Differential Voltage Generator [Part II]

.tran

• Simulates the time-domain behavior of a circuit.

• Tracks how voltages and currents change dynamically;

• in response to sources (ramps, pulses, sinusoids);

• over a specified time interval.

• Called “Transient Analysis“

.op

• Finds the DC operating point of the circuit.

• Calculates node voltages, currents, and power with all capacitors open-circuited and inductors short-circuited.

• Useful for bias points of transistors or op-amps.

• Called “Operating Point Analysis“

DC Operating Point (in .op analysis)

• The steady-state conditions of the circuit when only DC sources are active.

• It’s like a snapshot of all node voltages and branch currents after the circuit has “settled,” with capacitors treated as open circuits and inductors as short circuits.

• This tells you the bias voltages and currents that active devices like transistors or op-amps will start from before any signals are applied.

.ac

• Computes the small-signal frequency response of the circuit

• Sweeps across frequencies to show gain and phase

• Capacitors and inductors are treated as frequency-dependent impedances.

• Called “AC Analysis“

.dc

• Sweeps a DC source (voltage or current) through a specified range

• Plots the circuit’s steady-state response.

• Useful for I–V curves, transfer characteristics, or resistor networks.

• Called “DC Sweep Analysis“

.trans 10ms

Runs a transient analysis for 10 milliseconds, solving the circuit as voltages/currents change over time.

V

Inside the LTspice, the line must begin with this letter to define an independent voltage source.

Vname +node -node value_or_waveform

Provide the format of defining any independent voltage source inside the LTspice.

vcc VCC 0 15

Voltage source named vcc that sets node VCC to +15 V relative to ground (node 0).

vee VEE 0 -15

Voltage source named vee that sets node VEE to –15 V relative to ground. (Creates ±15 V rails with VCC.)

Linear Ramp

A voltage or current source that changes steadily at a constant rate over time, forming a straight-line slope on a graph. In LTspice, it’s made using a PWL definition

vdm VDM 0 PWL 0 -1 10ms 1

Voltage source vdm on node VDM with a piece-wise linear waveform:
at t = 0 → –1 V; at t = 10 ms → +1 V (a linear ramp).

PWL (Piece-Wise Linear) Source

A way to define a voltage or current source in LTspice by giving it a list of time–value pairs. LTspice connects these points with straight lines, creating a waveform.

Node 0 (Ground in SPICE)

In LTspice, node 0 is always the ground reference point i.e. the “zero volts” line of the whole circuit. Every voltage in the simulation is measured relative to node 0, unless explicitly measured between two other nodes.

C

First letter that represents the capacitor inside the LTspice

X

First letter that represents the subcircuit instance inside the LTspice

Yes. it is true.

Is it true that we don’t really have “two different” nodes (vcc vs VCC). We just have one node, shown in two different letter cases?

1e-3

Meaning of bare ‘m’ in LTspice

suffixes

Numbers/Values accept _______ in the LTspice

.inc LF347_model.txt

Includes an external text file that contains the LF347 op-amp subcircuit/model so the U1A/U1B symbols behave like real devices.

Rail Definition Strategy (± Power Rails)

In circuits with op-amps, we often need both a positive and a negative supply so the output can swing above and below 0 V.

Sources in Directive Block

In LTspice, you can define voltage/current sources either as symbols or as text lines. Writing them as text (e.g., vcc VCC 0 15) in the directive block is just a compact way to keep power rails and test waveforms listed with your analysis commands, instead of adding extra source symbols to the drawing.