Wide band constant gain amplifier

A differential amplifier having input terminals and output terminals comprising:

• a differential input stage having first and second input transistors, each of said input transistors having a gate, a source and a drain terminal such that the respective gates of said transistors are coupled so as to receive a different input signal, and the respective sources of said transistors are coupled together and to a first current source;
• an active load stage having first and second load transistors such that the respective sources of said load transistors are coupled together and to a DC biasing voltage source providing a signal with substantially no fluctuation, the respective drains of said load transistors are coupled to the respective drains of said input transistors so as to define said output terminal, and the gates of said load transistors are adapted to receive a bias signal, said gates of said load transistors being substantially isolated from said DC power supply;
• and
• second and third current sources adapted to be coupled to a DC power supply, each of said current sources being coupled to the drains of said input and load transistors so as to substantially isolate noise signals generated by said DC power supply from said output terminals. of said amplifier.

An amplifier comprising:

• a differential input stage for receiving a differential input signal, said differential input stage further comprising input and output terminals;
• an active load stage coupled to a DC power supply, for providing an active load for said differential input stage, wherein said active load stage is substantially isolated from said DC power supply;
• and
• a biasing circuit for biasing said active load stage, such that noise signals attributable to said DC power supply are substantially attenuated at said output terminals and such that the gain of said amplifier remains substantially constant for a substantially predetermined range of operating frequencies.

In an amplifier having input and output terminals and powered by a direct current (DC) power supply, a method for providing a constant gain over a substantially wide frequency range, comprising the steps of:

• receiving a differential input signal by a differential input stage of said amplifier so as to generate an output current signal in response to said input signal, by employing an active load stage coupled to said differential input stage;
• substantially isolating said direct current DC power supply from said active load stage;
• transforming said output current signal to an output voltage signal at said output terminals;
• and
• substantially attenuating noise signals generated by a direct current (DC) power supply coupled to said amplifier by substantially isolating said direct current DC power supply from said output terminals, in a manner so as to substantially reduce the noise signal in said output voltage signal.