| 摘要 |
1513448 Transistor amplifier PHILIPS ELECTRONIC & ASSOCIATED INDUSTRIES Ltd 10 Oct 1975 [14 Oct 1974] 41627/75 Heading H3T To convert from a single-ended input to pushpull output, with a predetermined direct current level through each of the two output terminals, the input I is taken to a transistor T l within its emitter circuit the high impedance output of a current mirror transistor T 4 shunted by a D.C.-blocking branch C, R 3 , while the low impedance input D 1 of the current mirror is connected with an impedance R 2 in the emitter circuit of a transistor T 3 of the same conductivity type as T 1 : the collector of T 1 taken via an impedance R 1 and a transistor T 2 provides one push-pull output 2, the base 4 of T 2 being held at fixed potential, while the collector of T 3 provides the second push-pull output 3. The transistor T 4 will normally be matched in emitter area to diode D 1 , which particularly in an integrated circuit may be a diode-connected transistor, to equalize their currents; a non-unity ratio may be adopted if required. The direct current component I o through output 3 and diode D 1 is set by the voltage applied to terminal 4, dropped across the base-emitter junctions of T 2 and T 3 and across diode D 1 and impedances R 1 , R 2 ; through output 2, transistor T 2 and impedance R 1 the current is I u which the current mirror holds equal to I o (unless another ratio is enforced). Pure alternating signal voltage V i applied to terminal 1 produces instantaneous current i through T 2 , R 1 , T 1 causing a change of voltage at the base T, of -iR 1 , and current through D 1 of -iR 1 /R 2 : if R 1 and R 2 are made equal the A.C. through output 3 will be equal and opposite to that through output 4. The two currents +i and -i combine as 2i through C and R 3 , the current i being determined by R 3 since i=Vi/2R 3 ; i.e. the signal gain may be controlled by R 3 independently of the D.C. level through the output terminals. Alternatively (Fig. 2, not shown) the input may be injected in series with R 3 , in which case any direct component in the input signal need not be blocked; the current i will then depend on both R 3 and the transconductance of T 1 . Some or all of the transistors may be FET's; all the resistors may be replaced by frequency dependent impedances. Resistance R 2 may be included with diode D 1 . |
