MCP601T-I/OT 6 Channel Sallen Key High Pass Filter Reference Schematic Design

The MCP601T-I/OT is a low-power, rail-to-rail output operational amplifier designed by Microchip Technology. It is a cornerstone for precision signal conditioning in battery-powered and industrial environments, operating with a single supply voltage as low as 2.7V. In this reference schematic, the IC is utilized as the active element in a 6-channel Sallen-Key high-pass filter array. This topology is primarily used to remove DC offsets, low-frequency rumble, or 50/60 Hz mains interference from sensitive sensor data while providing a robust, low-impedance output for downstream digitization.

Overview of the MCP601T-I/OT

As a CMOS-based amplifier, the MCP601 provides extremely low input bias currents, which is essential for active filter designs using high-value resistors. Its 2.8 MHz Gain Bandwidth Product (GBWP) allows it to handle audio-band and low-frequency ultrasonic signals with high fidelity. The device is particularly suited for applications such as automotive sensor interfaces, portable medical instrumentation, and industrial process control where space and power efficiency are primary constraints.

Technical Specification	Value
Supply Voltage Range	2.7V to 6.0V
Gain Bandwidth Product	2.8 MHz
Slew Rate	2.3 V/us
Quiescent Current	230 uA (typical)
Input Offset Voltage	2 mV (maximum)
Output Type	Rail-to-Rail
Phase Margin	50 degrees
Package	5-lead SOT-23

Pin Configuration and Function Mapping

The MCP601T-I/OT is housed in a compact SOT-23 package, allowing for dense multi-channel filter implementations.

Pin Number	Primary Function	Secondary / Peripheral Functions
1	VOUT	Amplifier Output / Feedback Node
2	VSS	Negative Supply / Ground Reference
3	VIN+	Non-inverting Input (Filter Input)
4	VIN-	Inverting Input (Unity Gain Feedback)
5	VDD	Positive Supply (5V)

Functional Block Analysis & Design Decisions

Signal Conditioning: 2nd Order Active Sallen-Key Filter

The primary functional block in this schematic is a 2nd order active Sallen-Key high-pass filter. This topology is selected for its non-inverting nature and high input impedance, which prevents the filter from loading the signal source. Each channel is tuned to a Q-factor of 0.707, achieving a Butterworth response. This response is critical for engineering applications requiring a maximally flat passband, ensuring that the signals of interest are not distorted by peaking before the roll-off occurs.

Technical Deep-Dive: Frequency Scaling and BOM Standardization

The design covers a wide frequency spectrum from 100 Hz to 10 MHz across six independent channels. To optimize the Bill of Materials (BOM), the resistance values (R1-R12) are standardized at 10 kOhms. Senior engineers will recognize that keeping resistance values constant while scaling capacitors simplifies procurement and assembly without sacrificing performance. The 10 kOhm value is low enough to keep thermal noise floors minimal while remaining high enough to stay well within the drive capabilities of most analog sensors.

Component Selection: Stability and Dielectrics

The selection of capacitors is frequency-dependent. For lower frequency channels (100 Hz to 10 kHz), ceramic X7R capacitors are used for their high volumetric efficiency. However, for the high-frequency channels (100 kHz to 10 MHz), C0G (NP0) dielectrics are mandatory. C0G capacitors provide a near-zero temperature coefficient and negligible voltage coefficient, ensuring the filter pole does not shift as the signal amplitude or ambient temperature fluctuates.

Placement and Trace Logic

Physical layout for high-pass filters requires the series capacitors (C1, C2, etc.) to be placed as close to the IC input pins as possible. This minimizes the trace area of the sensitive high-impedance node, reducing susceptibility to electromagnetic interference (EMI). A solid ground plane is essential for the shunt resistors (R3, R4, etc.) to provide a low-impedance return path, preventing ground-loop noise from modulating the filter’s baseline.

Design Rationale: DC Blocking and Pole Definition

The series capacitors serve a dual purpose: they define the filter poles and act as high-quality DC blocks. In high-pass applications, this prevents DC offsets from the input source from saturating the amplifier rails. The 10 kOhm resistors are used to define the return path for the op-amp’s input bias current, ensuring the non-inverting input does not float—a common design requirement for CMOS amplifiers.

Implementation Insights

When integrating the MCP601T-I/OT into a larger system, the Gain Bandwidth Product (GBWP) remains the primary constraint. While the schematic includes a 10 MHz channel (U6), the 2.8 MHz GBWP of the MCP601 means that the active filtering performance will degrade significantly at this frequency. At 10 MHz, the op-amp acts more as a low-impedance buffer than a precise active filter stage. For applications requiring sharp active roll-offs above 1 MHz, a higher-speed amplifier would be necessary.

Grounding for the 8-channel array should follow a star-grounding strategy. Digital noise from nearby microcontrollers can couple into the high-impedance feedback loops of the Sallen-Key topology. It is advisable to keep analog signal traces on a separate layer or isolated by ground pours to maintain the 108 dB dynamic range potential of the signal chain.

Although not explicitly shown in every sub-block, 0.1 uF ceramic decoupling capacitors must be placed within 2 mm of the VDD pin (Pin 5) for every IC. High-frequency noise on the power rail can bypass the common-mode rejection of the amplifier, appearing as noise in the passband.

Applications

• Sensor Baseline Restoration: Removing slow-moving DC drift and 50/60 Hz hum from industrial pressure and temperature sensors.
• Audio Signal Processing: Eliminating sub-sonic rumble and DC offsets in microphone pre-amplifiers and line-level interfaces.
• Medical Diagnostic Equipment: Removing large DC offsets from biopotential electrodes (ECG/EEG) while preserving high-frequency biological data.
• Vibration Analysis: Filtering out low-frequency mechanical noise in accelerometer-based condition monitoring systems.

Integrating the MCP601T-I/OT into your design

The 09-013 6-Channel Sallen Key High Pass Filter block provides a production-ready, modular solution for multi-decade frequency management. By utilizing the MCP601’s rail-to-rail capabilities and standardized 10 kOhm resistor networks, this block eliminates the repetitive iterative calculations usually required for high-order filter design. It offers a stable, low-impedance output that is ready to interface with any modern high-speed data acquisition system.

Skip the tedious research and manual entry. Download the production-ready schematic block for the MCP601T-I/OT directly from the Quickboards Library.