09-12-2025: Design of noise performance

09-12-2025: Design of noise performance#

Lecture: EE4109-9

Location: Pulse-Hall 5 (33.A1.200)

Time: 15:45 - 17:30

color coded resistors

Design considerations noise performance#

A systems engineering approach to the design of the noise performance. In a top-down design approach we split error budgets, given as design input over the error contributers of sub circuits assigned during that design step.

Top-down noise budget distribution#

During the first design step, we design the feedback structure of the amplifier that performs the source-to-load signal transfer with the performance-to-costs ratio. At this top-level we have three noise contributers:

  1. The signal source

    The noise associated with the signal source should be known at the start of the design. Hence, this sub-budget is not free to select.

  2. The feedback network

    If the feedback network comprises passive elements, it contributes noise. A sub-budget must be assigned for this contribution. It sets a limit to the values of the feedback elements. The opposite limit (upper/lower) is found from the budget for the power dissipation in the feedback elements. In passive feedback amplifiers, there may exist a conflict of specifications (show-stopper) for noise and power dissipation.

    Noise design equations for the feedback elements can be found using an amplifier model with noisy feedback elements and nullors as controllers.

  3. The controller

    There are multiple contributers to the controller noise:

    1. Signal path noise contributers

      1. Noise of the input stage

        If the input stage is a nullor-like stage (CS stage, anti-series CS stage or complementary-parallel CS stage) the noise of subsequent stages is not dominant. Hence the largest sub-sub-sub-budget at this hierarchical level is assigned to contribition of the input stage of the controller to the output noise of the amplifier.

      2. Noise of subsequent stages

        The noise contribution of subsequent stages should nor be dominant. Hence, a minor sub-sub-budget can be assigend to it.

    2. Noise of the biasing

      Like the subsequent stages, noise of the biasing should not be dominant. Minor budgets can be assigend to them.

      Noise of the biasing consists of:

      1. Noise transferred from the power supply (PSRR)

        The function of the biasing is to provide sufficiently accurate defined operating conditions for the signal path of the amplifier over the specified range of the power supply. Hence, the conversion from power supply variations to signal variations should be low enough (PSRR). If this is not possible, power supply filtering may be an option. A budget must be assigned for the transfer of power supply noise to the output signal.

      2. Noise of the bias sources

        As stated before, noise of the biasing circuitry should not be dominant. A minor budget can be assigend to it.

The design exercise (presentation)#

During the first part of this lecture we will present the first steps in the design of the hearing loop receive coil amplifier:

  1. Setting-up the specifications and a functional model with the amplifier modeled as an integrating voltage-controlled voltage source

  2. Checking of the model and the specifications

    1. The transfer characteristics: gain, frequency characteristic over the frequency range of interest, and possible resonances

    2. The signal source's contribution to DIN-A weighted output noise

Please download the design project archive, unzip it, and open the notebook specifications.ipynb.

Group exercises#

During the second part of this lecture, students work in design teams to achieve the following:

  1. Copy the Kicad schematic of the functional model and replace the integrating voltage-controlled voltage source with a feedback amplifier concept:

    1. This feedback amplifier must have the desired transfer over the frequency range of interest

    2. The feedback amplifier concept uses a noise-free nullor as controller and passive feedback elements (resistors, capacitors, inductors)

    3. The ADC will be DC coupled to the output of this amplifier and the ADC input signal should be within the specified operating range of the ADC

    4. The DIN-A weighted RMS output noise of this amplifier concept, including the noise contribution of the source should not exceed 25% of the total noise budget

    5. The peak current that the controller must deliver to the feedback network does not exceed more than 25% of the supply current budget

    6. Assign numeric values to the feedback network elements and check the amplifier concept's performance (noise, DC operating voltage, frequency response and drive requirements)

    All the above can be done using hand calculations, but you are kindly invited to create a notebook and let SLiCAP derive and solve the necessary design equations in such that a change in the specifications automatically yields updated component values.

  2. Use the circuit with the noise-free nullor and the feedback network from above, specify a gm/ID ratio, assign a current budget for the input stage transistor, and determine W and L of the input stage transistor for the following cases:

    1. NMOS18 CS-stage

    2. PMOS18 CS-stage

    3. NMOS18 differential-pair

    4. PMOS18 differential-pair

    You can use the script and follow the noise design example MOSdesign.py from the downloaded archive.

Contents