CN104410383A - High-order simulation N-channel active band-pass filter with tunable frequency - Google Patents
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Abstract
The invention discloses a high-order simulation N-channel active band-pass filter with tunable frequency. The filter comprises an active band-pass filter body, wherein the active band-pass filter body comprises M N-channel filter groups, 2*(M-1) gyrators and a clock generator. Two single-end active filters are combined to form a complete differential double-end N-channel active band-pass filter, and even harmonics are eliminated; each gyrator comprises an operational transconductance amplifier based on a phase inverter, and can increase the gain of the filters effectively; and the clock generator is used for supplying periodic sampling pulse sequence to the N-channel active filter, so that the center frequency of the filter is only determined by the clock frequency. According to simulation of a 6-order 8-channel active band-pass filter, a simulation result shows that the variable range is 0.2 G-2.0 G, so that the band-pass filter has bandwidth tunable center frequency, besides, the band-pass filter has the characteristics of good stability and low sensitivity and has wide application in the field of communication systems.
Description
Technical Field
The invention relates to an analog filter, in particular to a high-order analog N-channel frequency-adjustable active band-pass filter.
Background
In a wireless communication system, a band-pass filter applied to a wireless receiver is required to have good selectivity and a wide dynamic rangeAnd a freely adjustable center frequency. At present, a high-Q band-pass filter is usually constructed by using an N-channel filtering unit, and the Q value can be as high as 10 by properly selecting parameters such as center frequency, channel number and the like in a circuit4Of the order of magnitude. The N-channel filtering unit can realize comb filtering, good narrow-band filtering characteristics can be easily obtained, capacitive baseband impedance in the N-channel filtering unit can simulate an RLC network, and the center frequency of the capacitive baseband impedance can be adjusted by changing the frequency of a sampling pulse sequence generated by a clock generator. Due to the repeatability of sampling and the noise suppression effect of the integrator, the signal-to-noise ratio of the N-channel filtering unit is greatly improved compared with that of a traditional filter, and the N-channel filtering unit has the advantages of good stability and low sensitivity.
However, the conventional bandpass filter belongs to a passive bandpass filter, and the internal conventional N-channel filtering unit is composed of N channels and a sampling pulse generating circuit, and each channel has the same transfer function H (j ω). When the conventional passive RC structure H (j ω) is applied to the N-channel filter unit, a narrow bandwidth can be obtained, but the conventional passive RC structure H (j ω) occupies a large chip area and has a small dynamic range.
Disclosure of Invention
The invention aims to solve the technical problems that a traditional N-channel filtering unit has the defects of small dynamic range and large volume in the process of forming an N-channel band-pass filter, and provides a high-order analog N-channel frequency-adjustable active band-pass filter.
In order to solve the problems, the invention is realized by the following technical scheme:
a high-order analog N-channel frequency-tunable active band-pass filter comprises an active band-pass filter body. The active band-pass filter body is composed of M N-channel filtering groups, 2(M-1) gyrators and 1 clock generator, wherein N is a positive even number larger than or equal to 2, and M is an odd number larger than or equal to 3. The clock generator includes N D flip-flops. The high level and the low level of the clock end of each D flip-flop are respectively connected with the outsideThe high level and the low level of the partial clock are connected. The Q end of the previous D trigger is connected with the D end of the next D trigger, and the D end of the first D trigger is connected with the Q end of the last D trigger. The S terminal of each D flip-flop outputs a sequence of sampling pulses. The N-channel filtering group comprises N switch branches anda capacitor. Each switch branch is composed of 2 switches connected in series. Two ends of each capacitor are respectively bridged on the 2 switch branches, and two ends of each capacitor are connected to the common end connected with the 2 switches, namely, the 2 switch branches and the 1 capacitor form an H-shaped circuit structure, and the number of the H-shaped circuit structure is the same as that of the capacitors. The switch at the upper left position and the switch at the lower right position in each H-shaped circuit structure are simultaneously connected with the S end of one D trigger, namely, connected with the same sampling pulse sequence, and the switch at the lower left position and the switch at the upper right position in each H-shaped circuit structure are simultaneously connected with the S end of the other D trigger, namely, connected with the other same sampling pulse sequence. Every two N-channel filtering groups are connected through 2 gyrators, two ends of the former N-channel filtering group are connected with input ends of the 2 gyrators, and two ends of the latter N-channel filtering group are connected with output ends of the 2 gyrators. The ports of the first N-channel filtering group connected with the input ends of the 2 gyrators form the positive electrode and the negative electrode of the input end of the active band-pass filter body, and the ports of the last N-channel filtering group connected with the output ends of the last 2 gyrators form the positive electrode and the negative electrode of the output end of the active band-pass filter body.
In the above scheme, when each N-channel filtering group is connected to the clock generator, the switch at the upper left position in the ith H-shaped circuit structure is connected to the S-terminal of the ith D flip-flop, and the switch at the upper right position in the ith H-shaped circuit structure is connected to the ith D flip-flopThe S ends of the D flip-flops are connected, wherein
In the above scheme, the switch is a metal oxide semiconductor transistor.
In the above scheme, the gyrator is a transconductance amplifier based on an inverter.
In the above scheme, the phase difference between the positive electrode and the negative electrode of the input end of the active band-pass filter body is 180 °.
In the scheme, the value range of N is between 2 and 16, and the value range of M is between 3 and 9.
Compared with the prior art, the invention combines two paths of single-ended active filters into a complete differential double-ended N-channel active band-pass filter, thereby eliminating even harmonics; the gyrator is composed of a transconductance operational amplifier based on an inverter, and can effectively increase the gain of the filter; the clock generator is used for providing a periodic sampling pulse sequence for the N-channel active filter, so that the center frequency of the filter is only determined by the clock frequency; by simulating the 6-order 8-channel active band-pass filter, the simulation result shows that the variable range is 0.2G to 2.0G, so that the active band-pass filter has the characteristics of wide and adjustable center frequency, good stability and low sensitivity, and is widely applied to the field of communication systems.
Drawings
Fig. 1 is a schematic circuit diagram of an N-channel filter bank and a gyrator of a high-order analog N-channel frequency tunable active band-pass filter.
Fig. 2 is a schematic circuit diagram of a clock generator for a high-order analog N-channel frequency tunable active bandpass filter.
Fig. 3 is a schematic circuit diagram of a gyrator in fig. 1.
Fig. 4 is a schematic circuit diagram of a D flip-flop of fig. 2.
Fig. 5 is a frequency characteristic curve of a high-order analog N-channel frequency tunable active band-pass filter (6 th order 8 channel).
Detailed Description
The invention designs a high-order analog N-channel frequency-adjustable active band-pass filter, which comprises an active band-pass filter body as shown in figure 1. The active band-pass filter body is composed of M N-channel filtering groups, 2(M-1) gyrators and 1 clock generator, wherein N is a positive even number larger than or equal to 2, and M is an odd number larger than or equal to 3. In the preferred embodiment of the invention, the active band-pass filter body is a 6-order 8-channel active band-pass filter composed of 3N-channel filter groups, 4 gyrators and 1 clock generator.
The clock generator is shown in fig. 2 and comprises N D flip-flops. The high level and the low level of the clock end of each D flip-flop are respectively connected with the high level and the low level of an external clock. The Q end of the previous D trigger is connected with the D end of the next D trigger, and the D end of the first D trigger is connected with the Q end of the last D trigger. The S terminal of each D flip-flop outputs a sequence of sampling pulses. The structure of each D flip-flop is shown in fig. 4, and each D flip-flop is composed of two CMOS inverters and two CMOS transmission gates. The external clock CLK controls the CMOS transmission gate to turn on and off.
The gyrator is constructed with a transconductance operational amplifier based on an inverter, having no internal nodes, and having good linearity. The transconductance operational amplifier is composed of an nmos transistor and a pmos transistor, see fig. 3. In the preferred embodiment of the present invention, all 2(M-1) gyrators are identical in construction. In order to obtain the required filter gain, the transconductance of the transconductance operational amplifier can be changed according to the requirement, and 2 filters connected in the same N-channel filtering groupThe transconductances of gyrators, i.e., transconductance operational amplifiers, are the same (i.e., g)m1And gm1'transconductance of' is the same, gm2And gm2' the transconductance is the same); the transconductances of the gyrators, i.e., transconductance operational amplifiers, connected to different N-channel filter groups may be the same (g)m1And gm2The same transconductance) or different (g)m1And gm2Are not the same). In the preferred embodiment of the present invention, two transconductance operational amplifiers, gm1And gm1' the transconductance is 60ms, gm2And gm2' has a transconductance of 24 ms.
The N-channel filtering group comprises N switch branches anda capacitor. Each switch branch is composed of 2 switches connected in series. In the preferred embodiment of the present invention, each switch is implemented by an N-type metal oxide semiconductor transistor (NMOS), and a switch on-resistance of less than 10 Ω can be obtained for NMOS transistors with a width-to-length ratio of 800 or more. Two ends of each capacitor are respectively bridged on the 2 switch branches, and two ends of each capacitor are connected to the common end connected with the 2 switches, namely, the 2 switch branches and the 1 capacitor form an H-shaped circuit structure, and the number of the H-shaped circuit structure is the same as that of the capacitors.
The switch at the upper left position and the switch at the lower right position in each H-shaped circuit structure are simultaneously connected with the S end of one D trigger, namely, connected with the same sampling pulse sequence, and the switch at the lower left position and the switch at the upper right position in each H-shaped circuit structure are simultaneously connected with the S end of the other D trigger, namely, connected with the other same sampling pulse sequence. Specifically, when each N-channel filter group is connected to the clock generator, the switch at the upper left position in the ith H-shaped circuit structure is connected to the S-terminal of the ith D flip-flop, and the switch at the upper right position in the ith H-shaped circuit structure is connected to the ith D flip-flopThe S ends of the D flip-flops are connected, wherein
Every two N-channel filtering groups are connected through 2 gyrators, two ends of the former N-channel filtering group are connected with input ends of the 2 gyrators, and two ends of the latter N-channel filtering group are connected with output ends of the 2 gyrators. The ports of the first N-channel filtering group connected with the input ends of the 2 gyrators form the positive electrode and the negative electrode of the input end of the active band-pass filter body, and the ports of the last N-channel filtering group connected with the output ends of the last 2 gyrators form the positive electrode and the negative electrode of the output end of the active band-pass filter body.
The performance of the present invention will be further described in detail below by taking a 6 th-order 8-channel active band-pass filter composed of 3 8-channel filter groups, 1 clock generator and 4 gyrators as an example:
according to the 6 th-order 8-channel active band-pass filter of the embodiment, as shown in fig. 1, after an input signal passes through an 8-channel switched capacitor network, the output of the band-pass filter presents characteristics of high-Q band-pass, good stability, low sensitivity and the like, and the central frequency of the active filter can be adjusted by changing the frequency of a sampling pulse sequence of a clock generator.
By utilizing the repeatability of periodic signals, N switched capacitor networks are used for sampling and integrating the input signals in sequence in each period, and the transmission function of the output voltage of the N-channel filter bank is
In the formula, ω0The sampling frequency of each channel transfer function is N omega for the central frequency of the filter0；
The pass band width is:
thus the bandwidth is associated with N and CBBIn inverse proportion. The quality factor is:
thus the quality factor is associated with N and CBBIn direct proportion, the more channels are, the more the capacitor CBBThe larger the quality factor Q of the filter, the better the frequency-selective characteristic of the filter.
The system frequency response generated by N-channel filtering presents a comb-shaped band-pass characteristic and a step wave form, namely, on the whole frequency domain, an infinite number of pass bands exist, the center frequencies of the pass bands are respectively 0 and f0,kf0(k ═ 1, ± 2 …), except that k ═ mN, m is a natural number. The input useful signal waveform can be recovered by adding a common band-pass filter at the output end.
The 8 sampling pulse sequences used by the 6-step 8-channel active band-pass filter are generated by 8-phase clock generators which do not overlap with each other. Fig. 2 shows a non-overlapping 8-phase clock generator, which is composed of 8D flip-flops with good phase matching, the D flip-flops divide an external clock whose frequency is 8 times of a switching frequency into 8 parts, and then generate 8 clock output signals with a duty ratio of 12.5%, i.e. sampling pulse sequences, and the 8 sampling pulse sequences periodically sample and integrate the input signals in sequence, so that the low-pass filtering characteristic of a single channel presents a comb-shaped band-pass characteristic in the whole system. The use of a transmission gate in each D flip-flop, as shown in fig. 4, can achieve the advantages of low power consumption and high speed.
The gyrator is composed of a transconductance amplifier g based on an inverterm1And gm2The MOS tube in the phase inverter adopts the minimum channel length of the process; this type of transconductance amplifier achieves very low second order harmonic distortion, which will compensate for the second order harmonic distortion due to circuit mismatch.
According to the basic principle of the general N-channel filter, the low-pass transfer function of the single-ended active filter is obtained by analyzing and calculating:
wherein,
(wherein, go1,go2Are transconductance operational amplifiers gm respectively1,gm2Output admittance of RSFor input matching of resistors, CBB1,CBB2,CBB3Is a baseband capacitor)
By converting H(s) to the clock frequency floThe final bandpass transfer function is obtained, namely:
Htotal(j(ωlo+Δω))＝sinc2(pi/N). times.H (j (Δ ω)) (where N is the number of channels)
The switch in the switch capacitor branch of the 6-order 8-channel active band-pass filter is realized by an N-type metal oxide semiconductor transistor (NMOS), so that the on-resistance of the switch and the noise of the filter can be reduced, and the linearity can be improved. The NMOS transistor with the width-length ratio of more than 800 can obtain the switch on resistance lower than 10 omega. However, the aspect ratio of the NMOS transistor may not be too large, which may introduce additional parasitic capacitance and may increase dynamic power consumption.
When the single-ended input signal is used, the single-ended input signal is converted into differential signals with the phase difference of 180 degrees through the balance-unbalance converter, the differential signals respectively flow through the two branches, and even-number subharmonics are eliminated after the differential signals pass through the 6-order 8-channel active band-pass filter. By changing the clock frequency, the center frequency of the active band-pass filter changes accordingly. The 6 th-order 8-channel active band-pass filter is simulated, and the adjustable range of the frequency is 0.2G to 2.0G, see FIG. 5.
The high-order simulation N-channel frequency-adjustable active band-pass filter designed by the invention can be applied to the detection of weak signals in modern test instruments. To increase the order of the filter, the design method is applied, and the switched capacitor network and the gyrator are added behind the filter, so that a higher-order N-channel active band-pass filter with better performance can be realized.
Claims (6)
1. High-order simulation N passageway adjustable active band pass filter of frequency, including the active band pass filter body, its characterized in that: the active band-pass filter body consists of M N-channel filtering groups, 2(M-1) gyrators and 1 clock generator, wherein N is a positive even number which is more than or equal to 2, and M is an odd number which is more than or equal to 3;
the clock generator comprises N D triggers; the high level and the low level of the clock end of each D trigger are respectively connected with the high level and the low level of an external clock; the Q end of the previous D trigger is connected with the D end of the next D trigger, and the D end of the first D trigger is connected with the Q end of the last D trigger; the S end of each D trigger outputs a sampling pulse sequence;
the N-channel filtering group comprises N switch branches anda capacitor; each switch branch is composed of 2 switches connected in series; two ends of each capacitor are respectively bridged on the 2 switch branches, and two ends of each capacitor are connected to the common end connected with the 2 switches, namely the 2 switch branches and the 1 capacitor form an H-shaped circuit structure, and the number of the H-shaped circuit structure is the same as that of the capacitors; the switch at the upper left position and the switch at the lower right position in each H-shaped circuit structure are simultaneously connected with the S end of one D trigger, and the switch at the lower left position and the switch at the upper right position in each H-shaped circuit structure are simultaneously connected with the S end of the other D trigger;
every two N-channel filtering groups are connected through 2 gyrators, two ends of the former N-channel filtering group are connected with input ends of the 2 gyrators, and two ends of the latter N-channel filtering group are connected with output ends of the 2 gyrators; the ports of the first N-channel filtering group connected with the input ends of the 2 gyrators form the positive electrode and the negative electrode of the input end of the active band-pass filter body, and the ports of the last N-channel filtering group connected with the output ends of the last 2 gyrators form the positive electrode and the negative electrode of the output end of the active band-pass filter body.
2. The high-order analog N-channel frequency tunable active bandpass filter of claim 1, wherein: when each N-channel filtering group is connected with the clock generator, the switch at the upper left position in the ith H-shaped circuit structure is connected with the S end of the ith D trigger, and the switch at the upper right position in the ith H-shaped circuit structure is connected with the ith D triggerThe S ends of the D flip-flops are connected, wherein
3. The high-order analog N-channel frequency tunable active bandpass filter of claim 1, wherein: the switch is a metal oxide semiconductor transistor.
4. The high-order analog N-channel frequency tunable active bandpass filter of claim 1, wherein: the gyrator is an inverter-based transconductance amplifier.
5. The high-order analog N-channel frequency tunable active bandpass filter of claim 1, wherein: the phase difference between the positive pole and the negative pole of the input end of the active band-pass filter body is 180 degrees.
6. The high-order analog N-channel frequency tunable active bandpass filter of claim 1, wherein: the value range of N is between 2 and 16, and the value range of M is between 3 and 9.
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104953981A (en) * | 2015-07-15 | 2015-09-30 | 广西师范大学 | Gain enhancement type N-channel active band-pass filter adopting differential clock |
| CN108134590A (en) * | 2017-12-20 | 2018-06-08 | 广西师范大学 | A kind of N channel wave filter |
| CN108702144A (en) * | 2016-01-21 | 2018-10-23 | 高通股份有限公司 | Height inhibits the band logical N channel filter in broadband |
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| US5724000A (en) * | 1995-10-20 | 1998-03-03 | U.S. Philips Corporation | Differential switched capacitor filtering |
| CN204316465U (en) * | 2014-12-18 | 2015-05-06 | 广西师范大学 | High-order simulation N channel frequency-adjustable active band-pass filter |
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2014
- 2014-12-18 CN CN201410795472.0A patent/CN104410383A/en active Pending
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| Publication number | Priority date | Publication date | Assignee | Title |
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| US5724000A (en) * | 1995-10-20 | 1998-03-03 | U.S. Philips Corporation | Differential switched capacitor filtering |
| CN204316465U (en) * | 2014-12-18 | 2015-05-06 | 广西师范大学 | High-order simulation N channel frequency-adjustable active band-pass filter |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN104953981A (en) * | 2015-07-15 | 2015-09-30 | 广西师范大学 | Gain enhancement type N-channel active band-pass filter adopting differential clock |
| CN108702144A (en) * | 2016-01-21 | 2018-10-23 | 高通股份有限公司 | Height inhibits the band logical N channel filter in broadband |
| CN108134590A (en) * | 2017-12-20 | 2018-06-08 | 广西师范大学 | A kind of N channel wave filter |
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Application publication date: 20150311 |