14
votes
How does an emitter follower work as an AM detector?
With no input signal, the bias network sets the base voltage to be about 3.4V. The emitter voltage is set to around 2.8V (depending on temperature) from a small amount of current coming from the ...
- 442
14
votes
Accepted
How are RF filters constructed?
As you've discovered, once you are up in the 100MHz+ range, little is "simple".
When using discrete capacitors and inductors, you have to consider their parasitic complements. Even basic ...
- 6,206
9
votes
How can I calculate the total impedance of a second-order low-pass filter?
I have looked at this quickly, applying the fast analytical techniques or FACTs as described in my book on the subject. You first start by determining the input resistance for \$s=0\$: open the cap ...
- 21.1k
9
votes
Accepted
How can I clip a voltage upper limit in an analog signal?
Many ICs have input protection diodes that will become conductive when the input falls outside the bounds of the power supply potentials (one or the other diode becomes forward biased), having a ...
- 28.9k
9
votes
Accepted
Trouble with filter using Laplace transfer function in LTSpice
Save some grief: set \$\omega=1\$
Just save yourself some algebra grief and set \$\omega=1\$ when focused on a particular filter shape (like Bessel.) The filter shape can be moved around freely (at ...
- 5,682
8
votes
Accepted
USB 2.0 VBUS Filter
Letters and Decimal Points
What does 5V0 mean? I've seen this net name used in other USB circuit diagrams (figure 1 here for example). Is 5V0 a convention used to indicate something different from ...
- 6,409
8
votes
What is the purpose of the resistor in a RC circuit?
simulate this circuit – Schematic created using CircuitLab
Figure 1. (a) All pass. (b) High pass.
I understand that a capacitor can pass high frequencies and block low frequencies, because of ...
- 171k
7
votes
How can I clip a voltage upper limit in an analog signal?
Usually, when a very low level ANALOG input signal is to expected, a resistor is placed in series with the input, with a diode in parallel, like this:
simulate this circuit – Schematic created ...
- 5,401
7
votes
How does an emitter follower work as an AM detector?
You are correct that if the emitter follower were employed as a linear element, it would be unable to perform AM demodulation. However, it is not as linear as you think.
This NPN emitter follower has ...
- 28.9k
7
votes
How to find the Transfer Function of this circuit?
You can easily determine the transfer function of this circuit by considering a simple \$RC\$ low-pass filter followed by a non-inverting structure described in this Wikipedia link. Because the op-amp ...
- 21.1k
7
votes
Opamp Non inverting Input
Although an ideal op-amp will have zero input currents, a real op-amp will always have some current, called the input bias current on data sheets. For CMOS and other FET amplifiers, it can be very ...
- 162k
7
votes
Input filter LC for switching power supplies
That's probably fine.
A complete analysis requires much more information (voltage range, amount of ripple and noise, surge conditions if applicable, environmental, etc.), but these data likely don't ...
- 27.4k
6
votes
Accepted
Input filter transfer function derivation
If you want to derive the transfer function linking the current signature of the buck converter to the current going to the battery, you don't need to include the battery voltage in the calculation:
...
- 21.1k
6
votes
Accepted
Input filter to reduce conducted emissions caused by DC/DC converter
Everything starts with the current signature of the dc-dc converter fed by the EMI filter. For instance, you simulate your converter at steady-state and extract the input current. If the EMI filter is ...
- 21.1k
6
votes
Accepted
Simulating a tuning circuit in LTspice
You have made a low Q or wideband filter. Increase R1 to sharpen it up. Try 10K then 100K.
- 14.3k
6
votes
Simulating a tuning circuit in LTspice
Well, let's analyze this circuit. The transfer function is given by:
\begin{equation}
\begin{split}
\mathscr{H}\left(\text{s}\right)&=\frac{\text{V}_\text{o}\left(\text{s}\right)}{\text{V}_\text{i}...
- 7,378
6
votes
How does an emitter follower work as an AM detector?
AM modulation is basically to multiply the carrier (C) and message (M) signals. And the result is, simply, the carrier signal "enframed" by the message signal:
Above shows a 1 kHz signal (...
- 30.3k
6
votes
Accepted
How to improve the performance of my low pass filter design
The LMH6626 is not unity gain stable!
- 3,173
5
votes
How to reduce oscillations in this active filter circuit?
Sallen-Key is the topology, Gaussian is the name of the filter design. Just to be clear, Gaussian filters are non-causal by design, which is why the filters that you'll meet in the wild are ...
- 21.2k
5
votes
RLC band-pass filter
Your simulation is only running between 100 KHz and 10 MHz.
Try editing the command to:
.ac dec 1000 10 100K
- 3,411
5
votes
Accepted
Ripple rejection of capacitance multiplier when compared to linear regulators
1 - Why the Capacitance Multiplier has a better response ‘filtering’
the higher frequencies
The very low quiescent current of the MCP1700 suggests that \$gain \times bandwidth\$ product is not ...
- 24.4k
5
votes
Simulating a tuning circuit in LTspice
As pointed out by @Autistic, your filter is too "broad" ...
- 12k
5
votes
Accepted
unfamiliar notch filter configuration
This is one of those interesting circuits.
The upper amplfier, U1, is a differential amplifier. When redrawn, as below, the differential amplifier topology becomes clear.
The Lower amplfier, U2, is a ...
- 8,489
5
votes
General formula for the ripple voltage in a loaded bridge rectifier
What is the general formula to calculate the peak to peak ripple voltage and Vdc average of the voltage at the input of the 7805 voltage regulator in a circuit like this?
The general formula should ...
5
votes
Accepted
strange phase behavior RC low pass filter
Electrolytic capacitors have fairly large ESR values, and they're fairly constant across frequency. As the reactive impedance drops according to frequency, the total impedance becomes dominated by ...
4
votes
Elliptic filter - implementation deviates from the design and simulation
However, after around 30 MHz the attenuation gradually reduced and stayed almost constant
This measurement indicates that the inductors are likely beyond self-resonance. It results in a cascade of ...
- 13.6k
Only top scored, non community-wiki answers of a minimum length are eligible