From cf3373a4744b8350ddde613bc6813e2556bd6892 Mon Sep 17 00:00:00 2001 From: Denis Chevalier Date: Sun, 9 Aug 2026 00:29:10 +0200 Subject: update where it enters for resistor thermal noise --- module-design.typ | 16 +++++++++++++--- 1 file changed, 13 insertions(+), 3 deletions(-) (limited to 'module-design.typ') diff --git a/module-design.typ b/module-design.typ index 4d8c142..d3cca58 100644 --- a/module-design.typ +++ b/module-design.typ @@ -1217,9 +1217,19 @@ $ ====== Where it enters -- Input resistors in summing amplifiers, -- Feedback resistors (noise is gained at output), -- High-impedance nodes (input buffers, integrators). +/ Front-panel input nodes: The mandated $Z_"in" gt.eq qty(1, "mega ohm")$ + impedance om white input jacks creates an unavoidable + $approx qty(18.2, "uVrms")$ noise floor right at the module boundary. This + necessitates dropping internal suming nodes down to $qty(1, "kilo ohm")$ + post-buffering to prevent additive thermal noise accumulation, +/ Feedback resistors: Thermal noise generated in feedback elements is scaled to + the output by the stage's noise gain ($G_N = 1 + R_f / R_"in"$). + Consequently, even attenuating configurations ($R_f lt R_"in"$) maintain + $G_N gt.eq 1$, meaning thermal noise is never attenuated along with the + signal, +/ Input resistors: In summing junction amplifiers, +/ High-impedance nodes: Within integrators, sample-an-holds, and + current-to-voltage converters. ====== Scaling law -- cgit