Explanation:
The output impedance of a transistor circuit is defined as the ratio of the change in output voltage to the change in output current. It is an important parameter to consider while designing amplifier circuits as it determines the load that can be connected to the circuit without affecting its performance.

The three basic transistor configurations are common base (CB), common emitter (CE), and common collector (CC). Each configuration has its own characteristics and advantages, but when it comes to output impedance, the common base configuration provides the highest output impedance.

Reasons why common base configuration provides highest output impedance:

1. Current gain is low: In common base configuration, the input signal is applied to the emitter and the output is taken from the collector. The base is common to both input and output circuits. The current gain in this configuration is low due to the fact that the base current is small compared to the emitter current. As a result, the output impedance is high.

2. Voltage gain is high: In common base configuration, the voltage gain is high due to the fact that the input impedance is low and the output impedance is high. This makes it suitable for impedance matching applications.

3. Low power output: In common base configuration, the power output is low due to the fact that the collector current is small compared to the emitter current. This makes it suitable for high-frequency applications where low power is required.

Conclusion:
In conclusion, the common base configuration provides the highest output impedance due to its low current gain, high voltage gain, and low power output. This makes it suitable for applications where high input impedance and low output impedance are required.

In Common-Base Transistor, the base-emitter junction JE at input side acts as a forward biased diode. So, the common base amplifier has a low input impedance (low opposition to incoming current). On the other hand, the collector-base junction JC at output side acts somewhat like a reverse biased diode. So the common base amplifier has high output impedance.