What Are Switched Capacitor Circuits? – A Beginner’s Guide

hqtFeb 9, 2020

Everything You Need to Know About Membrane Switch Overlay and Flexible Circuit

Switched Capacitor Circuits in China

Table of Contents:
1.Introduction to switched capacitor circuits, membrane switch overlay and flexible circuit
2. What has switched capacitor circuit?
3.The History of switched-capacitor circuits
4. Who made the first switch capacitor filter?
5.Use of switched capacitor circuit on domestic and commercial levels
6. What is a membrane switch overlay keyboard?
7.One- switched capacitor circuit 
8.Mechanism of switched capacitor circuits & membrane keyboard with integrated
9.How to ensure switched capacitor circuits quality?
10.Why switched capacitor circuits are a favorite choice for membrane keyboard manufacturers?
11.Switched capacitor circuits In a Nutshell



Do you know that switched capacitor circuits are extremely durable, resistant, dust and waterproof? These capacitors provide an option for users of customization. Subsequently, consumers can modify it according to their requirements.  Finally, being an expert membrane switch overlay manufacturer, I would like to share some of the best practices about:

  • Flexible circuit
  • Membrane switch overlay
  • Switched capacitor circuit

What is switched capacitor circuits?


China switched capacitor circuits

A switched capacitor circuit is a circuit composed of a switch and a capacitor controlled by a clock signal. In addition, it uses the storage and transfer of charges to implement various processing functions on signals. In actual circuits, sometimes a circuit comes with only switches and capacitors often does not meet the requirements.

Therefore, manufacturers combine it with amplifiers, operational amplifiers, comparators, etc. Likewise, to achieve the generation, transformation, and processing of electrical signals.

The History of switched-capacitor circuits

The use of switched capacitor circuits to process analog signals was first proposed in 1972. Furthermore, due to its special advantages, it has attracted people’s attention. And has strengthened research in this area. In 1977, a loop filter composed of NMOS technology and switched capacitor technology came on the horizon first time.

Who made the first switch capacitor filter?

In 1978, Intel Corporation of the United States first made a speech filter for a PCM telephone system and entered the practical stage.

Moreover, in recent years, research on the theory, analysis methods, and circuit technology of switched capacitors have been conducted in many aspects. Furthermore, switched capacitor circuits technology is expanding in the field of analog signal processing.

Use of switched capacitor circuits on domestic and commercial levels

Switched capacitor circuits have established themselves worldwide: outdoors as well as in industrial devices or in the household sector. Similarly, they impress with their great individual design freedom. Their longevity and their low installation depth. Likewise their construction takes up less than 1 mm of space.

It includes the complete circuit and even integrated key lighting. Simultaneously, it is no wonder that switched capacitor circuit are quite famous input systems in device construction.

What is a membrane switch overlay keyboard?

membrane switch overlay keyboard

Standard keyboard for personal computers!

One thing to pay attention to when preparing a membrane switch overlay is the type of keyboard. Further, we can divide it into two keyboards. Let’s check the structure and features of the membrane switched capacitor circuits that often share the same characteristics.

One- switched capacitor circuits  

However, in a broad sense, a pantograph and a buckling spring are included in the membrane switch overlay because a membrane sheet switch is used in it.

In addition, the membrane switch overlay keyboard is a favorite gadget for computers. But also, for game consoles such as Commodore Max Machine and Sinclair ZX80. Therefore, even today, computer users are becoming excited about choosing a keyboard.

Mechanism of switched capacitor circuits  & membrane keyboard with integrated switch

A typical example of a membrane keyboard is the rubber cup type. A rubber cap is a dome-shaped protrusion made of silicon. Subsequently, a rubber cap comes with a key cover of switched capacitor circuits.  By pressing the key, you can also deform it too.

Simultaneously, the protruding part of the deformed rubber cup contacts the contact part on the membrane sheet switch and the switch is pressed. Similarly, this type is widely used in personal computer keyboards and features a deep touch. In addition, the rubber cup type also has a thin membrane with a lighter touch than the normal one.

Membrane keyboard and mechanical keyboard


Membrane keyboard mechanical keyboard

Keyboards can be roughly classified into two types:

  1. mechanical keyboards
  2. membrane keyboards.

“The membrane keyboard has a single switch on the entire keyboard, while the mechanical keyboard has individual switches”

Switched capacitor circuits are widely used as standard keyboards in desktop and laptop computers. Because the integrated switch saves money over individual ones.

However, since the initial cost is low, it is an integrated switch. So, it is difficult to replace only the failed part if a failure occurs.

If there is a malfunction or trouble, the flexible circuit manufacturer should replace it.

A switched capacitor circuit consists of several individual layers.  Similarly, the flexible circuit manufacturer places it on the top. Subsequently, by default a switched capacitor flexible circuits consist of four basic parts:

  • Decorative film
  • upper and lower switching film and
  • a spacer film

A reputable membrane switch overlay and flexible circuit manufacturer van offer the services for the

  • development
  • design
  • production
  • service of quality switched capacitor circuits  

Custom made switched capacitor circuits  

Switched capacitor circuits with pressure points ensure reliable, low-bounce switching behavior, regardless of the type of key actuation. Therefore, the shape of the contact spring guarantees reliable contact with clear feedback.

How to ensure switched capacitor circuits quality?

The highest reliability requirements for practically de-energized circuits can be met by gold plating on both sides for rigid versions with printed circuit boards.

For country-specific labeling, switched capacitor circuits with insulated slide-in strips are ideal. Existing keyboards can be adapted to the respective labeling variant in no time at all. Of course, the service life is also right with well over 1 million switching cycles – guaranteed.

Why switched capacitor circuits are a favorite choice for membrane keyboard manufacturers?


switched capacitor circuit manufacturers

A flexible circuit membrane keyboard is as versatile as its areas of application and requires many years of experience in research, development, and production

  • adhesive selection tailored to the application
  • similarly, flexible circuits in silver technology and copper technology
  • integrated security chambers
  • Decorative films made of mechanically and chemically resistant polyester,
    which can also be supplied with antibacterial properties on request
  • Window areas printed or with panes, transparent or colored
  • selectively embossed buttons
  • finally, integrated SMD components, especially LEDs (displays) and resistors
  • targeted measures to improve the EMC properties

Switched capacitor circuits with conductor tracks in copper

For the demanding applications, membrane switch overlay can exclusively create a high-quality switched capacitor circuit. Similarly, it carries excellent properties of refined copper conductor tracks.

“These high-quality, copper-clad foils form the basis of this membrane keyboard.”

They have galvanically silver-plated or gold-plated characteristics for the most extreme areas of application. Therefore, the technology of the copper-clad switching level enables process-reliable SMD assembly of electronic components with a subsequent soldering process.

Subsequently, switched capacitor circuits manufacturer can reduce, or completely exclude with the gold-plated conductor tracks. Therefore, the CU conductor tracks offer the lowest loop resistance values ​​and minimized risk of the conductor tracks breaking.

You also have the advantages of PCB technology in the membrane switch overlay keyboard:

  • Soldering components instead of gluing
  • High resilience of copper tracks when deformed
  • No silver migration
  • Low electrical conductor resistance
  • High, reproducible layer thickness
  • High functional reliability and product reliability
  • Switched capacitor circuit of the highest quality and resilience –
  • In short, ideal for applications in medicine, computing technology

Switched capacitor circuits are benefiting following fields:


  • Automotive industry
  • measuring technology
  • Medical
  • Workshop Equipment
  • number systems

Similarly, the membrane switch overlay, the flexible circuit provides the following features:

  1. Clear tactile feedback
  2. Contact triggering is particularly easy
  3. Exceptionally good tactility of the keys
  4. Optimal pressure distribution
  5. Relief of the snap disc
  6. Freedom of design regarding the shape of the buttons


Particular advantages of switched capacitor circuits are:

  • Closed front surface
  • Dust and waterproof
  • Easy care and hygienic
  • Robust, scratch-resistant
  • Individual design printed on the back on foil
  • Ready for installation and connection
  • individual button sizes and arrangement
  • very good tactile feedback
  • Silicone Rubber Keypads

Above all, in many electronic devices, the switched capacitor circuit serves as the central component. It triggers a direct switching function on the flexible circuit board underneath and determines the haptic. The optical and tactile impression and electrical behavior via the integrated contact elements are also important.

Advantages of membrane switch overlay flexible circuit:

  • membrane switch overlay adapts to your design and is extremely flexible.
  • Different switched capacitor circuit colors, as well as multi-colored keyboard lights, provides easy implementation
  • Similarly, resistance to moisture, dirt, chemicals and thermal influences.
  • The actuation forces(force-displacement behavior) can be flexibly selected from 20g – 500g.
  • Key travelfrom 0.3 to 5.0 mm.
  • Variousswitched capacitor circuit implementation options for electrical contracting. From low-cost, carbon printing to high-quality metal contact pills with a current-carrying capacity of up to 2A. Furthermore, the use of metal snap disks or the actuation of a tact switch is also possible.
  • Thanks to special surface coatings, such as PU or epoxy coating, the keys are also permanently abrasion-resistant.
  • High-end flexible circuitkeyboards through switch mats with plastic or metal caps.  Therefore, the plastic caps provides design customization option in a variety of ways with different paintwork or chrome plating.
  • Long mechanical lifewith up to 10 million switching cycles.
  • Long-lasting solution with low maintenance risk.

Flexible circuit characteristics

  • Switched capacitor circuit for all applications
  • Easy to clean, free design
  • Dense front
  • Durable and tough


A switched capacitor circuits manufacturer can use all kinds of design ideas with membrane switch overlay. It provides a hassle-free configuration and component replacement.  With and without tactile feedback, rigid or flexible – depending on the application, the switched capacitor circuit can offer exactly the properties you want

FPC main raw materials

Its main raw materials are right:

  1. substrate
  2. cover film
  3. reinforcement
  4. other auxiliary materials.


1.1 Adhesive substrate

There are three main components of the glued substrate: copper foil, glue, and PI. There are two types of single-sided substrate and double-sided substrate. However, the material of only one side of the copper foil is a single-sided substrate, and the material of the two-sided copper foil is a Double-sided substrate.

1.2 Adhesive-free substrate

A non-adhesive substrate is a substrate without an adhesive layer. Compared with ordinary adhesive substrates, there is no intermediate adhesive layer. It consists of only two parts: copper foil and PI. Better dimensional stability, higher heat resistance, higher bending resistance, better chemical resistance, and other advantages, has now been widely used.

FPC type


pcb manufacturers china

There are 6 types of FPC types:
  1. Single panel:There is a line on only one side.
  2. Double panel:There are lines on both sides.
  3. Hollow plate:also known as window plate (finger window).

D, the layered board: two sides of the line (separated).

  1. Multi-layer boards:more than two layers of lines.
  2. Soft-hard board:A product combining soft and hard boards.


Switched capacitor circuits In a Nutshell

Flexible circuit (FPC) is a leading technology these days.  United States made it for the development of space rocket technology in the 1970s. It comes with polyester film or polyimide as a substrate with high reliability and excellent flexibility. The printed circuit comes in in a thin and light plastic sheet with circuit design. So that a large number of precision components have stacking option in a narrow and limited space to form a flexible circuit.

It is made of conductive circuit patterns by using light imaging pattern transfer and etching process methods on a flexible substrate surface. Moreover, the inner and outer layers of the double-sided and multilayer circuit boards are electrically connected through metalized holes. The surface of the circuit pattern has glu protection.

With the rapid development of the electronics industry, the circuit board design is becoming more and more accurate and denser. Traditional manual inspection methods have been unable to meet production needs. In addition, FPC defect automatic inspection has become an inevitable trend in industrial development.