What is the role of a current mirror in current steering DACs?
1 Answer
In current steering digital-to-analog converters (DACs), a current mirror is a fundamental component that plays a crucial role in converting digital input codes into corresponding analog output currents. A current steering DAC is a type of DAC architecture that uses a binary-weighted current source array to generate different output currents based on the digital input code.
The main function of a current mirror in a current steering DAC is to replicate and control the reference current. The reference current is typically generated based on the most significant bit (MSB) of the digital input code and sets the scale for all the other currents in the DAC.
Here's how a current mirror works in a current steering DAC:
Reference Current Generation: The most significant bit of the digital input code determines whether the highest current or reference current is "on" or "off." If the MSB is set to 1, the reference current source is activated, and if it is set to 0, the reference current source is turned off.
Current Splitting: The reference current is split into two equal parts, and one part goes to the positive (upper) branch of the DAC, while the other goes to the negative (lower) branch.
Digital Code Interpretation: The remaining bits of the digital input code represent different binary-weighted currents. Each subsequent bit represents half the value of the previous one.
Current Steering: Depending on the state of the lower-order bits, switches are used to connect or disconnect the corresponding binary-weighted currents to the branches. The current mirror ensures that each current in the positive branch has an identical counterpart in the negative branch, but with the opposite polarity.
Analog Output: The analog output is obtained by summing all the currents in the branches. The current mirror ensures that the currents are properly matched, and the analog output voltage is a linear combination of these currents, which results in a smoothly varying analog signal representing the digital input code.
The use of a current mirror helps to achieve accurate and precise current matching between the different branches of the DAC, ensuring a high linearity and minimizing errors and mismatches that could otherwise degrade the DAC's performance. This is crucial for maintaining the fidelity of the analog output signal in applications such as audio processing, communication systems, and instrumentation.
The main function of a current mirror in a current steering DAC is to replicate and control the reference current. The reference current is typically generated based on the most significant bit (MSB) of the digital input code and sets the scale for all the other currents in the DAC.
Here's how a current mirror works in a current steering DAC:
Reference Current Generation: The most significant bit of the digital input code determines whether the highest current or reference current is "on" or "off." If the MSB is set to 1, the reference current source is activated, and if it is set to 0, the reference current source is turned off.
Current Splitting: The reference current is split into two equal parts, and one part goes to the positive (upper) branch of the DAC, while the other goes to the negative (lower) branch.
Digital Code Interpretation: The remaining bits of the digital input code represent different binary-weighted currents. Each subsequent bit represents half the value of the previous one.
Current Steering: Depending on the state of the lower-order bits, switches are used to connect or disconnect the corresponding binary-weighted currents to the branches. The current mirror ensures that each current in the positive branch has an identical counterpart in the negative branch, but with the opposite polarity.
Analog Output: The analog output is obtained by summing all the currents in the branches. The current mirror ensures that the currents are properly matched, and the analog output voltage is a linear combination of these currents, which results in a smoothly varying analog signal representing the digital input code.
The use of a current mirror helps to achieve accurate and precise current matching between the different branches of the DAC, ensuring a high linearity and minimizing errors and mismatches that could otherwise degrade the DAC's performance. This is crucial for maintaining the fidelity of the analog output signal in applications such as audio processing, communication systems, and instrumentation.