A fully passive frequency contouring amplifier using segregated passive networks to shape the different portions of the signal thus avoiding all phase distortion and permitting the stages to be coupled without coupling capacitors, thus avoiding distortion caused by the nonlinearities of capacitors. In addition, a special DC servo loop is used to drastically reduce DC amplification.

A low pass active filter comprises multiple stages including multiple active devices, circuitry including resistance and capacitance AC coupling the stages in series sequence, and high impedance biasing resistance coupled between the first and last stage inputs, whereby the DC operating point is determined by one active device.

A regenerator for an undersea optical transmission system has a timing extraction circuit for extracting the clock signal from an NRZ PCM signal. The circuit comprises a surface acoustic wave filter (F) which feeds an amplifier which comprises a number of similar cascaded amplifier sections provided by an integrated circuit. The first stage is a grounded base stage (stage 1) and the following sections each include a balanced emitter-follower buffer stage (stage 2) and a balanced long-tailed pair stage (stage 3). Any base and emitter voltages in an amplifier section are minimised if not eliminated by the long-tailed pair having equal emitter and collector loads.

A circuit for amplifying an input signal comprises an operational amplifi a dual operational amplifier, and a buffering operational amplifier all cascaded in the aforementioned order. The first operational amplifier amplifies the input signal with minimum noise degradation, is set up as a non-inverting amplifier stage, and has a local negative feedback loop comprising a resistor and capacitor in parallel. The dual operational amplifier has two amplifying devices. One device forms a second amplifying stage which increases the gain of the pre-amplified input signal and has a local negative feedback loop comprising a resistor. The other device is a third operational amplifier which combines with the buffering operational amplifier to form an amplifying and buffering stage. The third operational amplifier connects in series to the output of the second amplifying stage. The buffering operational amplifier connects in series to the output of the third operational amplifier and buffers the amplified signal at this output. The amplifying and buffering stage has a two-stage feedback loop comprising a resistor connected between the output of the buffering operational amplifier and the inverting input of the third operational amplifier. A four-stage feedback loop includes a resistor and capacitor in parallel and connects between the output of the buffering operational amplifier and the inverting input of the first operational amplifier.

A circuit arrangement for converting an input voltage into a proportional ouput signal, including a converting resistance which is followed by operational amplifier having a feedback resistance. For the purpose of stabilizing the gain of the circuit arrangement with respect to changes in the converting resistance, the latter is formed by connecting two branch resistances in parallel with each other. These branch resistances are series-connected in a bridge circuit to which a direct voltage is supplied from a voltage source. The bridge circuit also includes an operational amplifier and high-quality film resistors and a variable balancing resistance which includes, in series, another film resistor and a field effect transistor. An integrator automatically balances the bridge circuit by controlling the field effect transistor. The balancing resistor. The feedback resistance operational of the amplifier contains, in series, a film resistor which corresponds to the film resistor in the balancing resistance and a field effect transistor which is matched to the field effect transistor (13) in the balancing resistance. The field effect transistors are controlled in parallel by the integrator. The circuit arrangement can be used for processing the output signal of a capacitive voltage transducer.