We introduce a novel switching mechanism that relies on the bistability of a simple nonlinear electrical resonator which incorporates a varactor diode as its capacitive element. The switching action can be made fast and is self-contained in that no further circuitry is necessary. Unlike a flip-flop, whose state is flipped by applying a TTL pulse, this nonlinear switch can be engaged external to the circuit via magnetic, inductive or capacitive coupling; in this way, the switch becomes intrinsically touch-sensitive. Alternatively, the switching action can also be accomplished using frequency-shift-keying (FSK) modulation, which holds the promise of fast manipulation of the memory state. We demonstrate the potential application of these ideas by constructing a touch-sensitive LED lattice.
In digital electronics, the quintessential memory element that can be switched between two states is, of course, the flip-flop. The ubiquitous SR flip-flop, for instance, consists of two crossed NOR (or NAND) gates. When no signal is applied, the state of the flip-flop remains in its previous configuration, and in order to flip it to the other state a brief voltage signal (a TTL pulse) is applied to the respective input.
Here we propose a nonlinear electrical resonator that in some ways acts like a flip-flop. As we show, the switching between its two states is accomplished via either a driver-frequency protocol (FSK modulation), or by bringing a magnet or inductor into the vicinity of the resonator; it can also be switched by capacitive coupling. Once set, the system remembers its state until another switching action is performed. However, unlike a flipflop, the element can be induced to switch from the outside of the circuit. Alternatively, a frequency modulation scheme can be employed for fast switching. Finally, we show the application of this idea by constructing a controllable LED array.
Since the switching action can occur in response to touch (via changing the capacitance) or proximity to a magnet or inductor, this resonator acts like touch-sensitive switch and is perhaps reminiscent of a “touch lamp”. When the metal housing of such a lamp is touched, its effective capacitance is increased. There are then a number of ways to convert capacitance to a digital output [
Recently, enormous progress has been made in the field of capacitive coupling and sensing, and this has led to the development of touch-sensitive LCD screens. Here again, controllers and micro-processors are incorporated to compute the location of the touch on the screen [2,3]. The power of an array of nonlinear resonators proposed here (see discussion of the prototype) is that no such microprocessing is necessary—the switching action is intrinsic, relying primarily on the bistability of the nonlinear resonator.
Alternatively, fast switching can be accomplished by driving the system at a constant frequency, and then for a brief time interval (given by the FSK modulation pulse width) toggling to another nearby frequency. We show that the pulse width can be as small as two oscillation periods. In the resonator used here, the shortest switching pulse was 7 μs, but this time can be considerably reduced in principle by lowering the inductance value or employing varactor diodes of lower effective capacitance. There is little doubt that switching speeds could reach into the gigahertz range by scaling component properties and boosting the resonance frequency.
The idea of exploiting such resonance bistability is, of course, not new in general. It has been proposed and implemented in a number of physical systems, such as in optical cavities [4,5], in spin systems [