RF Voltage Detector Circuit Thermal Correction
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Solution Overview
Problem
Existing RF signal detectors lack accuracy and linearity in measuring peak voltage levels, particularly at low voltage levels, due to thermal voltage-dependent errors and non-linear responses.
Innovation Solution
A detector circuit that includes a detection transistor and voltage correction circuitry generating first and second voltage corrections based on thermal voltage and voltage differences between the detection transistor and reference transistors, using hyperbolic tangent functions to improve accuracy and linearity without increasing complexity or cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a first bipolar transistor is used as rectifying element and a second bipolar transistor to set up an offsetting dc voltage, then the detector can provide feedback for controlling output signal level, but the detector exhibits thermal voltage-dependent errors and non-linear response particularly at low voltage levels
Solution Approach 1:
The patent introduces a correction mechanism that dynamically adjusts the detected voltage by subtracting a correction voltage proportional to the thermal voltage VT. The correction voltage is generated based on the ratio of currents through the detection transistor and reference transistor, effectively compensating for the non-linear response and thermal voltage dependencies across different operating conditions
Solution Approach 2:
The patent replaces the simple DC offsetting approach with a more sophisticated correction system using a third transistor configured as a current mirror and associated circuitry to generate the correction voltage. This substitution transforms the basic detection mechanism into a precision measurement system that accounts for thermal effects
2Measurement precision
If the current in the second transistor is doubled relative to the first transistor to cancel the VT-dependent error term, then some error compensation is achieved, but the detector still does not provide exact measurement particularly for low voltage levels
Solution Approach 1:
The patent implements a feedback mechanism where the correction voltage is continuously adjusted based on the actual current ratio between the detection transistor and reference transistor. The third transistor and associated circuitry monitor the detection transistor current and generate a correction signal that is subtracted from the raw detection output, creating a closed-loop system that maintains accuracy across varying conditions
Solution Approach 2:
The patent introduces a third transistor configured as a current mirror that acts as an intermediary between the detection transistor and the correction voltage generation. This intermediary device enables precise control and measurement of current ratios without directly altering the primary detection path, allowing for accurate correction voltage generation
3Measurement precision
If voltage correction circuitry is added to improve linearity and accuracy, then detection precision is improved, but circuit complexity increases
Solution Approach 1:
The third transistor is configured to serve multiple functions: it acts as a current mirror to sense the detection transistor current, generates the correction voltage through its associated circuitry, and provides temperature compensation. This multi-functionality reduces the need for additional dedicated components, thereby limiting the increase in overall circuit complexity
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 proposed solution provides improved linearity and accuracy in detecting RF signal peak voltage levels across a range of input signals, closely matching ideal detector outputs even at low voltage levels, with reduced errors compared to existing methods.
Implementation Method 1
a detection transistor Q0 configured to receive the RF input signal
Implementation Method 2
generating a first correction voltage Vcorr1 having a value equal to VT·ln(2)... generating a second correction voltage Vcorr2 having a value equal to k·Id·tanh((VA−VB)U/(2·VT))
Data Source
AI summary
Methods and apparatus are provided for detection of voltage levels of RF signals. A first voltage correction is provided based on a thermal voltage and a second voltage correction is provided based on a voltage difference between a detection transistor, used for the rectification of the RF signal, and a reference transistor, to which the RF signal is not supplied. Based on the first and second voltage corrections, a more accurate detector with greater linearity may be obtained. In an embodiment, the second voltage correction may be generated proportional to a hyperbolic tangent of the voltage difference between two transistors, obtained using an additional pair of transistors configured as a differential pair. Applications include the control of a power amplifier output in a wireless device.