Analog Top Talks in November on EDABoard.com forums

Peer-to-peer, engineer-to-engineer questions and answers from the EDABoard.com engineering community around analog ICs and analog design. Click the “Read more” link and follow the entire conversation and maybe add your two cents by logging in to EDAboard.com.

24V control from 3.3V – I am trying to drive a load of 24V and control that line by using a P MOSFET (U1). At gate of U1 I have an NMOS (2N7002) that control the gate signal. Read more

How can I eliminate this spike-like noise? – As a part of a big system Arduino is being effected from a switch outside(so the spike is not always there only when an outside switch or surge happens ect.) and I guess through its USB producing spikes on its output. How can I eliminate this spike? Read more

Achieving minimum load current for SSR for weak loads – For an enclosure, I will control the power at the terminals of a panel mount AC socket by using an SSR. The AC mains socket will have this indicator lamp in parallel to indicate whether the socket is live/powered. So my questions are:

1-) Is my RC values fine for this application? Is it fine to use a 480V AC rated capacitor with a 100 Ohm 10W resistor in my case? What type of capacitor and resistor recommended?

2-) In this forum there are warnings about usinga capacitor for zero crossing SSRs. Does anybody have experience with that? Read more

C-band SATCOM question – I’m reading the article “Satellite Basics” at http://www.idirect.net/Company/Resou…e%20Basics.pdf. The following can be read for C band: “Because of its weaker power it requires a larger antenna …” Question: why weaker power? Does it relate to C band? Read more

Circuit suggestion current limited power supply – I need to make a 5V 20mA current limited for use with 10kOhm and 20kOhm potentiometer-type devices. Because of the potentiometer low resistance at the ends of its ends, if I use an unlimited power supply, and even I set it as low as a few volts, it can destroy the pot due to heating of the element. Read more

Amplifier output with capacitive loading – I am designing a most basic amplifier: NMOS differential input, pMOS current mirror loading. The output terminal is only planning to drive a cap. My simulation output is in the picture below. The red is the output without a cap and the green is with a cap. We can see the green curve is way less ideal compare to red. My analysis is as follow…Read more

How to define port in Cadence – I am trying to use a port with complex value as an output termination in SP simulation of Cadence. For example, output port impedance value is 1/(2*pi*freq*C) which is also frequency dependent. Is there any idea how to do this in Cadence? Read more

Current clamp oscillating at 50Mhz – We have a DALI power bus comprising a 15mA current clamp in a 15V rail. (as in attached schematic). As a test, I turned on the transistor, Q4. When I clipped a TA041 differential probe across the 82R resistor, I saw a 50MHz sinusoidal oscillation across this resistor, of about 250mV pk2pk. (I was using a 50MHz scope). The current in the 82R was on average less than 15mA — about 11mA on average. Read more

Bidirectional HF amplifier  – Here is the diagram of an HF preamplifier. The single direction version at the left consumes about 30mA (biased in class-A for less distortion. Two questions:
1. Will the hard biased left version mean in general a higher dynamic range apart from low distortion?
2. Will the bidirectional right version work? Note only one of the two transistors will be switched for each direction and the other will stay off (not feeding any DC to its collector). Even if only one section will be on, I am still worried about interactions between the two stages. Read more

Very thin RF trace – My PCB thickness is very thin, and my PCB supplier gives me the calculation of a microstrip impedance line for 50Ω, which results in a trace width of 75µm, trace length about 20mm. The trace is connecting the output of RFIC PA to BAW filter and the application will use Bluetooth Low Energy. Will this very thin 75µm trace be a problem to handle the power transmitted by Bluetooth Low Energy for worst case scenario? Read more