Where did the BJT cascode amplifier come from?
Before the invention of the RF dual gate MOSFET, the BJT cascode amplifier could have been found in UHF (ultra high frequency) TV tuners. A cascode amplifier consists of a common-emitter stage loaded by the emitter of a common-base stage.
What are the features of a cascode amplifier?
A cascode amplifier consists of a common-emitter stage loaded by the emitter of a common-base stage. A cascode amplifier has a high gain, moderately high input impedance, a high output impedance, and a high bandwidth.
Which is larger the cascode or the common emitter?
Both the Cascode and Common emitter have large amplitude outputs. The Va point has a DC level of about 10V, about half way between 20V and ground. The signal is larger than can be accounted for by a C-E gain of 1, It is three times larger than expected. Cascode vs common-emitter banwidth.
Is the collector signal out of phase with the base signal?
However, in the C-E configuration, the collector output signal is out of phase with the input at the base. The collector signal capacitively coupled back opposes the base signal. Moreover, the collector feedback is (1-Av) times larger than the base signal. Keep in mind that Av is a negative number for the inverting C-E amplifier.
How to calculate the voltage of a BJT amplifier?
Replace the transistor by its h-parameter model hfb = -0.98, hob = 0.49µA/V, hrb = 2.9*10 -4. Calculate the values of input resistance, output resistance, current gain and voltage gain for the given circuit.
How to analyze the midband of a BJT?
Let us analyze the hybrid model to find current gain, input resistance, voltage gain and output resistance. It is defined as the ratio of output to input current. It is given by, Here IL and I2 are equal in magnitude but opposite in sign. IL = -I2
What kind of bias is used in RF amplifiers?
A very low-cost biasing scheme for RF and microwave circuits, but with less thermal stability than above, is called collector-feedback bias. The circuit, employs only two resistors, along with the active device, and has very little lead inductance due to the emitter’s direct connection to ground.
When do you bias a bipolar junction transistor?
Biasing Considerations for RF Bipolar Junction Transistors (BJT) Usually the manufacturer supplies in their datasheets a curve showing ft versus collector current for a bipolar transistor. For good gain characteristics, it is necessary to bias the transistor at a collector current that results in maximum or near-maximum ft.
How is the BJT differential pair a differential amplifier?
The differential pair is a differential amplifier—we express its performance in terms of differential and common-mode gains. Consider the BJT differential pair: 2 1 Also, we know that: Therefore, the emitter currents can be written in terms of the base voltages as: Of course, we know that Ii i= EE12+ , thus: