A Tour of the Analog Gates

   1.  Clock Icon (TIME).  This displays the current time and timestep.
       It also has a square in the center that changes color to indicate
       how the simulation is going:

            Black       Simulation is turned off
            Red         Computing the next timestep
            Yellow      A timestep has been computed

       If you configure the clock icon you will find that it can
       display a few other time-related values, of interest mostly
       to AnaLOG implementors only.  Note that TIME is not actually
       part of the analog simulator---you can use it for the digital
       simulator, too, but it's not very useful there since the
       digital simulator has such a crude concept of time.

   2.  VDD and GND.  Global power supply.  VDD defaults to +5V.
       You can change the value of Vdd in the NUMBERS gate, but
       Gnd is always zero, and Vdd is always positive. Vdd is an
       idealized voltage source, that is able to source infinite
       current; likewise, Gnd can sink infinite current. Use the
       VDIFF or VSWITCH voltage sources if you need a finite 
       output impedance.

   3.  Terminals (TO, FROM).  These are the two arrow-shaped gates
       in the Catalog.  They are equivalent except for appearance.
       They are used for putting names on signals: to name a signal
       FOO, connect a terminal to it, then tap the space next to
       the arrow and type FOO.  If there are several terminals in
       the circuit with the same names, they are all electrically
       connected as if by wires.  Signal names are also used with
       the Scope mode, to be described below.

   4.  Scoreboard (NUMBERS).  This gate serves many purposes.  On
       the screen it displays whether simulation is proceeding and
       why; it gives controls for set/erase/exact/relaxed modes;
       and, when you tap the center bar, it lets you configure
       AnaLOG's "global" parameters, such as the value of VDD and
       the maximum allowable timestep.  More on these parameters

   5.  Transistors. Both three-terminal (NFET7T, PFET7T) and 
       four-terminal (NFET7F, PFET7F) transistor models are 
       provided. Only geometric information and parameter 
       variations are specified on the screens of these gates.
       Other gates control the physical constants (PHYSICAL)
       device technology parameters (DEVTECHP, DEVTECHN), and
       fab-run specific parameter variations (RUNSPEC) of all
       transistors in the FET7 series. In addition, the temperature
       of all FET7 gates can be varied using the THERMAL gate. For
       backward compatibility, earlier MOS models are also available
       (NFET4, PFET4, NFET5, PFET5, PFET6) as well as FET models
       (NSPC1, PSPC1, contributed by Bhusan Gupta) designed to be
       used with the SPICE netlist tool (see LOGSPC section). Bipolar
       transistor gates and a diode gate (NPN1, PNP1, DIODE) are
       experimental Ebers-Moll models. The log/lib/mos.cnf
       and log/lib/models.cnf hold default configuration
       parameters for transistor models. 

   6.  Capacitor (CAPFLOAT).  Typical capacitor, defaults to 1pF.
       Notice that, like all circuit elements, it has a slight
       parasitic capacitance to ground as well as the capacitance
       between the two leads.

   7.  Resistor (RESFLOAT).  A plain linear resistor. When changing the
       resistance value, note that "m" denotes milliohms, and "Meg"
       denotes Megohms; a common mistake is to type "6m" instead of
       "6Meg" to create a 6 MegOhm resistor. For a more VLSI-like resistor,
       see HRES below.

   8.  Transconductance amplifiers (OPAMP, WRAMP).  These are
       simulations of the narrow- and wide-range amplifiers in Carver's
       book.  Their behavior is modelled after the circuits at the
       transistor level (as modelled by AnaLOG's obsolete FET4 series),
       at least if you use them in the normal range of voltages (between
       0 and 5V).  A little red light turns on if the voltages go outside
       the range in which the model is a safe approximation for the "real"
       circuit. Note that the "Iset" pin at the bottom wants a voltage, not
       a current.  If you want to set the current manually, connect
       a voltage source to the pin and also to a standalone (FET4)
       transistor, then measure the current through the transistor.

   9.  Rectifiers (HWR, FWR).  These are half-wave and full-wave
       rectifiers.  An HWR models an OPAMP driving a two-transistor
       current mirror; an FWR models is like a pair of HWR's.

  10.  Horizontal resistor (HRES).  This big ugly thing is the
       "horizontal resistor" circuit, which predates the circuit in
        Carver's book. Obsolete for new designs. 

  11.  Ganglion (GANGLION).  This is the basic ganglion circuit,
       as described in Carver's Book.

  12.  Voltage/current meter (MMETER).  This meter displays the voltage
       on whatever wire or pin it is connected to.  If you configure it
       you can change it to a current meter, in which case it measures
       current into the gate from whatever pin it is connected to.
       (If you connect a current meter to the middle of a wire, it
       doesn't work because the direction of the current is not well-

  13.  Special magic current meter (ISCOPE).  This is a widget for
       use in plotting currents in Scope mode, and will be discussed
       in the later section on Scope mode.

  14.  Voltage source (VDIFF).  This gate creates a differential
       voltage between its two pins (the bottom pin is typically
       connected to ground).  It has a finite output resistance
       (initially 50 ohms), so it is not an "ideal" source in the
       sense of SPICE.  You can use it as a simple DC source with
       a certain voltage (set by configuring the gate), or you can
       set to output a pulsed or sinusoidal waveform.  This is all
       described below, under Input Waveforms.  Voltage sources
       display the current-limiting condition by lighting up a
       little red light, just like the ones on the lab bench!
       They also have a switch, in the lower-right, that you can
       switch to freeze the waveform in time.

  15.  Current source (IDIFF).  Basically a current-sourcing version
       of the voltage source.  It can generate the same kinds of
       waveforms.  It voltage-limits if the voltage across the pins
       goes below the "crowbar voltage," 0.1V by default.

  16.  Step generator (STAIRS).  A voltage source generating a
       stairstep function, which moves from one voltage to another
       in a certain number of steps, then repeats.

  17.  Voltage switch (VSWITCH).  A voltage source that can be
       manually switched between "on" and "off" voltage levels.
       This one also has a tiny switch on its face, this time to
       select which voltage is generated.  It can also be set in
       "monostable" mode, in which a tap on the switch will turn
       it on for a certain period of time, then back off again
       automatically.  Note that voltages here are implicitly
       relative to ground.

  18.  Current switches (ISWITCH1, ISWITCH2).  Current-sourcing and
       current-sinking versions of the VSWITCH.  The current source
       (arrow pointing out) is like an IDIFF connected to VDD, and
       the current sink (arrow pointing in) is like IDIFF connected
       to GND.

  19.  Piece-wise linear two-terminal element (PWL, contributed by
       Harold Levy). Implements an arbitrary two-terminal element,
       with an i-v transfer curve. Cd to the log/lib directory, 
       start analog, and load the file pwl-test.lgf to learn more.

  20.  Resonant tunneling diode (RTD, contributed by Harold Levy).
       Models a class of quantum well devices. 

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