1. A voltage- and temperature-insensitive oscillator, comprising: first and second time-delay circuits, each comprising a trip point detector, having an input and having an output which changes state whenever said input is charged to a substantially predetermined trip point voltage, a charging circuit which, when activated, charges said input of said trip point detector, and which includes a first resistance having a first temperature coefficient of resistance, a second resistance which has a second temperature coefficient of resistance different from said first temperature coefficient of resistance, and which is connected to discharge said input of said trip point detector, a capacitance connected to said input of said trip point detector, and a discharging circuit which, when activated, discharges the voltage on said input of said trip point detector, wherein said discharging circuit, when activated, discharges said input from said trip point to a first level more rapidly than said charging circuit, when activated, charges said input from said first level to said trip point; and wherein, when said charging circuit is activated, said capacitance receives one part of the current flowing through said first resistance, and another part of the current flowing through said first resistance flows through said second resistance but is not received by said capacitance; wherein, whenever said trip-point detector of either of said time-delay circuits is activated, said respective discharging circuit thereof is activated, and said charging circuit of the other of said time-delay circuits is also activated; and further comprising an output circuit which combines the respective outputs of said first and second time-delay circuits.