Bridge-output amplifier with direct-coupled differential-mode feedback

DETAILED DESCRIPTION A source 5 supplies an input signal potential v.
sub.
IN, which is coupled through capacitor 7 to terminal T.
sub.
1 of the bridge-output amplifier shown in FIG.
1.
The input signal v.
sub.
IN is applied to the non-inverting input circuit of a difference amplifier 10, which has an inverting input circuit connected as shall be described to receive overall feedback.
Difference amplifier 10 provides an amplified response to the error signal developed by the subtraction of its input signals--that is, to the input signal v.
sub.
IN as degenerated by the overall feedback.
This response is applied to the input circuit of a cascade of amplifiers 11, 12, 13, which are provided a local a-c feedback connection via the series RC combination 14, for further amplification.
The further amplified degenerated input signal is then applied to limiting circuitry 15 for conversion to a bidirectional signal current with symmetrical limitations as to its maximum positive and maximum negative excursions.
This bidirectional signal current is suitable for application to the parallelled input circuits of phase-splitting amplifiers 20 and 25.
Each of these parallelled input circuits accepts a half of this bidirectional signal current and responds thereto to provide a pair of Class B push-pull output currents.
The phase-splitting amplifiers 20, 25 are each of the type described in U.
S.
Pat.
No.
3,573,645, entitled "PHASE-SPLITTING AMPLIFIER"; issued Apr.
6, 1971 to the present inventor Carl Franklin Wheatley, Jr.
, and assigned to RCA Corporation.
The pair of Class B push-pull output currents provided by phase-splitting amplifier 20 are applied to the base electrodes of transistors 41 and 42, respectively, which transistors are connected as a first push-pull amplifier of the bridge-output output amplifier stage 40 to supply an output signal at terminal T.
sub.
2.
The pair of Class B push-pull output currents of phase-splitting amplifier 25 are applied to the base electrodes of transistors 43 and 44, respectively