U.S. Philips Corporation

Philips Electronics North America Corporation

Roelof F Wassenaar

Evert Seevinck

Johan Hendrik Huijsing

John P Tero

Eerke Holle

Remco J Wiegerink

Ron Hogervorst

A differential amplifier contains a pair of differential portions (10 and 12) that together provide representative signal amplification across the full amplifier power-supply voltage range. Each differential portion normally contains a pair of like-polarity differentially coupled FETs (Q1 and Q2, Q3 and Q4) that divide a tail current (I.sub.N, I.sub.P) into a pair of main currents (I.sub.1 and I.sub.2, I.sub.3 and I.sub.4). The two FET pairs are complementary. A square-root circuit (24) controls the tail currents in such a way that the sum of their square roots is largely constant. Consequently, the amplifier transconductance is largely constant.

Differential amplifier having rail-to-rail input capability and

A voltage-current converter includes a first current-source (I.sub.1) coupled by means of a diode-arranged first transistor (T.sub.1) to a first terminal (1) at reference potential and by means of a diode-arranged second transistor (T.sub.2) to a second terminal (2). The bases of a third (T.sub.3) and a fourth (T.sub.4) transistor are coupled to the first (1) and the second (2) terminal, respectively. The emitters of these transistors (T.sub.3,T.sub.4) are coupled to a second current source (I.sub.2). A voltage source (V) and a resistor (R.sub.1) for converting the voltage (V) into a signal current are arranged between the first (1) and the second (2) terminal. The signal current is amplified by the translinear-circuit of the first, second, third and fourth transistors (T.sub.1 -T.sub.4) and fed to the outputs (30,40) via cascode transistors (T.sub.9,T.sub.10). To correct the non-linearity in the voltage-current conversion due to the non-linear emitter resistors of the first (T.sub.1) and the second (T.sub.2) transistor, a correction circuit (5) having a negative input resistance is coupled to the first (1) and the second (2) terminal.

Voltage-current converter

An amplifier that supplies a bias current (I.sub.t) which is dependent on an input signal (V.sub.i) to a junction point (2) of the source electrodes of first and second transistors (T.sub.1, T.sub.2). The amplifier comprises a control circuit that limits the bias current so it cannot increase more than is necessary to obtain a high slew rate, thereby minimizing dissipation by the amplifier. This control circuit comprises a third and a fourth transistor (T.sub.3, T.sub.4) arranged in parallel with the first transistor (T.sub.1) and the second transistor (T.sub.2), respectively, and which carry currents (I.sub.3, I.sub.4) which are proportional to the currents (I.sub.1, I.sub.2) in the first and the second transistor. A selection circuit (5) applies the smaller of the two currents (I.sub.3, I.sub.4) in the third and the fourth transistor to an output (8) where this current is compared with a reference current (I.sub.o) from a current source (9). The difference between these currents is applied to a current amplifier ( 10), which supplies an increasing bias current (I.sub.t) until the smaller of the two currents (I.sub.3, I.sub.4) in the third and the fourth transistor equals the reference current.

Amplifier arrangement

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Enschede, Netherlands

Roelof F Wassenaar