From 07ee771a96263eeaa3501362038bde5632f03bde Mon Sep 17 00:00:00 2001
From: rlar <rlar>
Date: Tue, 3 Mar 2015 21:27:29 +0100
Subject: [PATCH] noise analysis, bug fix, override ac magnitude of all
 vsrc/isrc devices

Bug report due to Hartmut Henkel in
>> [Ngspice-users] Noise analysis depends on ac parameter

The noise analysis internally depends on an ac analysis
  to derive "inoise" from "onoise"
("onoise" is multiplied with the inverse ac gain from input to output)

This AC analysis used all the given ac magnitudes for all vsrc/isrc
  devices in the deck.

This fix overrides all ac magnitudes with zero,
  except for the given input device,
  whose magnitude is set to one.
---
 src/include/ngspice/cktdefs.h        |  5 +++++
 src/spicelib/analysis/noisean.c      |  5 +++--
 src/spicelib/devices/isrc/isrcacld.c | 18 ++++++++++++++----
 src/spicelib/devices/vsrc/vsrcacld.c | 14 ++++++++++++--
 4 files changed, 34 insertions(+), 8 deletions(-)

diff --git a/src/include/ngspice/cktdefs.h b/src/include/ngspice/cktdefs.h
index f129016a9..451b4dc51 100644
--- a/src/include/ngspice/cktdefs.h
+++ b/src/include/ngspice/cktdefs.h
@@ -165,6 +165,9 @@ struct CKTcircuit {
 #define MODETRAN           0x1
 #define MODEAC             0x2
 
+/* for noise analysis */
+#define MODEACNOISE        0x8
+
 /* old 'modedc' parameters */
 #define MODEDC            0x70
 #define MODEDCOP          0x10
@@ -288,6 +291,8 @@ struct CKTcircuit {
 
     NGHASHPTR DEVnameHash;
     NGHASHPTR MODnameHash;
+
+    GENinstance *noise_input;   /* identify the input vsrc/isrc during noise analysis */
 };
 
 
diff --git a/src/spicelib/analysis/noisean.c b/src/spicelib/analysis/noisean.c
index 48345d9a3..340184b02 100644
--- a/src/spicelib/analysis/noisean.c
+++ b/src/spicelib/analysis/noisean.c
@@ -37,13 +37,13 @@ NOISEan (CKTcircuit *ckt, int restart)
     double freqTol; /* tolerence parameter for finding final frequency; hack */
 
     NOISEAN *job = (NOISEAN *) ckt->CKTcurJob;
+    GENinstance *inst = CKTfndDev(ckt, job->input);
 
     posOutNode = (job->output) -> number;
     negOutNode = (job->outputRef) -> number;
 
     /* see if the source specified is AC */
     {
-        GENinstance *inst = CKTfndDev(ckt, job->input);
         bool ac_given = FALSE;
 
         if (!inst || inst->GENmodPtr->GENmodType < 0) {
@@ -194,7 +194,8 @@ NOISEan (CKTcircuit *ckt, int restart)
 	    return (E_PAUSE);
         }
 	ckt->CKTomega = 2.0 * M_PI * data->freq;
-	ckt->CKTmode = (ckt->CKTmode & MODEUIC) | MODEAC;
+	ckt->CKTmode = (ckt->CKTmode & MODEUIC) | MODEAC | MODEACNOISE;
+	ckt->noise_input = inst;
 
 	/*
 	 * solve the original AC system to get the transfer
diff --git a/src/spicelib/devices/isrc/isrcacld.c b/src/spicelib/devices/isrc/isrcacld.c
index 5ddbec373..2a8cefff1 100644
--- a/src/spicelib/devices/isrc/isrcacld.c
+++ b/src/spicelib/devices/isrc/isrcacld.c
@@ -23,16 +23,26 @@ ISRCacLoad(GENmodel *inModel, CKTcircuit *ckt)
         for (here = model->ISRCinstances; here != NULL ;
                 here=here->ISRCnextInstance) {
 
+            double acReal, acImag;
+
+            if ((ckt->CKTmode & MODEACNOISE) && (here == ckt->noise_input)) {
+                acReal = 1.0;
+                acImag = 0.0;
+            } else {
+                acReal = here->ISRCacReal;
+                acImag = here->ISRCacImag;
+            }
+
             m = here->ISRCmValue;
 
             *(ckt->CKTrhs + (here->ISRCposNode)) +=
-                m * here->ISRCacReal;
+                m * acReal;
             *(ckt->CKTrhs + (here->ISRCnegNode)) -=
-                m * here->ISRCacReal;
+                m * acReal;
             *(ckt->CKTirhs + (here->ISRCposNode)) +=
-                m * here->ISRCacImag;
+                m * acImag;
             *(ckt->CKTirhs + (here->ISRCnegNode)) -=
-                m * here->ISRCacImag;
+                m * acImag;
         }
     }
 
diff --git a/src/spicelib/devices/vsrc/vsrcacld.c b/src/spicelib/devices/vsrc/vsrcacld.c
index 5b7b9058b..8229bb842 100644
--- a/src/spicelib/devices/vsrc/vsrcacld.c
+++ b/src/spicelib/devices/vsrc/vsrcacld.c
@@ -22,12 +22,22 @@ VSRCacLoad(GENmodel *inModel, CKTcircuit *ckt)
         for (here = model->VSRCinstances; here != NULL ;
                 here=here->VSRCnextInstance) {
 
+            double acReal, acImag;
+
+            if ((ckt->CKTmode & MODEACNOISE) && (here == ckt->noise_input)) {
+                acReal = 1.0;
+                acImag = 0.0;
+            } else {
+                acReal = here->VSRCacReal;
+                acImag = here->VSRCacImag;
+            }
+
             *(here->VSRCposIbrptr) += 1.0 ;
             *(here->VSRCnegIbrptr) -= 1.0 ;
             *(here->VSRCibrPosptr) += 1.0 ;
             *(here->VSRCibrNegptr) -= 1.0 ;
-            *(ckt->CKTrhs + (here->VSRCbranch)) += here->VSRCacReal;
-            *(ckt->CKTirhs + (here->VSRCbranch)) += here->VSRCacImag;
+            *(ckt->CKTrhs + (here->VSRCbranch)) += acReal;
+            *(ckt->CKTirhs + (here->VSRCbranch)) += acImag;
         }
     }