A broken chord is a chord whose pitches are played one after the other, as opposed to playing them simultaneously in a block chord.
Most analogue synthesisers are monophonic, so this is the only way to play a chord on them.
The simplest kind of broken chord is an arpeggio, in which the chord's pitches are simply repeatedly played in ascending or descending order. Some synthesisers can automate this with an arpeggiator.
The Alberti bass, popularised by Domenico Alberti, is an everso slightly more complex pattern for primary triads in particular, in which you repeatedly play the lowest pitch, then highest, then middle, then highest again.
A single broken chord is pretty straightforward to play on even an analogue step sequencer — especially with an appropriate quantiser such as Doepfer's A-156 — likely accounting for various electronic songs that feature a single chord throughout their entire runtime. You can even transpose the output to different chords with an electronic adder such as Doeper's A-185-2, albeit without any fancy inversions.
Many variations on this technique sound good, such as the evolving sequence in Kraftwerk's "Europe Endless", or the dual sequences in Donna Summer's "I Feel Love", courtesy of Giorgio Moroder.
By combining a broken chord with a delay effect at an appropriate tempo, you can make multiple pitches appear at the same time, even though they're not technically created at the same time.
- The AB Guide to Music Theory Eric Taylor, 1990, ISBN 1-85472-446-0, p. 66