GB1319859A - Feedback amplifier circuit - Google Patents

Abstract

1319859 Feedback amplifiers; sawtooth wave generators TEKTRONIX Inc 9 July 1970 [24 July 1969] 33290/70 Heading H3T A cascode transistor amplifier has negative feedback from the output to the input via an emitter follower and a series resistor. Fig. 2 shows the cascode amplifier feeding sawtooth waves to the deflection electrode 18 of a cathoderay tube. 32 is a constant current load transistor and 24 is a feedback amplifier included to reduce the load otherwise provided by resistor 26 on the output circuit so that the capacitance of the deflection electrodes can be more quickly charged. Fig. 3 is a similar circuit in which the first stage 10 of the cascode is coupled to the series transistors for high frequencies via a capacitor 50 and for lower frequencies via a common base stage 40. Capacitor 56 provides drive for the constant current transistor 32 to cut it off during the negative slope and to enhance its current during the positive slope. The opposite polarity drive for the other deflection plate may be obtained from a similar circuit (Fig. 4, not shown) using a transistor (10<SP>1</SP>) of opposite conductivity type and using the upper transistor (54<SP>1</SP>) as the main input stage of the cascode. Fig. 5 (not shown) illustrates the combination of circuits similar to Figs. 3 and 4. It includes diodes (62, 64) biased from a potentiometer (70) to equalize and adjust the bias to the input stages (10, 10<SP>1</SP>). The diodes are shunted by a capacitor (66) to ensure cancellation of the transients to the input transistors (10, 10<SP>1</SP>) and output transistors (24, 24<SP>1</SP>). A capacitor (72) across the feedback resistor adjusts the feedback phase, capacitors (76, 78, 82) across voltage dividers and an adjustable resistor (80) in the voltage divider optimize the high frequency performance.