Reconnection-less OTA-based Biquad Filter with Electronically Reconfigurable Transfers
At a Glance
Section titled âAt a Glanceâ| Metadata | Details |
|---|---|
| Publication Date | 2015-06-11 |
| Journal | Elektronika ir Elektrotechnika |
| Authors | Roman Ć otner, JiĆĂ PetrĆŸela, Jan JeĆĂĄbek, TomĂĄĆĄ DostĂĄl |
| Institutions | College of Polytechnics Jihlava, Brno University of Technology |
| Citations | 30 |
| Analysis | Full AI Review Included |
Technical Documentation and Analysis: Diamond-Enabled Reconfigurable Biquad Filters
Section titled âTechnical Documentation and Analysis: Diamond-Enabled Reconfigurable Biquad FiltersâReference: Sotner et al. (2015). Reconnection-less OTA-based Biquad Filter with Electronically Reconfigurable Transfers. ELEKTRONIKA IR ELEKTROTECHNIKA, VOL. 21, NO. 3.
Executive Summary
Section titled âExecutive SummaryâThis paper presents a robust, second-order, active voltage-mode biquad filter leveraging Operational Transconductance Amplifiers (OTAs) for high-speed, electronically reconfigurable signal processing. Crucially, the experimental validation relied on active devices fabricated on advanced materials, directly aligning with 6CCVDâs expertise in high-performance CVD diamond substrates.
- Core Achievement: Demonstrated a reconnection-less technique for instantaneously changing the filter transfer function (e.g., All-Pass, Band-Reject, High-Pass, Low-Pass with zero).
- Electronic Control: Filter type, quality factor (Q), and tuning are achieved exclusively by electronically adjusting the transconductances (gm) of the OTAs.
- Enabling Material: Measurement results were confirmed using specialized Diamond Transistors, validating the designâs viability for high-frequency applications.
- Frequency Range: Operation confirmed across a wide band, from several kHz up to several tens of MHz.
- Synthesis Method: Utilized the Matrix Method of Unknown Nodal Voltages (MUNV) to ensure design readiness for immediate CMOS integration.
- Applications: Ideal for high-speed signal processing where continuous, smooth variability and immediate transfer function modification are necessary, such as active noise cancellation or complex electronic systems.
Technical Specifications
Section titled âTechnical SpecificationsâThe following hard parameters define the performance and operational conditions of the tested biquad filter circuit:
| Parameter | Value | Unit | Context |
|---|---|---|---|
| Active Elements | 4 | Units | Required OTAs for reconnection-less reconfiguration |
| Active Device Material | Diamond Transistors | N/A | Used for high-frequency, experimental verification |
| Nominal Supply Voltage (VDD/VSS) | ±5 | V | Standard dual-rail operation |
| Nominal Capacitors (Câ, Câ) | 470 | pF | Working values used in the experimental setup |
| Ideal Pole Frequency (fp) | 339 | kHz | Designed frequency at nominal Q=1 |
| Filter Operation Range | kHz to Tens of MHz | N/A | Confirmed functional frequency spectrum |
| Nominal Transconductance (gm1,2) | 0.91 | mS | Set electronically via degradation resistors (Rdeg) |
| Maximum Attenuation (Band-Reject) | 40 | dB | Achieved at gm3 = 0.1 mS |
| Input Power Level (Measurement) | -15 | dBm | Corresponds to 40 mVef on 50 Ω |
| Available Transfers | 6 | Types | AP, BR, HP, iBP, HPZ, LPZ (all electronically switchable) |
Key Methodologies
Section titled âKey MethodologiesâThe synthesis and experimental validation relied on precise control over nodal voltages and transconductance parameters, made stable by the high-performance active devices.
- Synthesis: The design started with a highly general second-order voltage transfer function, enabling independent pole and zero placement, essential for full reconfigurability.
- Circuit Derivation: The Matrix Method of Unknown Nodal Voltages (MUNV) was applied to solve the linear non-homogeneous equations, leading to the required three independent nodes and the final admittance matrix (Y).
- Active Device Selection: Five high-frequency diamond transistors (OPA860 family) were implemented as single-output OTAs and voltage buffers.
- Parameter Control: The electronic transconductance (gm) for each OTA was controlled by varying external passive degradation resistors (Rdeg), enabling fine-tuning of filter coefficients.
- Reconfiguration Mechanism: Transfer function change (reconfiguration) was achieved solely by setting the required gm ratios (e.g., $g_{m1}=g_{m2}=g_{m3}=g_{m4}$ for All-Pass, or $g_{m3} \rightarrow 0$ for High-Pass).
- Validation: Filter performance, stability, and transfer responses were measured using a vector/spectrum analyzer (HP4395A) across the MHz range.
6CCVD Solutions & Capabilities
Section titled â6CCVD Solutions & CapabilitiesâThe successful realization of this high-performance, high-frequency active filter hinges on the stability and speed provided by the active diamond transistors. 6CCVD is positioned as the primary supplier for the enabling material technology necessary to replicate or advance this research toward integrated solutions (CMOS integration).
Applicable Materials
Section titled âApplicable MaterialsâThe high-frequency operation and stability requirements necessitate high-quality MPCVD diamond substrates.
| Application Requirement | Recommended 6CCVD Material | Rationale & Benefit |
|---|---|---|
| High-Performance Active Devices (OTAs) | Optical Grade SCD (Single Crystal Diamond) | Required for high electron mobility, extreme thermal management, and stability critical for high-speed transistor fabrication (up to 125mm possible). |
| Integrated Thin-Film Solutions | Thin SCD Films (0.1 ”m - 50 ”m) | Provides ideal substrates for heteroepitaxial growth of active device layers, essential for CMOS integration readiness. |
| Large-Area/High-Throughput Wafers | High-Quality PCD Wafers (up to 125 mm) | For scaling the design into complex systems or large arrays where cost and size are critical factors. |
| Advanced Power Electronics/Doping | Boron-Doped Diamond (BDD) | Customizable BDD layers available for conductive contacts, deep UV applications, or advanced material integration. |
Customization Potential
Section titled âCustomization PotentialâThe experimental setup requires highly specific device characteristics, often involving complex material stacks and geometries that 6CCVD routinely provides.
- Custom Dimensions and Substrates: 6CCVD offers SCD and PCD plates/wafers with custom dimensions up to 125 mm (PCD) and specialized thicknesses (0.1 ”m - 500 ”m), ensuring precise compatibility for unique foundry specifications or integration steps.
- Precision Surface Preparation: We offer advanced polishing achieving roughness Ra < 1 nm for SCD and < 5 nm for inch-size PCD. This ultra-smooth surface is mandatory for subsequent high-resolution lithography and active layer deposition required for OTA fabrication.
- Integrated Metalization Services: The reliable creation of ohmic contacts and gate structures for diamond transistors is critical for controlling transconductance (gm). 6CCVD provides in-house metalization using thin film stacks of Au, Pt, Pd, Ti, W, and Cu, tailored to specific contact needs for high-frequency operation.
- Substrates up to 10 mm Thickness: For high-power or high-rigidity applications, 6CCVD can supply supporting substrates up to 10 mm thick.
Engineering Support
Section titled âEngineering Supportâ6CCVDâs in-house team of PhD material scientists can assist engineers and researchers in transitioning from theoretical designs to robust physical implementation. We offer consultation on optimizing diamond material selection (SCD vs. PCD, doping profiles, surface termination) specifically for Reconfigurable Active Filter projects requiring high stability and operation at tens of MHz and beyond.
For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.
View Original Abstract
This paper deals with operational transconductance amplifiers (OTAs) -based active voltage-mode biquad filter with electronically reconfigurable transfer functions. Due to utilization of the very favourable active devices, this design is ready for immediate CMOS design. Presented filtering solution contains four active elements where each of them is directly used for reconnection-less change of transfer function or modification including electronic control of quality factor and tuning. The filter offers availability of all-pass, high-pass, band-pass, band-reject transfer response and special transfers as high-pass with zero and low-pass with zero. Measurement results based on utilization of diamond transistors confirmed expected behaviour of the circuit.