These ideas are only springboards for your circuit creativity. And to boot,
there are no single "right" answers. Let the design have several
starts and stops, a few zig-zag paths, its okay, just have fun and get in
So take off
on an idea that strikes your creative spirit. Play with some circuit
elements to get your idea going. Think of the circuit components as Lego
building blocks ( Lego from the Danish word meaning to "play
well".) As a suggestion, take a particular angle on the design: all opamps, only transistors, just SPICE sources with table or equation
definitions, or any other approach you might like.
Let us know
about any interesting circuits that pop out of your design adventures. Share
any challenges and solutions you've encountered. Send us
a netlist and a brief description. (Circuit should be small enough to run on
a demo version.)
1 - SAMPLE AND HOLD AMPLIFIER
Create a sample and hold
circuit using a SPICE Switch or JFET followed by a capacitor. You can also
buffer the output with a high impedance amplifier.
As an example, sample a
1 kHz sinewave with a 10 kHz sampling pulse that's 1us wide. Use the SIN and
PULSE definitions for these waveforms.
Create an oscillator based on a bandpass filter
followed by a comparator stage. The comparator output drives the bandpass
Bandpass filter ideas: LCR
filter, opamp filter with R/Cs only.
transistor, opamp, E source with table definition.
VOLTAGE CONTROLLED GAIN AMPLIFIER
Design an amplifier whose
gain is controlled by an external voltage. The parameters could be anything. As an example: vary the control voltage from 0 to 5V to change the gain from 1 to
Amplifier ideas: An opamp
where one of the gain resistors is made up of a JFET or a SPICE
Switch device (voltage controlled resistance). Or, a transistor differential
pair whose emitter current is controlled by an external voltage.
EXCLUSIVE NOR GATE
Create an Exclusive NOR
gate (output is HI when inputs A AND B are both HI or A AND B are
both LO.) As your building blocks, combine some of the
Basic Digital Gates found in
the circuit collection.
- THERMISTOR AMPLIFIER
Suppose you need to design an amplifier for a thermistor sensor that outputs +0.1 V / deg
C with the output equal to +2.5 V at +25 deg C.
Amplifier ideas: A great
place to start is the
Linearized Thermistor Circuit. Follow this by an opamp whose gain scales
the output to +0.1 V / deg. Use the same or another opamp to shift the
output to +2.5 V at +25 deg C.
- ONE SHOT TIMER
555-Timer from oscillator
mode to one-shot mode. Use a repeating PULSE waveform as the trigger.