B sources (common examples) - Revision history

Analogspiceman: /* Building other functions with b-sources */ removed dup

2019-11-01T17:11:33Z

‎Building other functions with b-sources: removed dup

Analogspiceman: Added second example category

2019-11-01T17:09:16Z

Added second example category

Analogspiceman at 17:34, 31 October 2019

2019-10-31T17:34:50Z

Analogspiceman: /* * Replicating the MODULATOR a-device */

2019-10-30T17:29:47Z

‎* Replicating the MODULATOR a-device

Analogspiceman at 06:31, 29 October 2019

2019-10-29T06:31:37Z

Analogspiceman: /* Up/Down Counter in a single b-source */

2019-10-29T06:31:08Z

‎Up/Down Counter in a single b-source

Analogspiceman: /* * Other, Notes, etc. */

2019-10-29T06:30:45Z

‎* Other, Notes, etc.

Analogspiceman: /* * State Machine Helper Logic */

2019-10-29T06:09:30Z

‎* State Machine Helper Logic

Analogspiceman at 03:05, 29 October 2019

2019-10-29T03:05:03Z

Analogspiceman: /* D Flip-Flop (with Q-not feedback to create divide by two counter) */

2019-10-29T02:43:36Z

‎D Flip-Flop (with Q-not feedback to create divide by two counter)

← Older revision		Revision as of 17:11, 1 November 2019
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	=== Building other functions with b-sources ===		=== Building other functions with b-sources ===
−
−	~~==== * Edge triggered b-source logic and integrated averaging in LTspice ====~~
−
−	These following functions are intended to be used in b-sources. The first two replicate edge triggered logic such as is used in the a-device DFLOP clock input. The last function is more complicated as it includes three behavioral integrators to provide a running integrated average of x (starting on the falling edge of sampling pulse s) that is then held until the next rising edge of sampling pulse s. In normal use, x would be an analog input and the sampling pulse s would be a series of very narrow 1 volt positive digital pulse.
−
−	~~.func up(s) buf( ddt(s)) ; generates pulse on rising edge of s~~
−	~~.func dn(s) buf(-ddt(s)) ; generates pulse on falling edge of s~~
−
−	* The following averages x between sample pulses s
−	~~.func ave(x,s) sdt(0,sdt(x,0,dn(s))/sdt(1,0,dn(s)),up(s))~~
−
−	~~B1 0 1 I= ave(V(x),V(s)) Rpar=1 Cpar=1n ; source for x and s not shown~~

	==== * State Machine Helper Logic ====		==== * State Machine Helper Logic ====

@@ Line 88: / Line 88: @@
   B1 0 sinB I=sin(wo*sdt(V(f))) Rpar=1 Cpar=1µ
   B2 0 cosB I=cos(wo*sdt(V(f))) Rpar=1 Cpar=1µ
 ==== * State Machine Helper Logic ====

← Older revision		Revision as of 17:34, 31 October 2019
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−	~~Add examples such as:~~	+	For a listing of all b-source functions see [[B sources (complete reference)]].

	=== When, why and how to use ''tripdt'' and ''tripdv'' with explanation ===		=== When, why and how to use ''tripdt'' and ''tripdv'' with explanation ===

@@ Line 83: / Line 83: @@
   A1 f 0 0 0 0 cosA sinA 0 MODULATOR Mark={fo} Space=0
-The b-sources below produce the same swept waveforms on V(sinB) and V(cosB).  R1 and R2 are not really necessary except to duplicate the output impedance of the a-device, however C1 and C2 are important for waveform fidelity.  They are needed to "trick" LTspice into producing enough waveform data points as the frequency increases.  (Because b-sources are general purpose devices, it is often a problem to get them to correctly control step size.)
+The b-sources below produce the same swept waveforms on V(sinB) and V(cosB).  R1 and R2 duplicate the output impedance of the a-device and C1 and C2 are important for waveform fidelity and must be selected based on the frequency range of interest.  They are needed to "trick" LTspice into producing enough waveform data points as the frequency increases.  (Because b-sources are general purpose devices, it is often a problem to get them to correctly control step size.)
   .param wo=2*Pi*fo
-  B1 s 0 V=sin(wo*sdt(V(f)))
+  B1 0 sinB I=sin(wo*sdt(V(f))) Rpar=1 Cpar=1µ
-  B2 c 0 V=cos(wo*sdt(V(f)))
+  B2 0 cosB I=cos(wo*sdt(V(f))) Rpar=1 Cpar=1µ
 ==== * State Machine Helper Logic ====

← Older revision		Revision as of 06:31, 29 October 2019
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	Another useful function might be to add a parameter called something like “StateChange” that would go high only during state transitions and be low otherwise. Note that this incorporated in the b-source function above as buf(abs(ddt(V(state)))).		Another useful function might be to add a parameter called something like “StateChange” that would go high only during state transitions and be low otherwise. Note that this incorporated in the b-source function above as buf(abs(ddt(V(state)))).
−

	==== * Up/Down Counter in a single b-source ====		==== * Up/Down Counter in a single b-source ====

← Older revision		Revision as of 06:31, 29 October 2019
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−	==== Up/Down Counter in a single b-source ====	+	==== * Up/Down Counter in a single b-source ====

	B1 0 cnt I=sdt(0, round(V(cnt)+buf(ddt(V(up)))-buf(ddt(V(dn)))), buf(ddt(V(up)+V(dn))) ) Rpar=1 Cpar=10n		B1 0 cnt I=sdt(0, round(V(cnt)+buf(ddt(V(up)))-buf(ddt(V(dn)))), buf(ddt(V(up)+V(dn))) ) Rpar=1 Cpar=10n

← Older revision		Revision as of 06:30, 29 October 2019
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	Another useful function might be to add a parameter called something like “StateChange” that would go high only during state transitions and be low otherwise. Note that this incorporated in the b-source function above as buf(abs(ddt(V(state)))).		Another useful function might be to add a parameter called something like “StateChange” that would go high only during state transitions and be low otherwise. Note that this incorporated in the b-source function above as buf(abs(ddt(V(state)))).
		+
		+
		+	==== Up/Down Counter in a single b-source ====
		+
		+	B1 0 cnt I=sdt(0, round(V(cnt)+buf(ddt(V(up)))-buf(ddt(V(dn)))), buf(ddt(V(up)+V(dn))) ) Rpar=1 Cpar=10n
		+
		+	The b-source is a current source Nortonized into voltage source with a 1 ohm output impedance. The b-source parallel capacitor must be 2x the slowest rise time of the up/down inputs. In between up and down count pulses the sdt function holds the last count.
		+
		+	The up and down inputs, V(up) V(dn), use LTspice's standard 1 volt logic levels and trigger on the positive edges.
		+
		+	The cnt (count) output is an integer count that starts from zero. I haven't shown a reset, but it would be very easy to add.

	==== * Other, Notes, etc. ====		==== * Other, Notes, etc. ====

@@ Line 101: / Line 101: @@
 Another useful function might be to add a parameter called something like “StateChange” that would go high only during state transitions and be low otherwise.  Note that this incorporated in the b-source function above as buf(abs(ddt(V(state)))).
-----
+==== * Other, Notes, etc. ====
 ''I've got an equation in an arbitrary behavioral source that uses the variable *TIME* to plot.&nbsp; What I can't figure out is how to cause this to repeat at some interval.''
@@ Line 128: / Line 120: @@
 Now, within your b-source equation, you could replace each instance of "time" with either "a(r)" or "b(r)" (or change the names to suit what makes sense to you).
 {{#widget:DISQUS

@@ Line 50: / Line 50: @@
 Building an edge triggered digital device also requires a similar indirect application of the Verilog differentiation function, ddt(x).  To detect the positive going edge of an input clock pulse stream, it must first be squared up (ideally buffered to a logical one or zero), then differentiated and buffered again to produce a pulse only on the positive edge.  Here is the SPICE code:
-==== 1. Edge triggered b-source logic and integrated averaging in LTspice ====
+==== * Edge triggered b-source logic and integrated averaging in LTspice ====
 These following functions are intended to be used in b-sources.  The first two replicate edge triggered logic such as is used in the a-device DFLOP clock input.  The last function is more complicated as it includes three behavioral integrators to provide a running integrated average of x (starting on the falling edge of sampling pulse s) that is then held until the next rising edge of sampling pulse s.  In normal use, x would be an analog input and the sampling pulse s would be a series of very narrow 1 volt positive digital pulse.
@@ Line 62: / Line 62: @@
   B1 0 1 I= ave(V(x),V(s)) Rpar=1 Cpar=1n ; source for x and s not shown
-==== 2. D Flip-Flop (with Q-not feedback to create divide by two counter) ====
+==== * D Flip-Flop (with Q-not feedback to create divide by two counter) ====
   * Divide by two counter (D flip-flop with Q-not data feedback)
@@ Line 75: / Line 75: @@
 Because they are general purpose devices, b-sources are computationally burdened with carrying a full Jacobian (although this can be turned off - often with disastrous results - with the NoJacob parameter).  Also, since b-sources are largely analog devices, they do not have a built-in provision to recognize state changes like the digital a-devices do (yes, this can be less effectively approximated with b-sources by specifying the tripdv and tripdt parameters).  The bottom line is that in LTspice it is always better to use a-devices whenever they fit the requirement.
-==== 3. Replicating the MODULATOR a-device ====
+==== * Replicating the MODULATOR a-device ====
 In the netlist below a MODULATOR a-device is set up with 1V=100Hz and 0V=0Hz.  It is then driven by V1 to sweep from 50Hz to 150Hz over 1 second.  The frequency control input is V(f) and its swept outputs are V(sinA) and V(cosA).
@@ Line 93: / Line 93: @@
   R2 cosB c 1
-==== 4. State Machine Helper Logic ====
+==== * State Machine Helper Logic ====
 The internal parameter “time” is available to state machine logic.  It would very useful to create a new parameter called “StateTime” that would reset to zero at each state change.  This would make it much more straightforward to create transitional “timer” states.  Note, assuming the state value is made available as an output, it is possible using a b-source to create a "state-time" node that is based on the state value as follows: