Gain selectable amplifier with resonance compensation

A resonance compensated feedback amplifier, comprising:

• a pair of emitter-coupled transistors forming a differential input stage, a first transistor of the emitter-coupled pair receiving at its base an input signal voltage;
• an output transistor to provide unity voltage gain, the transistor having its base coupled to the collector of a second transistor of the emitter-coupled pair and its emitter coupled to the base of the second transistor to feedback the output voltage to the differential input stage to cause the output voltage to match the input signal voltage;
• and
• a series resonance circuit comprising capacitive and inductive elements coupled across the input stage and output transistor for compensating for the resonance of the emitter-coupled transistors and output transistor created by the feedback, the reactance of the series resonance circuit adjusted to counter gain peaking at the resonant frequency of the amplifier.

A gain selectable feedback amplifier, comprising:

• a differential input stage for receiving an input signal;
• an output stage coupled to the differential input stage to provide current gain to the input signal, an output voltage of the output stage fed back to the differential input stage to cause the output voltage to match the input signal;
• a resistive network coupled to the output stage;
• and
• means for adjusting the gain of the amplifier by varying the resistance of the resistive network.

A gain selectable amplifier with resonance compensation, comprising:

• a pair of emitter-coupled transistors forming a differential input stage, a first transistor of the emitter-coupled pair receiving at its base an input signal voltage;
• an output transistor providing current gain at its collector and unity voltage gain at its emitter, the base of the output transistor coupled to the collector of the second transistor of the emitter-coupled pair and the emitter of the output transistor coupled to the base of the second transistor to feed back the output voltage to the differential input stage to cause the output voltage to match the input signal voltage;
• a series resonance circuit comprising capacitive and inductive elements for compensating for the resonance of the emitter-coupled transistor and the output transistor created by feedback, the reactance of the series resonance circuit adjusted to be substantially zero at the resonant frequency of the amplifier;
• a resistive network of resistive elements coupled to the emitter of the output transistor for selectively setting the current gain of the output transistor;
• and
• a plurality of current sources, each source coupled to a separate resistive element, for selecting the resistance to be applied to the output transistor emitter by activating at least one current source.