CN204517770U - Multi-mode configurable filter - Google Patents

Abstract

The utility model discloses a kind of multi-mode configurable filter, it is made up of analog center, digital control center and reference voltage current source, analog center leads to multiplex filter, hysteresis comparator, input stage and output stage by lower passband and forms, and digital control center is made up of SPI, clock module, logic control element, sampling clock selected cell, counter and memory register.A kind of multi-mode configurable filter that the utility model provides, digital control center is adopted to be configured filter mode, filter can be made to be operated in the logical and adaptive model of bypass mode, low pass, band, hysteresis comparator and memory register is adopted to improve antijamming capability, functional.

Description

Multimode Configurable Filters

technical field

The utility model relates to a filter, in particular to a multi-mode configurable filter.

Background technique

Filters are one of the most important modules in analog circuits and are widely used in telecommunication equipment and various control systems. The quality of a product often depends on the performance of the filter in the product circuit.

At present, there are mainly two types of integrated circuit filters, continuous time filters and switched capacitor filters. Among them, the continuous time analog filter can be applied to higher frequencies, its transfer function coefficient is determined by the transconductance and capacitance value, the accuracy and linearity are not good, the zero-pole control is complicated, and it is greatly affected by the process; and the switched capacitor filter The transfer function of the device depends on the capacitance ratio and has nothing to do with the process parameters. The transfer function has high precision, and a small capacitor is used to realize a large resistance, which saves area, facilitates integration, and satisfies design directions such as high integration, high precision, and low power consumption. Compared with ordinary filters, configurable multimode filters have the advantage of enabling the same circuit to work in different modes such as low-pass and band-pass through control.

Existing configurable multimode filters can only be configured to work in simple low-pass and band-pass operations, and their working modes are very single.

Utility model content

Aiming at the deficiencies of the prior art, the purpose of this utility model is to provide a multi-mode configurable filter to solve the problem that the existing configurable multi-mode filter can only be configured to work in a single working mode such as simple low-pass and band-pass lack of.

In order to achieve the above object, the utility model adopts the following technical solutions:

A multi-mode configurable filter, the configurable multi-mode filter is composed of an analog signal processing center, a digital control center and a reference voltage current source, and the analog signal processing center is composed of a low-pass band-pass multiplexing filter, hysteresis A comparator, an input stage and an output stage are formed, and the low-pass bandpass multiplexing filter is connected with a hysteresis comparator, an input stage and an output stage; the digital control center is selected by SPI, a clock module, a logic control unit, and a sampling clock Unit, counter and storage register, the logic control unit is connected with SPI, sampling clock selection unit and storage register, and the sampling clock selection unit and logic control unit are all connected with the low-pass band-pass multiplexing filter in the analog signal processing center The clock module is connected with a counter and a storage register, and the counter is connected with the storage register and the hysteresis comparator in the analog signal processing center.

Preferably, the low-pass band-pass multiplexing filter is a fourth-order Butterworth filter formed by cascading two low-Q second-order switched capacitor circuits.

Preferably, the hysteresis comparator is provided with positive and negative feedback paths, and the hysteresis voltage is only generated when the positive feedback coefficient is greater than the negative feedback coefficient.

Preferably, the input stage adopts a double-sampling structure design, which is used to eliminate the influence of amplifier offset and reduce 1/f noise.

Preferably, the output stage is a class AB operational amplifier whose quiescent current is insensitive to process variations.

Preferably, a hysteresis comparison value is set in the storage register, and when the change of the counter result is less than this value, it is determined that it is caused by environmental noise, and the working state of the configured multi-mode filter remains unchanged; when the change of the counting result is greater than the hysteresis comparison value value, it is determined that the change is caused by a change in the fundamental frequency of the input signal, and the multimode filter is configured to adaptively follow the change in the fundamental frequency of the input signal to change its working state.

The configurable multimode filter of the utility model has two working modes, namely fixed mode and adaptive mode, which are configured through SPI:

(1) When working in fixed mode, the configurable multi-mode filter can be configured into four modes: bypass mode, low-pass filter, Q=2 band-pass filter and Q=4 band-pass filter The bandwidth or center frequency of the filter can be configured as 8kHz, 10kHz, 12.5kHz, 16kHz, 20kHz, 25kHz, 32kHz and 40kHz through SPI as required. The input signal V _in is input to the multi-mode filter through the input stage, and directly outputs V _out through the output stage after processing.

(2) When working in adaptive mode, an appropriate low-pass or band-pass filter can be selected according to the frequency of the input signal to process the input signal. At this time, the input signal V _in passes through the input stage to the multimode filter , the output signal V _out is output through the output stage, and at the same time, the real-time feedback loop composed of hysteresis comparator, counter and storage register is fed back to the logic control unit, select low-pass or band-pass, and follow the change of the fundamental frequency of the input signal to adapt the cut-off of the low-pass Frequency or bandpass filter center frequency to filter out low-frequency noise and high-frequency noise of the signal.

The beneficial effects of the utility model are:

The digital control center is used to configure the filter mode, which can make the filter work in bypass mode, low pass, band pass and adaptive mode, and the hysteresis comparator and storage register are used to improve the anti-interference ability, and the performance is good.

Description of drawings

Fig. 1 is the structural block diagram of the configurable multimode filter of the present utility model;

Fig. 2 is the circuit diagram of the low-pass band-pass multiplexing filter of the present utility model;

Fig. 3 is the circuit diagram of hysteresis comparator of the present utility model;

Fig. 4 is the circuit diagram of the input stage of the present utility model;

Fig. 5 is a circuit diagram of the output stage of the present invention.

The labels in the figure are: 1-analog signal processing center, 11-low-pass band-pass multiplexing filter, 12-hysteresis comparator, 13-input stage, 14-output stage, 2-digital control center, 21-SPI, 22 - clock module, 23 - logic control unit, 24 - sampling clock selection unit, 25 - counter, 26 - storage register, 3 - reference voltage and current source.

Detailed ways

Below by embodiment in conjunction with accompanying drawing, the utility model is further described.

A kind of multi-mode configurable filter, as shown in Figure 1, described configurable multi-mode filter is made up of analog signal processing center 1, digital control center 2 and reference voltage current source 3, and described analog signal processing center 1 is made up of Low-pass band-pass multiplexing filter 11, hysteresis comparator 12, input stage 13 and output stage 14 constitute, described low-pass band-pass multiplexing filter 11 is connected with hysteresis comparator 12, input stage 13 and output stage 14; Described digital control center 2 is made of SPI 21, clock module 22, logic control unit 23, sampling clock selection unit 24, counter 25 and storage register 26, and described logic control unit 23 is connected with SPI 21, sampling clock selection unit 24 and The storage register 26, the sampling clock selection unit 24 and the logic control unit 23 are all connected to the low-pass band-pass multiplexing filter 11 in the analog signal processing center 1, and the clock module 22 is connected with a counter 25 and a storage register 26, The counter 25 is connected with the storage register 26 and the hysteresis comparator 12 in the analog signal processing center 2 .

The low-pass band-pass multiplexing filter 11 is a fourth-order Butterworth filter formed by cascading two low-Q second-order switched capacitor circuits, as shown in FIG. 2 . The switches P0, P1 and P2 in the figure control the selection of sampling capacitors and feedback capacitors to realize capacitor multiplexing and make the filter work in three different filtering modes: low-pass, Q=2 band-pass and Q=4 band-pass . The op amp in the filter is a telescopic fully differential amplifier based on switched capacitor common-mode feedback, which provides the high open-loop gain and high input resistance required by the filter. At the same time, the offset voltage of the op-amp is reduced by increasing the input-to-tube area of the op-amp.

The hysteresis comparator 12 is provided with two positive and negative feedback paths, as shown in FIG. 3 , when the positive feedback coefficient is greater than the negative feedback coefficient, the hysteresis voltage is generated. In the figure, M6 and M7 have the same structure, and there are two feedback paths: the current introduced by M5 is negatively fed in series; the voltage generated by M6 and M7 is positively fed back in parallel. Only when β6/β3>1, the hysteresis voltage is generated and the hysteresis voltage can be adjusted with the signal noise to improve the anti-interference ability.

The input stage 13 adopts a double-sampling structure design, as shown in FIG. 4 , which is used to eliminate the influence of amplifier offset and reduce 1/f noise. The input stage performs two functions: converts the single-ended input signal to a differential signal; adjusts the common-mode voltage to adapt to the low-pass filter input common-mode voltage range. The output signal is only related to the input signal and has nothing to do with the offset voltage of the amplifier, thus eliminating the influence of the offset on the performance of the amplifier.

Described output stage 14 is a class AB operational amplifier, as shown in Figure 5, M0～M4 constitutes the first stage differential input stage; M5～M10 constitutes the second stage inverting amplifier, wherein the inverting amplifier formed by M7 (M9) is The M11 (M13) connected to the gate-drain terminal is used as a load, and forms a second-stage non-inverting amplifier together with the pre-stage M6 and M5; M11-M14 form a class AB output stage. Since M11 (M13) connected to the gate-drain terminal can be regarded as a diode load, the smaller equivalent resistance reduces the gain of the second-stage non-inverting amplifier, and the voltage at point A (B) changes little with the process, so its quiescent current Insensitive to process variations.

A hysteresis comparison value is set in the storage register 26, when the counter result variation is less than this value, it is determined that it is caused by environmental noise, and the working state of the configuration multimode filter is kept unchanged; when the counting result variation is greater than the hysteresis comparison value , it is determined that the change is caused by a change in the fundamental frequency of the input signal, and the multimode filter is configured to adaptively follow the change in the fundamental frequency of the input signal to change its working state.

Claims (5)

1. A multi-mode configurable filter, characterized in that: the configurable multi-mode filter is made up of an analog signal processing center (1), a digital control center (2) and a reference voltage current source (3), the The analog signal processing center (1) is composed of a low-pass band-pass multiplexing filter (11), a hysteresis comparator (12), an input stage (13) and an output stage (14), and the low-pass band-pass multiplexing filter (11) is connected with hysteresis comparator (12), input stage (13) and output stage (14); Described digital control center (2) is made of SPI (21), clock module (22), logic control unit (23) , sampling clock selection unit (24), counter (25) and storage register (26) constitute, described logic control unit (23) is connected with SPI (21), sampling clock selection unit (24) and storage register (26), The sampling clock selection unit (24) and the logic control unit (23) are all connected to the low-pass band-pass multiplexing filter (11) in the analog signal processing center (1), and the clock module (22) is connected to a counter (25) and a storage register (26), the counter (25) is connected with the storage register (26) and the hysteresis comparator (12) in the analog signal processing center (1). 2. The multi-mode configurable filter according to claim 1, characterized in that: the low-pass band-pass multiplexing filter (11) is formed by cascading two low-Q second-order switched capacitor circuits A fourth-order Butterworth filter. 3. The multi-mode configurable filter according to claim 1, characterized in that: the hysteresis comparator (12) is provided with two positive and negative feedback paths, and when the positive feedback coefficient is greater than the negative feedback coefficient, the hysteresis voltage only then. 4. The multi-mode configurable filter according to claim 1, characterized in that: the input stage (13) adopts a double-sampling structure design for eliminating the influence of amplifier offset and reducing 1/f noise. 5. The multi-mode configurable filter according to claim 1, characterized in that: a hysteresis comparison value is set in the storage register (26), and when the counter result changes less than this value, it is determined that it is caused by environmental noise If the working state of the configured multi-mode filter is kept unchanged; when the change of the counting result is greater than the hysteresis comparison value, it is determined that the change is caused by the change of the fundamental frequency of the input signal, and the multi-mode filter is configured to adaptively follow the change of the fundamental frequency of the input signal working status.