LTspice（11） arbitrary behavioral source
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LTspice（11） arbitrary behavioral source
在电子系统里我们需要的信号多种多样，所以为了更加准确的仿真，输入信号应该也是多种多样。在LTspice里通常的电压源支持的模式虽然比较多，但是还不够全面。
常规的电压源可选配置如下⬇️
图1:常规电压源可选配置
如果你的信号超出了这个的定义范围，那么就需要使用arbitrary voltage，在SPICE里面他的开头是B可以是BV也可以是BI分别代表随机电压和电流。以下给出了帮助里的说明。
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B. Arbitrary Behavioral Voltage or Current Sources
Symbol names: BV, BI
Syntax: Bnnn n001 n002 V=<expression> [ic=<value>]
+ [tripdv=<value>] [tripdt=<value>]
+ [laplace=<expression> [window=<time>]
+ [nfft=<number>] [mtol=<number>]]
Bnnn n001 n002 I=<expression> [ic=<value>]
+ [tripdv=<value>] [tripdt=<value>] [Rpar=<value>]
+ [laplace=<expression> [window=<time>]
+ [nfft=<number>] [mtol=<number>]]
The first syntax specifies a behavioral voltage source and the next is a behavioral current source. For the current source, a parallel resistance may be specified with the Rpar instance parameter.
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在任意行为仿真源（arbitrary behavioral source）中 time代表当前仿真时间pi代表
3.14159265358979323846.可以使用LTspice几乎所有的表达式，支持的表达式如下所示。
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Function Name
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Description
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abs(x)
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Absolute value of x
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absdelay(x,t[,tmax])
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x delayed by t. Optional max delay notification tmax.
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acos(x)
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Real part of the arc cosine of x, e.g., acos(-5) returns 3.14159, not 3.14159+2.29243i
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arccos(x)
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Synonym for acos()
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acosh(x)
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Real part of the arc hyperbolic cosine of x, e.g., acosh(.5) returns 0, not 1.0472i
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asin(x)
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Real part of the arc sine of x, asin(-5) is -1.57080, not -1.57080+2.29243i
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arcsin(x)
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Synonym for asin()
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asinh(x)
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Arc hyperbolic sine
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atan(x)
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Arc tangent of x
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arctan(x)
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Synonym for atan()
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atan2(y,x)
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Four quadrant arc tangent of y/x
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atanh(x)
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Arc hyperbolic tangent
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buf(x)
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1 if x > .5, else 0
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ceil(x)
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Integer equal or greater than x
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cos(x)
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Cosine of x
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cosh(x)
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Hyperbolic cosine of x
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ddt(x)
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Time derivative of x
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delay(x,t[,tmax]
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Same as absdelay()
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dnlim(x,y,z)
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Similar to max(x,y) but with a continuous 1st derivative transition width z
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exp(x)
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e to the x
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floor(x)
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Integer equal to or less than x
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hypot(x,y)
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sqrt(x**2 + y**2)
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idt(x[,ic[,a]])
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Integrate x, optional initial condition ic, reset if a is true.
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idtmod(x[,ic[,m[,o]]]
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Integrate x, optional initial condition ic, reset on reaching modulus m, offset output by o.
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if(x,y,z)
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If x > .5, then y else z
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int(x)
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Convert x to integer
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inv(x)
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0. if x > .5, else 1.
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limit(x,y,z)
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Intermediate value of x, y, and z
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ln(x)
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Natural logarithm of x
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log(x)
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Alternate syntax for ln()
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log10(x)
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Base 10 logarithm
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max(x,y)
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The greater of x or y
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min(x,y)
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The smaller of x or y
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pow(x,y)
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Real part of x**y, e.g., pow(-1,.5)=0, not i.
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pwr(x,y)
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abs(x)**y
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pwrs(x,y)
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sgn(x)*abs(x)**y
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rand(x)
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Random number between 0 and 1 depending on the integer value of x.
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random(x)
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Similar to rand(), but smoothly transitions between values.
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round(x)
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Nearest integer to x
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sdt(x[,ic[,assert]])
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Alternate syntax for idt()
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sgn(x)
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Sign of x
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sin(x)
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Sine of x
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sinh(x)
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Hyperbolic sine of x
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smallsig()
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Returns 1 if a .ac or .noise analysis is being done. Otherwise 0.
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sqrt(x)
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Square root of x
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table(x,a,b,c,d,...)
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Interpolate a value for x based on a look up table given as a set of pairs of points.
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tan(x)
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Tangent of x.
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tanh(x)
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Hyperbolic tangent of x
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u(x)
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Unit step, i.e., 1 if x > 0., else 0.
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uplim(x,y,z)
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Similar to min(x,y) but with a continuous 1st derivative transition width z
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uramp(x)
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x if x > 0., else 0.
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white(x)
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Random number between -.5 and .5 smoothly transitions between values even more smoothly than random().
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!(x)
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Alternative syntax for inv(x)
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~(x)
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Alternative syntax for inv(x)
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• The following operations, grouped in reverse order of precedence of evaluation:
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Operand
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Description
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&
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Convert the expressions to either side to Boolean, then AND.
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Convert the expressions to either side to Boolean, then OR.
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^
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Convert the expressions to either side to Boolean, then XOR.
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>
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True if expression on the left is greater than the expression on the right, otherwise false.
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<
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True if expression on the left is less than the expression on the right, otherwise false.
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>=
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True if expression on the left is greater than or equal the expression on the right, otherwise false.
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<=
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True if expression on the left is less than or equal the expression on the right, otherwise false.
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+
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Floating point addition
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-
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Floating point subtraction
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*
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Floating point multiplication
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/
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Floating point division
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**
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Raise left hand side to power of right hand side. Only the real part is returned, e.g., -1**1.5 gives zero not i.
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!
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Convert the following expression to Boolean and invert.
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了解了大概咋回事，咱们就开始搭建一个简单的任意电压源（arbitrary behavioral voltage source）吧！
在LTspice的器件库中直接搜索bv即可，如图2所示。
图2:任意行为电压源
放置好以后我们就可以对其进行测试，我们可以弄个以时间变化的电压值。如图3所示,仿真结果如图4所示。
图3:随时间变化的电压
图4:仿真结果
也许我们想来个随机信号，那我们只要将随机信号的公式带入即可。我们使用random（x）函数，对于它的描述如下所示。
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rand(x)
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Random number between 0 and 1 depending on the integer value of x.
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random(x)
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Similar to rand(), but smoothly transitions between values.
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他可以生成0～1之间的数，具体取决于x的整数值。设置如图5所示。仿真结果如图6所示。
图5:随机电压设置
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