Patent GB-1253255-A (GB)
IPC: H03K5/02
Filed: 1969-01-15
Abstract: 1,253,255. Transistor amplifier and switching circuits. INTERNATIONAL BUSINESS MACHINES CORP. 15 Jan., 1969 [17 Jan., 1968], No. 2357/69. Addition to 1,252,661. Heading H3T. A differential amplifier comprises two transistors 1, 2 (Fig. 1) passing currents which are stabilized by series diode-connected transistors 4, 5 and a pair of series arranged diode-connected transistors 6, 7, differential inputs being applied to the emitters of 1 and 2, as from a differential amplifier 10, 11 and the output being derived at 15 from the commoned collectors. The differential amplifier transistors 10, 11 each have a constant current collector supply 30 to 40, delivering one unit of current and have a common emitter supply 12 receiving two units of current so that when the circuit is balanced and the currents e and d are zero. A constant current source 8 supplies one eighth unit of current to a transistor 6 which is identical to transistors 1 and 2 so that the base-emitter currents of all are equal and the collector current of transistor 6 is a substantially oneeighth unit. The collector currents of 1 and 2 are also one-eighth unit and the combined tail current one-quarter unit. A constant current source 16 supplies one-half unit so that the balance of one-quarter unit flows to the output circuit. If the input voltage V2 rises with respect to V1 a current b flows to the right, increasing the current flow through transistor 2 and thus reducing the output current. The increase in transistor 11 current is accompanied by a reduction in a current in transistor 10 which causes a current e to flow to the right from the collector. This reduces the current in transistor 1 by an amount less than the current increase in transistor 2 so that there is a net reduction of current to the output circuit, which reduction can continue to zero value, whereupon the current reverses.  Fig. 2 shows the constant current supply arrangements. A resistor 23 on the right-hand side is chosen to provide two units of current, one unit passing to each of the diode-connected to transistors 25, 26. These transistors are identical to transistors 27 and 28 and carry the same base current so that the collectors of 27 and 28, constituting the constant current sources 13, 14 of Fig. 1, carry one unit of current each. The two units of current in resistor 23 also flow to diode-connected transistor 22 which, in a similar manner, defines two units of current in the collector circuit of transistor 21, constituting constant current source 12 of Fig. 1. A resistor 35 on the left-hand side provides a defined current of one-half unit. This divides between diode-connected transistors 31, 32, 33 and 34 which thus each carry one-eighth unit and so define a current of one-eighth unit in the collector of a transistor 30 constituting the constant current source 8 of Fig. 1. The oneeighth value, for a similar reason, flows in the collectors of transistors 40, 41, 42, 43 which thus together define a current of one half unit in the constant current source 16 of Fig. 1. A circuit 50, 48 and 36 provides a stabilized bias for the left-hand input transistor 10. The output is supplied to an amplifier 45 having a diode feedback circuit to square the output.