CS258978B1 - Low Noise Potentiometer - Google Patents

Abstract

A low-noise potentiometer without a sliding mechanical slider is designed. The potentiometer has two variable resistance parts. One is formed by a series connection of the first and second analog switches (Si, Sg), to whose common node (2) one electrode (6) of the first capacitor (C11) is connected. The second variable resistance part is formed by a series connection of the third and fourth analog switches (S1 and S4), to whose common node (4) one electrode (7) of the second capacitor (C2) is connected. The second electrode (8) of both capacitors (C, Cp) is common and is grounded. This second electrode (8) is movable relative to the first electrodes (6, 7) in a plane parallel to its surface. The potentiometer is usable wherever there are problems with noise arising from imperfect contact of the slider, with the stability of the resistance branches of the potentiometer or where there is a problem with the uniform connection of the potentiometer input terminals to each other, or of the input and output terminals, respectively.

Description

The invention relates to a low noise potentiometer which is designed without mechanical contact of the rider.

Potentiometers are used as widely used variable resistors and as resistive dividers with adjustable dividing ratio. The main problem of the current design of potentiometers is realization of the contact of the rider, sufficient mechanical resistance of the resistance layer surface against abrasion and its homogeneity. In a number of cases, the known noise effects accompanying the change of resistance by sliding the slider are also adversely affected.

These undesirable features of the prior art designs are eliminated by the low noise potentiometer formed by two variable resistive parts forming a resistive divider according to the invention. Its essence is that one variable resistor part consists of a series connection of the first and second analog switches, to whose common node is connected one electrode of the first capacitors. The second variable resistor branch consists of a series connection of the third and fourth analog switches, to whose common node one electrode of the second capacitor is connected. The second electrode of both capacitors is common and grounded. The second electrode is movable relative to the two first electrodes in a plane parallel to the surface of the first electrodes.

This potentiometer eliminates noise problems caused by imperfect rider contact. Another advantage of the solution according to the invention over known design solutions of potentiometers is the order of time and temperature stability of its parameters (resistance, dividing ratio). A great advantage of the proposed solution is also the possibility of numerical control of the values of the resistors forming the noise-free potentiometer of the present invention by changing the ratio of the switching frequencies of the frpi, frpg ^{in the} branches.

An example of a low noise potentiometer is shown in FIG.

Fig. 2 shows a detail of a pair of sliding capacitors with one common electrode.

One variable resistor part of the low noise potentiometer consists of a series of connected first and second switches S1, S2 between angles 1 and 2. One common electrode 6 of the first capacitor Οχ is connected to the common node 2 of these switches S1, S2. The second variable resistor part is formed analogously to the third and fourth switches S3 and S4, which are connected in series between the angles 2 and 0.

To their common node 4 is connected one electrode 7 of the second capacitor C2. This second electrode 8 is movable relative to the electrodes 6 and 7 in a direction parallel to their surface, in this example in the ordinate direction. The switches S1, S2, and S4 may be realized, for example, by means of transistors or transmission gates.

To suppress the residues of the switching frequencies lying high above the processed band, it is suppressed by connecting a low-pass filter 9 to the output of a low-noise potentiometer.

The low noise potentiometer works by:. the first and second switches Si and Sg alternately connect one electrode 6 of the first capacitor Οχ between terminals 1 and 2 · Similarly, the third and fourth switches alternately connect one electrode 7 of the second capacitor C2 between terminals 2 ^and 2 · ^{is the} system acting as a resistive divider?

The value of the variable resistive parts realized with switched capacitors ,χ, Cg is determined from the relation

Ri = ^f Ti Ci i = 1,2 / 1 / where ίχχ are switching frequencies of switches Sx, S2 resp. S4, S4

Ci is the capacity of the switched capacitor ^{of:> 0 7/0}

Cj resp. C2 in the first, respectively. the second variable resistor part.

It follows from the above relation A / that the magnitude of the resistances of the individual parts can be varied either by changing the switching frequency f £ nebo or by changing the capacitances of capacitors Ci, Cg.

The first and second capacitors Οχ and Cg have one terminal, terminal 0, in common. This is used so that the second electrode 6 of the capacitors C1, C2 and the dielectric are common. By moving the common second electrode 8 relative to the electrodes 6, 7, the capacities of capacitors C1, Cg are changed, and one of them increases and the other decreases.

The capacities of the two switched capacitors C1, Cg are given by the relation _sa

Cl = / 1 - x / / 2 /

C ₂ = ^x where je is the dielectric permittivity, a, 1, d are the parameters of the geometric arrangement of the electrodes

6, 7, 8 and x is the displacement of the common electrode 8 against the remaining electrodes 6, 7.

The voltage transfer of the unloaded low noise potentiometer is determined by the expression A / to / 5 /

Hi =

Hive

/ 4 /

From the expression (4) it is evident that the value of the voltage transfer Ug / Ui decreases with increasing x shift. When the electrode 8 is moved, there is no conductive contact between the plates and therefore no disturbing noise is present. Residual switching frequencies lying high above the processed band are suppressed by low-pass filter The electrode shapes 6, 7, 8 of the first and second capacitors Ci and Cg can be realized with respect to relation (4) other than linear functional dependence of voltage transfer.

- 4 logarithmic.

258 978

The connection of the noise-free potentiometer according to the invention can be advantageously used wherever needed, the application of hitherto known potentiometer solutions encountered problems with noise, resulting from imperfect contact of the rider, with time and temperature stability of the resistance branches of the potentiometer. DC connection of potentiometer input terminals through its resistance to each other, resp. input and output terminals.

Claims (1)

SUBJECT OF THE INVENTION Low noise potentiometer, consisting of two variable resistive parts forming a resistive divider, characterized in that one variable resistive part consists of a series connection of the first and second analog switches (Sp and Sg), to which a common electrode (2) is connected to a common node (2). 6) of the first capacitor (Cp) and the second variable resistive part is formed by the serial connection of the third and fourth analog switches (S5 and S4), to whose common node (4) one electrode (7) of the second capacitor (C2) is connected, (8) of the first and second capacitors (Cp and Cg) is common, is displaceable relative to the two first electrodes (6, 7) in a plane parallel to their surface and is grounded.