Analog Top Talks in July 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.

Problem measuring output impedance of CMOS inverter – Why am I getting negative output impedance using the following test circuit? Read more

Converting from 4 x AAA batteries to transformer or Li-ion batteries – I own an old calculator TI-84 SILVER EDITION powered by 4 x AAA 1,5 v batteries, I was wondering if it was possible to convert it to a pack of rechargeable smartphone batteries or connect it to a DC transformer. Read more

Minimum supply voltage – The schismatic as attached is class-ab, and it mentions the minimum supply voltage. What does that mean, and which transistor referring by
“The minimum supply voltage of the output stage equals two stacked gate-source voltages and one saturation voltage, which makes it suitable for low-voltage operation.” Read more

FM modulator using PLL working – In the attached FM modulator, what is the purpose of set deviation and deviation balance blocks? Why do they give the message signal to both TCXO and VCO? Where will I get more details about this circuit? Read more

Supply through series resistor problem – I have 5 volts coming out of an enclosure and entering another enclosure through a patch cable. The voltage needs to be current limited so that a user does not inadvertently short the supply as the patch cable and the various devices that can attach to it are designed to be plug and play and so it is quite possible that a user might plug something unexpected in, or do something to short the supply.  At times the 5v is simply across a potentiometer, with the wiper feeding back to the other enclosure, and for that application the limiting resistor is not a problem. However, the five volts is sometimes used to power an op-amp and uC circuit (about 40mA total) that don’t like working through the series resistor. Read more

Measuring sine wave accurately 500KHz – I have sourced a fixed 500KHz sine wave. It has a constant amplitude of 300mV PP. I want to make a circuit to monitor the amplitude precisely and to detect any change in the amplitude if occurred. The change might be in a few tens of microvolts. What is the best possible solution? Read more

Bias Tee configuration – I am designing an LNA to place right after an antenna to minimize the cable loss( also to deal with mixer products on later stages) induced into my receiver chain. I’m planning to place this LNA in a small-box right near the antenna for efficiency. Since starting this, I have seen a lot of Bias-tee conversation about it; but I’m confused about what is the difference between a Bias Tee and a normal RF choke. Read more

Constant current source – I have an NCP6354 and I want to use it as a constant current source to drive a 6w white led at 2000ma. How can I do it? Read more

How to define opamp specs within an active-RC filter – If we have to design an active-RC filter with some specs given, such as cut-off frequency, SFDR, and load, then how to define the opamp specs (GBW, slew rate, rin, rout)? It would be appreciated if any of you could provide some literature on this topic. Read more

No amplification observed when using THS3091 op amp – I replaced THS3095 IC on an Evaluation Board with THS3091. I am trying to run this op amp from a 24v power supply such that Vs+ is connected to 24v and Vs- to Gnd. as shown here. In my circuit, Rf=1k and Rg=110 ohm such that I can get 10 times amplification but it is not amplifying. Also, I have removed jp1, jp2, C9 and C10 Capacitors, which were being used in case of THS3095.