of the controller equal to the DC voltage at the non-inverting input of the controller (OpAmp).
The input offset voltage of the controller as well as its input bias current cause deviations of the DC output value of the OpAmp from its ideal value.
The noise contribution of the bias resistor \(R_B\) should be low enough to satisfy the requirements.
The resistance of \(R_B\) should be such that it does not change the frequency response of the active antenna over the frequency range of interest.
Output AC coupling with \(C_c\) is used to make the DC voltage at the cable independent of the DC output voltage of the OpAmp.
You may assume a 9V DC power supply
The design task is to discuss requirements and determine show-stopper values for:
The value of \(R_B\)
The value of \(C_c\)
The DC output voltage of the OpAmp
The DC bias current of the OpAmp
The output voltage and current drive capability of the OpAmp
The common-mode input voltage range of the OpAmp
The results should be presented in a SLiCAP HTML report (Zipped html sub directory of your SLiCAP project).
