Amplifier and Oscillator Circuits Flashcards

Neutralization of an RF amplifier stage is performed to:

Answer: Cancel unwanted feedback caused by the transistor's internal collector-base capacitance

At high frequencies, the transistor's internal capacitance feeds energy back from output to input; neutralization applies equal and opposite feedback to cancel this effect and prevent oscillation.

The 3 dB bandwidth of a single-tuned RF amplifier stage is determined by:

Answer: The ratio of resonant frequency to the circuit Q factor

Bandwidth equals the resonant frequency divided by the Q factor (BW = f₀/Q), so a higher Q circuit results in a narrower, more selective bandwidth.

Intermodulation distortion (IMD) products are generated when:

Answer: Two or more signals pass through a nonlinear device, producing spurious sum and difference frequencies

Nonlinearities in an amplifier or mixer cause multiple input signals to mix, generating spurious output signals at sum, difference, and harmonic combinations of the input frequencies.

Automatic Gain Control (AGC) in a communications receiver is used to:

Answer: Keep the receiver's audio output relatively constant despite varying received signal strength

AGC reduces the gain of the receiver's RF and IF amplifier stages when a strong signal is received, maintaining a relatively constant audio output level.

Why is the noise figure of a receiver's first RF amplifier stage especially critical?

Answer: Noise introduced in the first stage is amplified by all subsequent stages, directly limiting receiver sensitivity

Any noise introduced in the first amplifier stage gets amplified by all subsequent stages, so a low noise figure in the front end is essential for good receiver sensitivity.

The dynamic range of a receiver is defined as the difference between:

Answer: The strongest signal that can be received without distortion and the weakest detectable signal (noise floor)

Dynamic range describes the span of signal levels a receiver can handle simultaneously, from barely detectable weak signals at the noise floor to the strongest signals without generating distortion.

A cascode amplifier configuration uses two transistors to primarily:

Answer: Reduce the Miller effect and improve high-frequency gain stability

The cascode configuration isolates the input transistor's collector from the output load, dramatically reducing Miller capacitance multiplication and improving RF stability and bandwidth.