Amplifier Gain Compensation Using PTAT Bias and Matched Trimming
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional signal processing devices with cascaded transconductance and transimpedance amplifier stages face challenges in maintaining consistent gain across process and temperature variations, requiring adjustments to trimmable resistors that alter signal bandwidth and gain linearly.
Innovation Solution
A signal processing device with a transconductance amplifier circuit, a transimpedance amplifier circuit, and a bias circuit using first and second transistors connected to a PTAT current source, along with a feedback circuit with a trimmable resistor, where the ratio of resistances between the second and third trimmable resistors is kept constant to maintain gain independence from process and temperature variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a trimmable feedback resistor is used to control bandwidth in the transimpedance amplifier, then signal bandwidth can be kept constant over process variations, but the signal gain changes linearly and total gain becomes dependent on process and temperature variations
Solution Approach 1:
The patent changes the parameters of the bias current by introducing a second trimmable resistor in the bias circuit that can be adjusted independently. This allows the bias current magnitude to be modified, which in turn adjusts the transconductance gain Gm. By changing the bias current parameter, the patent compensates for the gain changes caused by feedback resistor trimming, thereby maintaining stable total gain while preserving bandwidth consistency.
Solution Approach 2:
The patent employs a feedback mechanism where the effect of feedback resistor trimming on gain is compensated by adjusting the bias current through the second trimmable resistor. The system uses the relationship between bias current and transconductance gain as a feedback loop: when R3 is trimmed to maintain bandwidth, the resulting gain change is counteracted by adjusting R2 to restore the original gain level, thus achieving both bandwidth consistency and gain stability.
2Stability of the object's composition
If the resistance of the feedback resistor is trimmed to maintain constant signal bandwidth, then bandwidth consistency is achieved, but the signal gain and total gain become variable
Solution Approach 1:
The patent segments the gain control function into two independent parts: the feedback resistor R3 controls bandwidth, while the second trimmable resistor R2 in the bias circuit controls gain. This segmentation allows independent adjustment of bandwidth and gain without interfering with each other, simplifying the overall control operation despite the additional component.
Solution Approach 2:
The second trimmable resistor R2 acts as an intermediary element that mediates between the feedback resistor trimming operation and the final gain output. When R3 is trimmed to maintain bandwidth, R2 serves as the intermediate adjustment point that compensates for gain changes, thereby simplifying the overall control process by providing a dedicated gain adjustment mechanism.
3Device complexity
If a conventional current mirror arrangement is used in the bias circuit, then the circuit is simple, but it cannot compensate for changes in transimpedance amplifier gain due to process and temperature variations
Solution Approach 1:
The patent transforms the static current mirror arrangement into a dynamic bias circuit by adding the second trimmable resistor R2. This modification enables the bias current to be dynamically adjusted to compensate for gain variations caused by process and temperature changes, while maintaining relatively simple circuit structure that builds upon the conventional current mirror topology.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution ensures that the total gain of the device remains constant despite process and temperature variations, improving the current mirror arrangement and allowing for variable degeneration of the bias current to compensate for changes in the transimpedance amplifier gain.
Implementation Method 1
a reference current input configured to receive a reference current from a proportional-to-absolute-temperature current source
Data Source
AI summary
A signal processing device is configured to compensate for process and temperature variations deviating from a nominal process and temperature condition. A transconductance amplifier circuit produces a current output dependent on a voltage input and a transconductance gain. A transimpedance amplifier circuit produces a voltage output dependent on the current. A bias circuit comprises transistors (M1, M2) configured such that the gate and drain of the first transistor (M1) are connected to the gate of the second transistor (M2) and to a PTAT current source. The source of the first transistor (M1) is connected to a node via a first resistor (R1), and the source of the second transistor (M2) is connected to that node via a second, trimmable resistor (R2). A feedback circuit for the transimpedance amplifier comprises a third, trimmable resistor (R3). The ratio between a resistance of the second and third resistors (R2, R3) is constant.