U.S. Philips Corporation

Johannes Wilhelmus Glasbergen

Dieter Schwarz

Ralf Misner

A circuit arrangement for reproducing in an output circuit (4) a current (i1) flowing in an input circuit (1) comprises a PNP-current mirror (2) to the input (2-1) of which the input circuit (1) is connected. The mirror output (2--2) is connected to the emitter of an output transistor (3) of the PNP-type the collector of which is connected to the output circuit (4). The base of the transistor (3) is connected to the input (5-1) of an NPN-current mirror (5), whose output (5-2) is connected to the input (2-1) of the PNP-current mirror (2), so that the effect of the base current (ib) of the transistor on its collector current will be compensated for.

Circuit arrangement for reproducing in an output circuit a current

An adaptive delta modulator must produce at its output a periodic 0-1 sequence when the input signal (w) to be coded assumes zero value. The delta modulator of the present invention is provided with a generator (GE) to produce a periodic 0-1 sequence which is transmitted to the receiver instead of the delta coded signal when the input signal to be coded assumes zero value. This generator (GE) is switched to the output line of the delta modulator at the instant at which the output voltage (Us) of a filter (IN) in the feedback path of the delta modulator, for determining the instantaneous quantizing unit of the delta modulator, assumes zero value. If this filter (IN) is implemented with digital components, the generator (GE) is triggered by the output pulses of a gate (G1) whose inputs are connected to the respective locations of the input signal storing means of the filter (IN). A delay line (V) prevents triggering of the generator (GE) at extremely short pauses in the input signal (w) to be coded.

Adaptive delta modulator

A pulse code modulation transmission device comprising a transmitter and a receiver each being provided with a dynamic control circuit and a modulator built up of a first controlled current source circuit supplying a supply current for a difference amplifier which is controlled by output pulses from the transmitter and incorporating in its two output circuits pnp current mirror circuits whose outputs are connected to the output of a modulator directly and through a precision polarity reversing circuit, respectively. The control input of the first current source circuit is coupled to the output of the dynamic control circuit as well as to the input of a fourth current source circuit arranged in parallel therewith whose output is connected in the manner of a feedback through a pnp-current mirror circuit to a npn-current mirror circuit whose output is coupled to the output of the dynamic control circuit.

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Hilversum, Netherlands

Johannes Wilhelmus Glasbergen