Abstract: A D/A converter providing a binary weighted series of currents (I.sub.3, I.sub.4, I.sub.5) via first current-source transistors (T.sub.3, T.sub.4, T.sub.5) each in a given ratio to a reference current (I.sub.1) in a reference transistor (T.sub.1). The weighted currents are switched to analog output (15) or to positive supply terminal (20) via first switching devices (3.1, 3.2, 3.3). A control device includes a second current-source transistor (T.sub.8) connected to a reference-current source or to the positive supply terminal via a second switching device (4). The current (I.sub.8) in the transistor T.sub.8 has a given ratio to the reference current (I.sub.1). By connecting the second current-source transistor to the positive supply terminal or to the reference current source, the reference transistor carries the full reference current (I.sub.ref) from the reference current source or only a fraction of the full reference current, respectively. As the weighted currents are in a given ratio to the current (I.

Abstract: For detecting whether an input signal is above or below a reference level in such a way that brief signal interruptions and negative spurious pulses are not interpreted as decreases below the reference level, the detector includes an input comparator, a first delay circuit, a second delay circuit and an output circuit. The first delay circuit comprises a first integrator comprising a first transistor and a first capacitor, a first current source and a second comparator. The second delay circuit comprises a second integrator with a second transistor and a second capacitor, a second current source and a third comparator. The first delay circuit and the second delay circuit have equal delay times.

Abstract: An apparatus is described for reading optically coded discs. In this apparatus the photodiode signals are amplified by current amplifiers which are biased by the unipolar photodiode signal currents, so that offset-free class-B operation is obtained.