Summing junction
A summing junction adds two signals, each with a gain of its own. A gain of −1 on one input subtracts it: an error signal from a measurement and a set point, or a balanced pair.
Ports
Two inputs, a and b, and one output, out.
The model
\[v_\text{out} = g_a v_a + g_b v_b,\]for the DC and for each tone, tones at one frequency adding as complex amplitudes. The noise adds as powers:
\[S_\text{out}(f) = g_a^2 S_a(f) + g_b^2 S_b(f),\]the two taken as unrelated, even when they come from one source by two paths. Two inputs of one unit (both volts, or both amps) keep it; otherwise the output is in volts.
Settings
| Field | Default | Meaning |
|---|---|---|
ga | 1 | Gain, a |
gb | 1 | Gain, b |
From the tool's own tables, file format version 1: the names are those in a .jekray file.
Readouts
The panel gives its output in the steady state: the DC level, the five strongest tones (each one’s amplitude, rms and the phase of its cosine), and the noise, as a density at 1 kHz and in rms from 1 Hz to 1 GHz. Any notes, such as an input left unwired, are listed under it.
Assumptions
- Ideal and noiseless, at every frequency.
- Noise reaching both inputs from one source adds as powers, not as fields: correlated noise does not cancel when subtracted.