A reconfigurable transition band butterworth-elliptic filter based on transistor switches

Abstract

The application discloses a reconfigurable transition Butterworth-elliptic filter based on transistor switches, which comprises a transition Butterworth-elliptic filter including a plurality of capacitors and inductors, the capacitors and the inductors are connected in a ladder shape, wherein the inductors are connected in series in a signal path, the capacitors are connected in parallel to the ground, and one capacitor is connected in parallel to both sides of the inductor at the end of the circuit; the capacitors connected in parallel to the ground in the transition Butterworth-elliptic filter are respectively provided with n first transistor switch-capacitor networks in parallel, and the capacitors connected in parallel to both sides of the inductor are provided with n second transistor switch-capacitor networks in parallel. The circuit structure of the transition Butterworth-elliptic filter is adopted, the frequency response has the characteristics of flatness in a passband and rapid roll-off in a transition band, and the values of the inductors and the capacitors are relatively small, thereby saving the chip area. The switch-capacitor network is introduced, the order is adjustable, the relatively small chip area and the relatively fast switching speed are realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of electronic circuit design, and in particular to a reconfigurable transition Butterworth-elliptic filter based on transistor switch. BACKGROUND

[0002] Radio frequency front end has been an indispensable part of modern wireless communication system, with the rapid development of current wireless communication technology and the large increase of wireless communication demand, new requirements for the function of radio frequency front end have been generated, and the design concept of reconfigurable radio frequency front end has emerged. The reconfigurable radio frequency front end refers to that the user can adjust the configurable parameters of some radio frequency devices in the radio frequency front end according to the use demand, and finally make the radio frequency front end show new technical indexes such as channel bandwidth, transmission power and the like. Compared with the traditional radio frequency front end, the reconfigurable radio frequency front end can show stronger applicability in the face of the current complex wireless communication environment.

[0003] The implementation of the reconfigurable radio frequency front end depends on the reconfigurable design of each radio frequency device composing it, among which the filter occupies a key position in the reconfigurable radio frequency front end. In order to make the radio frequency front end have reconfigurable function in channel selection, the reconfigurable design of the filter is essential. The usual way to realize the reconfigurable filter is to use variable reactance elements in the filter circuit, such as varactor diode, PIN diode switch-capacitor network, RF-MEMS switch-capacitor network and the like. In the actual application process, the frequency response of the filter is adjusted by adjusting the value of the variable reactance element, so as to achieve the purpose of the reconfigurable filter.

[0004] The main problem of the technology using varactor diode as variable reactance element is that it introduces loss and distortion in the circuit, and in addition, the adjustable order is limited by the used control signal; the main problem of the technology using PIN diode switch-capacitor network as variable reactance element is that it introduces loss and distortion in the circuit, and in addition, it needs to introduce RF choke to realize the switching characteristic of PIN diode, resulting in a large chip area; the problem of the technology using RF-MEMS switch-capacitor network as variable reactance element is slow switching speed. SUMMARY

[0005] Technical purpose: in view of the defects in the prior art, the present application discloses a reconfigurable transition Butterworth-elliptic filter based on transistor switch, which adopts switch and fixed capacitor to form switch-capacitor network, can freely design adjustable order, realizes relatively small chip area and relatively fast switching speed.

[0006] Technical scheme: in order to achieve the above technical purpose, the present application provides the following technical scheme.

[0007] The application discloses a reconfigurable transition Butterworth-elliptic filter based on transistor switches, which comprises a transition Butterworth-elliptic filter structure, a plurality of first transistor switch-capacitor networks and a plurality of second transistor-capacitor networks; the transition Butterworth-elliptic filter comprises a plurality of capacitors and inductors, the capacitors and inductors are connected in a ladder shape, wherein the inductors are connected in series in a signal path, the capacitors are connected in parallel to the ground, and one capacitor is connected in parallel on both sides of the inductor at the end of the circuit; the capacitors connected in parallel to the ground in the transition Butterworth-elliptic filter are respectively provided with n first transistor switch-capacitor networks in parallel, and the capacitors connected in parallel on both sides of the inductor are provided with n second transistor switch-capacitor networks in parallel; the first transistor switch-capacitor networks and the second transistor switch-capacitor networks are controlled by digital control signals generated by a decoder.

[0008] Preferably, the transition Butterworth-elliptic filter circuit structure comprises a plurality of capacitors and inductors, and the order is equal to the total number of the capacitors and inductors contained therein; the higher the order is, the better the performance is.

[0009] Preferably, the first transistor switch-capacitor network comprises a first inverter, a first transistor and a first capacitor, the input end of the first inverter is connected with a Yn signal, the output end of the first inverter is connected with the gate of the first transistor, the source of the first transistor is grounded, the drain of the first transistor is connected with one end of the first capacitor, and the other end of the first capacitor serves as an output end of the first transistor switch-capacitor network.

[0010] Preferably, the second transistor switch-capacitor network comprises a second inverter, a second transistor, a first second capacitor, a second second capacitor, a first second resistor and a second second resistor, the input end of the second inverter is connected with a Yn signal, the output end of the second inverter is connected with the gate of the second transistor, the input end of the second inverter is connected with the source of the second transistor through the first second resistor, the input end of the second inverter is connected with the drain of the second transistor through the second second resistor, the source of the second transistor is connected with one end of the second second capacitor, the other end of the second second capacitor serves as an input end of the second transistor switch-capacitor network, the drain of the second transistor is connected with one end of the first second capacitor, and the other end of the first second capacitor serves as an output end of the second transistor switch-capacitor network.

[0011] Preferably, in the first transistor switch-capacitor network and the second transistor switch-capacitor network, the transistor adopts a MOSFET field effect transistor.

[0012] Preferably, the same digital signal is used to control the n-path first transistor switch-capacitor network and the n-path second transistor switch-capacitor network. The digital signal is generated by a decoder and controls the first transistor switch-capacitor network and the second transistor switch-capacitor network. Finally, n+1 frequency responses of the transistor switch-based reconfigurable transition Butterworth-elliptic filter are controlled by the decoder.

[0013] Advantages: The present application uses the circuit structure of the transition Butterworth-elliptic filter, simultaneously realizes the frequency response characteristics of flat in the passband and fast roll-off in the transition band, and reduces the inductance and capacitance values used at the same frequency to realize a relatively small chip area. The electronic devices with switching characteristics are used as switches and fixed capacitors to form a switch-capacitor network, realize a reconfigurable frequency response, and freely design the reconfigurable order to realize a relatively small chip area and a relatively fast switching speed. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 is the circuit structure of the N-order transition Butterworth-elliptic filter in the present application;

[0015] Figure 2 is the circuit structure of the first transistor switch-capacitor network in the present application;

[0016] Figure 3 is the circuit structure of the second transistor switch-capacitor network in the present application;

[0017] Figure 4 is the final total circuit structure schematic diagram when the 5-order transition Butterworth-elliptic filter structure is used in the embodiment;

[0018] Figure 5 is Figure 4 the 5-order transition Butterworth-elliptic filter structure schematic diagram in the embodiment.

[0019] Figure 6 is Figure 4 the comparison of the frequency responses realized by the low-pass filter with a 3dB bandwidth of 3GHz and the frequency responses realized by the traditional Butterworth filter when the 5-order transition Butterworth-elliptic filter structure is used in the embodiment. DETAILED DESCRIPTION

[0020] In order to further illustrate the technical solutions disclosed in the present application, the following will be described in detail in combination with the drawings and embodiments in the specification. It should be understood by those skilled in the art that the preferred and improved solutions made without departing from the spirit of the present application fall within the protection scope of the present application, and the conventional techniques in the art are not described and explained in detail in the specific embodiments.

[0021] As shown in the drawingsFigures 1-3 As shown in the figure, a kind of reconfigurable transition Butterworth-elliptic filter based on transistor switch includes transition Butterworth-elliptic filter circuit structure, several first transistor switch-capacitor networks and several second transistor-capacitor networks;Transition Butterworth-elliptic filter includes several capacitors and inductors, capacitors and inductors are connected in a ladder-like manner, wherein inductors are connected in series in signal path, capacitors are connected in parallel to ground, and there is a capacitor connected in parallel to the inductors on both sides of the end of the circuit;The capacitors connected in parallel to ground in the transition Butterworth-elliptic filter are respectively provided with n (n is an integer, n≥1) first transistor switch-capacitor networks in parallel, and the capacitors connected in parallel to the inductors on both sides are provided with n (n is an integer, n≥1) second transistor switch-capacitor networks in parallel;The first transistor switch-capacitor network and the second transistor switch-capacitor network are controlled by the digital control signal Yn signal generated by the decoder.

[0022] The transition Butterworth-elliptic filter circuit structure includes several capacitors and inductors, and the order is equal to the total number of capacitors and inductors contained therein, and the higher the order, the better the performance. Its frequency response has the characteristics of flat passband and rapid roll-off in transition band.

[0023] As shown in the figure, Figure 2 As shown in the figure, the first transistor switch-capacitor network includes a first inverter, a first transistor and a first capacitor, the input end of the first inverter is connected with Yn signal, the output end of the first inverter is connected with the gate of the first transistor, the source of the first transistor is grounded, the drain of the first transistor is connected with one end of the first capacitor, and the other end of the first capacitor is used as the output end of the first transistor switch-capacitor network.

[0024] As shown in the figure, Figure 3 As shown in the figure, the second transistor switch-capacitor network includes a second inverter, a second transistor, a second capacitor, a second capacitor, a second resistor and a second resistor, the input end of the second inverter is connected with Yn signal, the output end of the second inverter is connected with the gate of the second transistor, the input end of the second inverter is connected with the source of the second transistor through the second resistor, the input end of the second inverter is connected with the drain of the second transistor through the second resistor, the source of the second transistor is connected with one end of the second capacitor, the other end of the second capacitor is used as the input end of the second transistor switch-capacitor network, the drain of the second transistor is connected with one end of the second capacitor, and the other end of the second capacitor is used as the output end of the second transistor switch-capacitor network.

[0025] The application adopts the circuit structure of the transition Butterworth-elliptic filter, simultaneously realizes the frequency response characteristics of flat in the passband and fast roll-off in the transition band, and realizes the relatively small chip area by reducing the inductance and capacitance values used at the same frequency, and simultaneously uses the electronic devices with switching characteristics as switches and fixed capacitors to form the switch-capacitor network, realizes the reconfigurable frequency response, the reconfigurable order can be freely designed, realizes the relatively small chip area and the relatively fast switching speed.

[0026] Embodiment:

[0027] The fifth-order transition Butterworth-elliptic filter is given in the embodiment, the first transistor switch-capacitor network and the second transistor-capacitor network are introduced on the basis of the fifth-order transition Butterworth-elliptic filter, and a reconfigurable transition Butterworth-elliptic filter based on the transistor switch is formed.

[0028] As shown in the accompanying Figure 4 A reconfigurable transition Butterworth-elliptic filter based on the transistor switch includes a fifth-order transition Butterworth-elliptic filter structure, a plurality of first transistor switch-capacitor networks and a plurality of second transistor-capacitor networks; the fifth-order transition Butterworth-elliptic filter structure includes a capacitor C2, a capacitor C4, a capacitor C5, an inductor L1 and an inductor L3, one end of the inductor L1 is used as the input end of the filter, the other end of the inductor L1 is connected with one end of the capacitor C2, one end of the capacitor C5 and one end of the inductor L3 respectively, the other end of the capacitor C2 is grounded, the other end of the capacitor C5 and the other end of the inductor L3 are short-circuited and then grounded through the capacitor C4, and the other end of the capacitor C5 and the other end of the inductor L3 are short-circuited and then used as the output end of the filter; the capacitor C2 and the capacitor C4 in the fifth-order transition Butterworth-elliptic filter structure are respectively provided with n first transistor switch-capacitor networks in parallel, and the capacitor C5 is provided with n second transistor switch-capacitor networks in parallel. The first transistor switch-capacitor networks and the second transistor switch-capacitor networks are controlled by the digital control signal Yn signal generated by the decoder. The order of the transition Butterworth-elliptic filter circuit is equal to the total number of the capacitors and the inductors contained therein, the higher the order is, the better the performance is, as shown in the accompanying Figure 5As shown, the 5th order transition Butterworth-elliptic filter circuit structure includes capacitor C2, capacitor C4, capacitor C5, inductor L1 and inductor L3. The normalized element values of capacitor C2, capacitor C4, capacitor C5, inductor L1 and inductor L3 under different design requirements are given in Table 1, Table 2 and Table 3, which give the normalized element values of transition Butterworth-elliptic filter under different stopband suppression conditions and different orders, the order of normalized element values listed in the table is the same as the connection order of inductors and capacitors in the circuit, wherein the first normalized element value is the normalized value of inductor, and the last normalized element value is the normalized value of capacitor connected in parallel on both sides of inductor, the actual values of elements in the transition Butterworth-elliptic filter can be calculated according to the normalized element values given in Table 1, Table 2 and Table 3 and the inverse normalization formula given in formula 1 and formula 2, wherein ω p represents the 3dB bandwidth of the transition Butterworth-elliptic filter, and R represents the characteristic impedance of the transition Butterworth-elliptic filter. k , C k , b k respectively represent the actual inductance value of the inductor used in the transition Butterworth-elliptic filter, the actual capacitance value of the capacitor used, and the normalized element value, and the formula calculation relationship is as follows:

[0029]

[0030]

[0031] The specific values of each element applied in the filter structure under different bandwidths can be inversely normalized according to formula 1 and formula 2. As shown in Table 1, Table 2 and Table 3, the normalized parameters of each element in the transition Butterworth-elliptic filter structure under three different design requirements are given. With the decrease of the out-of-band suppression, the values of each element in the transition Butterworth-elliptic filter decrease, the required chip area is reduced, and the transition Butterworth-elliptic filter has a steeper roll-off in the transition band. In the actual design process, appropriate normalized parameters should be selected according to the specific design requirements. Table 1 is the normalized element values of the transition Butterworth-elliptic filter with an out-of-band suppression greater than 20 dB in the present application; Table 2 is the normalized element values of the transition Butterworth-elliptic filter with an out-of-band suppression greater than 30 dB in the present application; Table 3 is the normalized element values of the transition Butterworth-elliptic filter with an out-of-band suppression greater than 40 dB in the present application. Tables 1-3 give the normalized element values of the 4th to 9th order transition Butterworth-elliptic filter. From top to bottom in the table, the normalized values of each element in the 4th, 5th, 6th, 7th, 8th and 9th order transition Butterworth-elliptic filter are represented, respectively. The third row is the normalized element values used in the 5th order transition Butterworth-elliptic filter in the present embodiment. The actual inductance values of the corresponding inductors and the actual capacitance values of the capacitors used in the 5th order transition Butterworth-elliptic filter can be calculated by combining formula 1 and formula 2.

[0032] Table 1

[0033]

[0034]

[0035] Table 2

[0036]

[0037] Table 3

[0038]

[0039] For example, the design index of a low-pass filter with a 3 dB bandwidth of 3 GHz is used to design the 5th order transition Butterworth-elliptic filter structure and the traditional Butterworth filter structure with ε = 1. The element values used are shown in Table 4. Table 4 is a comparison of the element values used for the design of a low-pass filter with a 3 dB bandwidth of 3 GHz using the 5th order transition Butterworth-elliptic filter structure and the element values used for the traditional Butterworth filter. The performance of the realized filter is shown in Table 5. Figure 6

[0040] Table 4

[0041] ​

[0042] As shown in Table 4, ε reflects the attenuation speed of the traditional Butterworth filter, and the greater the value, the faster the attenuation. Compared with the traditional Butterworth filter with ε = 1, the element value used by the transition Butterworth-elliptic filter is smaller, thereby reducing the chip area required for implementation. Especially when the out-of-band suppression is 20 dB, the element value used by the transition Butterworth-elliptic filter is reduced by 29.28% compared with the traditional Butterworth filter with ε = 1. As shown in Figure 6 The frequency response of the transition Butterworth-elliptic filter in the passband is similar to that of the traditional Butterworth filter, and both are very flat. However, the Butterworth-elliptic filter has a steeper roll-off in the transition band, which is similar to the frequency response of the elliptic filter. In summary, the properties of the transition Butterworth-elliptic filter are between those of the Butterworth filter and the elliptic filter, so it is called the transition Butterworth-elliptic filter.

[0043] In the first transistor switch-capacitor network and the second transistor switch-capacitor network of the application, the transistor is implemented by using an electronic device with switching characteristics, such as MOSFET; in addition, the same digital signal is used to control the n-way first transistor switch-capacitor network and the n-way second transistor switch-capacitor network, that is, the Yn signal is the same digital signal in the first transistor switch-capacitor network and the second transistor switch-capacitor network, and the number of control signals is reduced from n to m = log2n by using a decoder, thereby making the reconfigurable control more concise; by controlling the Yn signal, the application uses an electronic device with switching characteristics, such as MOSFET field effect transistor, as a switch and fixed capacitor to form a switch-capacitor network, which can be freely designed to have adjustable order, thereby achieving relatively small chip area and relatively fast switching speed.

[0044] The filter structure in the application adopts a transition Butterworth-elliptic filter structure, which can reduce the values of inductors and capacitors used, thereby reducing the chip area; the filter of the application can finally achieve a frequency response with flat passband and fast roll-off in the transition band, and a transistor switch-capacitor network is used to replace the fixed capacitor in the original filter circuit to realize reconfigurable design, as shown in Figure 4 Each network is composed of one fixed capacitor and n switch-capacitors, and the network can have n+1 kinds of capacitance values by controlling the on-off of the switch, thereby making the designed filter have n+1 kinds of reconfigurable frequency responses. In the application, the n+1 kinds of capacitance values correspond to n+1 order adjustable filters, each Yn signal controls the conduction and shutdown of each switch-capacitor path, and the n switch-capacitor paths are controlled by Y1, Y2, …, Yn respectively, wherein each signal is a 0, 1 digital signal.

[0045] The above merely describes the preferred embodiments of the present application, and it should be pointed out that those skilled in the art can make several improvements and refinements without departing from the principles of the present application, and these improvements and refinements should also be considered as falling within the protection scope of the present application.

Claims

1. A transistor switch based reconfigurable transition Butterworth-elliptic filter characterized by: The transition Butterworth-elliptic filter circuit structure includes a plurality of capacitors and inductors, the capacitors and inductors are connected in a ladder shape, wherein the inductors are connected in series in a signal path, the capacitors are connected in parallel to the ground, and there is a capacitor connected in parallel to both sides of the inductor at the end of the circuit; the capacitors connected in parallel to the ground in the transition Butterworth-elliptic filter are respectively connected in parallel with n first transistor switch-capacitor networks, and the capacitors connected in parallel to both sides of the inductor are connected in parallel with n second transistor switch-capacitor networks; the first transistor switch-capacitor networks and the second transistor switch-capacitor networks are controlled by a digital control signal Yn signal generated by a decoder.

2. The reconfigurable transition Butterworth-elliptic filter based on transistor switches according to claim 1, characterized in that: The transition Butterworth-elliptic filter circuit structure includes a plurality of capacitors and inductors, the number of orders is equal to the total number of capacitors and inductors contained therein.

3. The reconfigurable transition Butterworth-elliptic filter based on transistor switches according to claim 1, characterized in that: The first transistor switch-capacitor network includes a first inverter, a first transistor and a first capacitor, the input end of the first inverter is connected with the Yn signal, the output end of the first inverter is connected with the gate of the first transistor, the source of the first transistor is grounded, the drain of the first transistor is connected with one end of the first capacitor, and the other end of the first capacitor serves as the output end of the first transistor switch-capacitor network.

4. The reconfigurable transition Butterworth-elliptic filter based on transistor switches according to claim 1, characterized in that: The second transistor switch-capacitor network includes a second inverter, a second transistor, a second first capacitor, a second second capacitor, a second first resistor and a second second resistor, the input end of the second inverter is connected with the Yn signal, the output end of the second inverter is connected with the gate of the second transistor, the input end of the second inverter is connected with the source of the second transistor through the second first resistor, the input end of the second inverter is connected with the drain of the second transistor through the second second resistor, the source of the second transistor is connected with one end of the second second capacitor, the other end of the second second capacitor serves as the input end of the second transistor switch-capacitor network, the drain of the second transistor is connected with one end of the second first capacitor, and the other end of the second first capacitor serves as the output end of the second transistor switch-capacitor network.

5. The reconfigurable transition Butterworth-elliptic filter based on transistor switches according to claim 1, characterized in that: In the first transistor switch-capacitor network and the second transistor switch-capacitor network, the transistor is a MOSFET field effect transistor.

6. The reconfigurable transition Butterworth-elliptic filter based on transistor switches according to claim 1, characterized in that: The same digital signal is used to control n first transistor switch-capacitor networks and n second transistor switch-capacitor networks, the digital signal is generated by a decoder and controls the first transistor switch-capacitor network and the second transistor switch-capacitor network, and finally n+1 kinds of frequency responses of the transistor switch-based reconfigurable transition Butterworth-elliptic filter are controlled by the decoder.

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