The modulation technique that usually requires minimum bandwidth in digital transmission is Pulse Amplitude Modulation (PAM).

Pulse Amplitude Modulation (PAM) is a modulation technique used in digital transmission where the amplitude of a series of regularly spaced pulses is varied in accordance with the instantaneous amplitude of the modulation signal. PAM is the simplest form of pulse modulation and is widely used in communication systems.

Advantages of PAM:
1. Simple Implementation: PAM is relatively simple to implement compared to other modulation techniques. It only requires a pulse generator and a modulator circuit, making it cost-effective and straightforward to design.

2. Efficient Bandwidth Utilization: PAM has the advantage of efficient bandwidth utilization. The bandwidth required for PAM is equal to the Nyquist bandwidth, which is twice the highest frequency component of the modulating signal. Since PAM only involves varying the amplitude of pulses, it does not require additional frequency bands for modulation. This makes PAM an efficient modulation technique for transmitting digital signals.

3. Immunity to Noise: PAM signals have good noise immunity characteristics. Since PAM signals are transmitted as discrete pulses, they can be easily reconstructed at the receiver end. The receiver only needs to sample the received pulses at the correct time to recover the original signal, reducing the impact of noise and interference.

4. Compatibility with Digital Systems: PAM is compatible with digital systems and can be easily integrated with digital signal processing techniques. It allows for easy conversion between analog and digital signals, making it suitable for various applications such as digital audio transmission, data communication, and image transmission.

Comparison with Other Modulation Techniques:
- Delta Modulation (DM): Delta modulation is a form of differential pulse code modulation (DPCM), where the difference between the input signal and its quantized approximation is encoded. Delta modulation requires a higher bandwidth compared to PAM due to the additional information carried by the difference signal.

- Pulse Code Modulation (PCM): PCM is a digital modulation technique where the amplitude of the analog signal is quantized and encoded into digital data. PCM requires a higher bandwidth compared to PAM since it involves sampling the analog signal at a higher rate and quantizing the samples.

- Differential Pulse Code Modulation (DPCM): DPCM is a modification of PCM where the difference between the current and predicted sample is encoded. DPCM requires a higher bandwidth compared to PAM due to the additional information carried by the difference signal.

In conclusion, Pulse Amplitude Modulation (PAM) is a modulation technique that usually requires minimum bandwidth in digital transmission. It offers efficient bandwidth utilization, simple implementation, noise immunity, and compatibility with digital systems. PAM is widely used in various communication applications due to its advantages in transmitting digital signals effectively.