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Making gain positive and NF less than 7.0 dB – I have designed a mm-wave amplifier, as I intend to add at least two more stages, the first stage being NF optimization and matching and the second for gain. The bias point of the amplifier is 4mA at Vds=1.2 and Vgs1=0.7v and Vgs2=1.0v with width of each transistor at 20 um such that we will get Jopt=0.2mA/μm on paper. To achieve above parameters, we will have to have vgs-vt=0.3 V and gm of 25.80 mS (W/L)=333.333 L=60 nm Now the MOSFET model used is BSIM4 with all default parameters except Vt0=0.4v (Don’t know how this will affect Vt as I don’t know how to calculate Vt ) What can be done to get positive gain and NF below 7dB? Read more
Transistor as a switch – I need to find a way that when Vin is “0” Vout will be 0V and when Vin is “1” Vout will 5V.
“1” -> 5V
“0” -> 0V
As you see, right now it is exactly the opposite of what I want. Do you have some idea how to do it without many changes? Read more
Non-contact current measurement – I am doing a project for non-contact current measurement using a Hall Effect sensor built into an air- gaped toroid core such as the Honeywell CSLA1CD ( +- 57A). My understanding is that the Hall Effect sensor is a transducer that outputs mV in relation to the flux density in a linear fashion. An idea I have come up with is to have a current carrying conductor pass through the toroid core, inducing a magnetic field onto the core, which will then concentrate the flux density onto the Hall Effect Sensor, which in return will output a mV value dependent upon the current passing through. I assume that this mV output is going to have to be amplified (I was thinking an LM358DT amplifier) before going into the ADC converter of a micro-controller (Arduino UNO) but my issue lies in the fact that I am not too sure what the gains of my amplifier should be or how to range the output/Arduino so that the displayed reading is accurate, or how to convert the signal going into the microcontroller from mV to mA to be read off of a LCD display. Read more
Automatic transfer switch design – This little circuit works perfectly in Proteus software for automatic transfer between AC mains line and inverter output. The design is straightforward. At its heart is an LM comparator or similar part that looks for 12 V DC derived from 220 AC mains. As long as it exists, the output will be zero and the transistors will never turn on. When the AC mains is missing, the 5 V DC from the regulator will be higher than the negative input comparator and the comparator output will swing to positive about 12 V. It works nicely but I am not aware of any real world surprises. Read more
Difference between PSD and spectrum measurement in Cadence – I am doing a transient analysis on a 3rd order SD modulator (MASH topology) and I want to plot the power spectrum of the quantization noise. I am confused on how to do that. My first try was sending the output sequence to Measurement tab—> Spectrum and ploting the curve. My second try was sending the output sequence to the calculator and using the psd() function, afterwards using db10() function and finally plotting. Could you enlighten me as to which is the correct way? Read more
Common mode feedback circuit – Can anyone tell me about the common mode feedback circuit (CMFB) which is required in a differential amplifier? Does this CMFB circuit only detect the DC voltage because the input of differential pair is Vin=Vcm+Vd where Vcm is the common mode DV voltage and Vd is the differential AC signal voltage? Read more
Discrete time integrator with transfer function – I am designing a discrete time integrator with transfer function = 1/(1-Z^-1) using a model writer of the Cadence virtuoso. Below is the VerilogA code of the integrator. But I am getting a gain of more than 1000 in the output, when applying an input signal of 900 uV (p-p). Read more
LM7912 regulator doesn’t work according to datasheet – I have a dual supply with the 7812 and 7912 regulators. I use the proper capacitors for filtering and stability. The power transformer’s (230V/2*24V with center tap) output is rectified by graetz-bridge. On the positive and the negative lines I use 20miliFarad/63V capacitors. The measured DC voltages are +34V and -34V. For the regulator ICs I shifted this voltage down with 2-2 8.2V/5W Zener diodes in series (reverse biased diodes). So at the INPUT pins the voltages are +18V and -18V (by the datasheet the max input voltages are +35V and -35V for the regulators). I measured an unused 7912 with labour supply. Under -20V the regulated output falls down. At -22V input voltage the output is -14V, at -27V input voltage the output is about -16V. Only between -14V and -20V the IC worked well, so I don’t understand what is the maximum -35V input voltage according to the datasheet. Read more
Non inverting amplifier using OPAmp LM358 – I constructed a non-inverting DC amplifier using 1/2 LM 358 with a gain of 10 employing the standard circuit. It does work at single supply of 5 V. Everything is fine if the output levels are less than approximately 3 V. The output never exceeds a certain value that ranges from 2.6 to 3 V irrespective of gain and input. I think this is the characteristic of the LM358 op amp — or there is something that is missing in my implementation? Read more
Help with mic preamp and AGC – I’d like to build a few mic preamps for my field recordings which usually involve low background noise and low sound levels. I can solder by following circuit drawings, however I am not able to design them. I thought I’d benefit from using a low noise high gain preamp with AGC and a switchable variable resistor to manually set gain those times I won’t need AGC. Here is a conceptual diagram I sketched (recorders would be portable battery powered ones, I currently have two, both with 3.5mm TRS jack mic input, 1 with 1.6 kΩ impedance and another with 2 kΩ impedance, unless I upgrade to something else). Read more.
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