Analog Top Talks in June 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.

Output impedance of asymmetric differential pair – Do you guys have any idea how to select MOSFET sizing of an asymmetric differential pair for maximum output impedance? I have derived the Rout expression here. Read more

Loop-gain calculation – I think this pic belongs to Allen CMOS analog circuit design book. I found it in an internet file. I want to know how can I calculate loop-gain in this pic. Read more

I need a simple water level indicator – I need a water level alarm circuit to use in the radiator tank of my car. I want the alarm to go ON when the water level is in the middle and I prefer a discontinuous beeps sound as an indicator. Read more

DC current pulse sensing – I want to design a circuit that senses a change in current flowing through a variable load. The current is DC and the load draws anywhere between 90mA to 300mA nominal. During a fault condition, the load the load current dips (reduces) briefly for around 200us by 20mA and then goes back to 300mA. This means that, for let’s say 300mA load current, the current goes to 280mA for around 200us and returns back to 300mA. The common voltage is 48VDC. I am planning to use a current sense amplifier like TI’s INA301 or similar to sense the current but I don’t want to use an ADC to detect the current dip. I want to use a comparator so that I can just get a ‘1’ or ‘0’ when the current dips 20mA. Any ideas or hints of how I can achieve this? Read more

Why does this current limiter oscillate? – I’m struggling to figure out why the circuit below oscillates at about 2-300khz. Changing the value of C10 seems to have no effect, neither does adding an output gate resistor, or adding an input resistor to the non-inverting input. Read more

Audio amplifier ever in class B – My class AB amp remains in class B. Here is the schematic:

What is the oscilloscope out: (simulated because I don’t have a photo)

In the simulation it is perfect. Read more

BLDC blower motor producing more noise – I’m running blower for a 3-phase BLDC motor with hall effect sensor feedback using the IR2110 driver. Motor producing more noise which is affecting other digital circuits. Read more

OTA along with class AB output stage – I need help in designing an op amp consisting of OTA and class AB output stage. I have come up with circuit in the attachment. Can anyone show me how to go about designing from the second stage? Read more