Multi-mode configurable filter capable of switching low pass and complex band pass based on three-stage operational amplifier

Abstract

The invention belongs to the technical field of communication, and particularly relates to a low-pass and complex-band-pass switchable multimode configurable filter based on a three-stage operational amplifier. The main body structure of the filter is Tow-Thomas, a Chebyshev function is adopted as an approximation function, and the filter comprises two three-stage operational amplifiers and a capacitance-resistance array. The filter has multiple working modes, and different modes are realized by changing the codes of the capacitor array and the resistor array. Antipole split compensation and nested Miller compensation are combined to be used for a three-stage operational amplifier, and the gain bandwidth product of the operational amplifier is increased under the condition that power consumption is not increased; gain tuning and pre-stage output resistance are decoupled by designing an input resistor array, so that the independence of the gain tuning is improved. Configuration and switching of multiple working modes of the active filter are effectively achieved, and the active filter can be applied to receivers of multiple working modes such as satellite communication and navigation and has the advantages of being low in noise, high in linearity, small in-band ripples, easy to integrate, high in practicability and the like.

Description

A multi-mode configurable filter with switchable low-pass and complex bandpass based on a three-stage operational amplifier Technical Field

[0001] This invention belongs to the field of communication technology, specifically relating to a multi-mode configurable filter based on a three-stage operational amplifier that can switch between low-pass and complex bandpass modes, which can be applied to scenarios such as satellite navigation receivers, audio processing systems, and biomedical instruments. Background Technology

[0002] Traditional satellite communication technology, due to the relatively fixed bandwidth supported by receiver systems, typically only allows for a single, specific task to be performed simultaneously, which reduces communication efficiency to some extent. Therefore, the demand for multi-task parallel receiver systems is increasing. This type of receiver requires baseband circuitry that can support different modes and bandwidths, necessitating flexible configuration of circuit parameters. Currently, most receiver circuits support relatively few modes, which is far from sufficient for today's complex and ever-changing application scenarios. Furthermore, existing zero-IF receivers face problems such as high power consumption, low linearity, and high noise.

[0003] Filters are a crucial component of the analog baseband in a receiver, playing a significant role in selecting and filtering signals within the desired frequency band, thus greatly enhancing performance. Traditional filters are categorized as passive and active. Active filters, due to their smaller size and higher integration density, are increasingly widely used. Since multi-channel receivers have varying filter requirements, filters need to be able to operate in different modes to meet different bandwidth and gain demands.

[0004] Currently, the design schemes of active RC filters suffer from limitations in terms of functionality, including: the use of a single or limited number of gain and bandwidth modes, narrow tuning range, inability to decouple gain tuning from interstage resistances, and non-switchable filtering modes. Performance-wise, they exhibit shortcomings such as large in-band ripple, high noise, poor linearity, and poor out-of-band rejection. These functional and performance deficiencies limit the filters' applicability in various scenarios, reducing their practicality. Summary of the Invention

[0005] The purpose of this invention is to provide a multi-mode configurable filter based on a three-stage operational amplifier that can switch between low-pass and complex bandpass modes, with good tuning performance and high operating efficiency. It has variable bandwidth, gain and center frequency, and supports both low-pass and complex bandpass filtering modes.

[0006] The multimode configurable filter based on a three-stage operational amplifier, allowing for switchable low-pass and complex band-pass operation, primarily employs two Tow-Thomas dual second-order structures. Specifically, it includes an operational amplifier, a bridging resistor array, and a filter mode switching switch; wherein:

[0007] The operational amplifier employs a three-stage fully differential structure, including an input stage, an intermediate stage, an output stage, and common-mode feedback. The currents of both the input and output stages can be controlled by changing the encoding. The input stage includes a common-mode resistor array. Stability is improved by employing a combination of nested Miller compensation and anti-pole splitting compensation.

[0008] The bridging resistor array contains four resistor array and 4 A resistor array, the aforementioned resistor array being used to tune the center frequency.

[0009] The filter mode switching switch is connected in series with the bridging resistor array and is used to switch between low-pass and complex band-pass filters.

[0010] In addition, it includes 4 input resistor arrays, 4 feedback resistor arrays, and 4... Capacitor array, 4 The capacitor array, along with the resistor array, is used for bandwidth and gain tuning.

[0011] Furthermore:

[0012] The filter body adopts a fully differential topology and the approximation function is the Chebyshev function.

[0013] The input resistor array comprises two groups: a positive terminal and a negative terminal. Each group includes one fixed branch and 14 adjustable ranges. Each adjustable branch includes a resistor and a gain tuning switch. The positive and negative branches are connected by a shorting switch, whose control signals are opposite to those of the gain tuning switch. Adjustable branches nine through fourteen also include input resistor tuning switches. Specifically, the fixed branch resistance is R. i0 = 25.6 kΩ, the resistance of the first adjustable branch is R i1 = 60.5 kΩ, the resistance of the second adjustable branch is R i2 = 42.7 kΩ, the resistance of the third adjustable branch is R i3 = 30.2 kΩ, the resistance of the fourth adjustable branch is R i4 = 21.4 kΩ, the resistance of the fifth adjustable branch is R i5 = 15.1 kΩ, the resistance of the sixth adjustable branch is R i6 = 10.6 kΩ, the resistance of the seventh adjustable branch is R i7 = 7.5 kΩ, the resistance of the eighth adjustable branch is R i8 = 5.3 kΩ, the resistance of the ninth adjustable branch is R i9 = 3.5 kΩ, the resistance of the tenth adjustable branch is R i10= 2.5kΩ, the adjustable branch resistance of Article 11 is R i11 = 2 kΩ, the resistance of the twelfth adjustable branch is R i12 = 1.2 kΩ, the resistance of the thirteenth adjustable branch is R i13 = 1 kΩ, the resistance of the fourteenth adjustable branch is R i14 = 500 Ω.

[0014] The feedback resistor R fb The array contains 3-bit adjustable ranges; specifically, the resistance of the first adjustable branch is R. 20 = 12.8 kΩ, the resistance of the second adjustable branch is R 21 = 6.4 kΩ, the resistance of the third adjustable branch is R 22 = 6.4 kΩ.

[0015] The aforementioned The resistor array contains 3 adjustable ranges. Specifically, the resistor in the first adjustable branch is R. 20 =1.5 kΩ, the resistance of the second adjustable branch is R 21 = 1.5 kΩ, the resistance of the third adjustable branch is R 22 = 1 kΩ.

[0016] The aforementioned The resistor array contains 3 adjustable ranges. Specifically, the resistor in the first adjustable branch is R. 20 =500 Ω, the resistance of the second adjustable branch is R 21 = 1.5 kΩ, the resistance of the third adjustable branch is R 22 = 1 kΩ.

[0017] The aforementioned The capacitor array contains 8 adjustable levels. Specifically, the capacitor of the first adjustable branch is C. 10 =85 fF, the capacitance of the second adjustable branch is C. 11 = 170 fF, the third adjustable branch capacitor is C 12 = 340 fF, the fourth adjustable branch capacitor is C 13 = 680 fF, the fourth adjustable branch capacitor is C 14 = 1.36 pF, the fifth adjustable branch capacitor is C 15 = 2.72 pF, the capacitance of the sixth adjustable branch is C 16 = 5.44 pF, the capacitor of the seventh adjustable branch is C 17 =10.88 pF, the capacitance of the eighth adjustable branch is C 18 = 21.76 pF. Capacitor array and The structure and capacitance values ​​of the capacitor array are the same.

[0018] In the operational amplifier described, the input stage is a five-transistor operational transconductance amplifier with NMOS input, the intermediate stage is a common-source stage, and the output stage is a Class AB amplifier.

[0019] In the operational amplifier described, the input stage current-tunable module includes a tunable current mirror and a tunable load. The tunable current mirror includes one fixed branch and three adjustable levels. Specifically, the fixed branch current is 80 μA, the first adjustable branch current is 160 μA, the second adjustable branch current is 80 μA, and the third adjustable branch current is 40 μA. The tunable load modes correspond one-to-one with the tunable current mirror.

[0020] In the operational amplifier described, the output stage current-tunable module includes one fixed branch and three adjustable levels. Specifically, the fixed branch current is 54 μA, the first adjustable branch current is 52 μA, the second adjustable branch current is 26 μA, and the third adjustable branch current is 13 μA.

[0021] In the aforementioned bridging resistor array, The resistor array contains 6 adjustable ranges. Specifically, the first adjustable branch resistor is R. 10 = 1.6 kΩ, the resistance of the second adjustable branch is R 11 = 60 Ω, the resistance of the third adjustable branch is R 12 = 320 Ω, the resistance of the fourth adjustable branch is R 13 = 710 Ω, the resistance of the fifth adjustable branch is R 14 = 190 Ω, the resistance of the sixth adjustable branch is R 15 = 520 Ω.

[0022] In the aforementioned bridging resistor array, The resistor array contains 6 adjustable ranges. Specifically, the first adjustable branch resistor is R. 10 = 1 kΩ, the resistance of the second adjustable branch is R 11 = 130 Ω, the resistance of the third adjustable branch is R 12 = 300 Ω, the resistance of the fourth adjustable branch is R 13 = 240 Ω, the resistance of the fifth adjustable branch is R 14 = 220 Ω, the resistance of the sixth adjustable branch is R 15 = 500 Ω.

[0023] Technical features of the present invention:

[0024] (1) To address the non-ideal effects of the operational amplifier, this invention employs a three-stage fully differential structure. The first stage is a five-transistor operational transconductance amplifier with NMOS input, the intermediate stage is a common source amplifier, and the output stage is a Class AB amplifier. By increasing the gain of the operational amplifier, the non-ideal effects it introduces can be reduced as much as possible.

[0025] (2) To address the increased in-band ripple caused by operational amplifiers under large bandwidth, this invention is the first to combine tunable anti-pole splitting compensation with nested Miller compensation in a three-stage operational amplifier. The capacitor in the anti-pole splitting compensation acts as a "negative capacitor," introducing an additional zero, which increases the gain-bandwidth product of the operational amplifier and avoids the frequency peaking effect that occurs in the filter under large bandwidth. At the same time, the passive circuit does not introduce additional power consumption, thus improving flatness with minimal power consumption.

[0026] (3) For the input resistor array, if only a single switch is used to control different resistor branches, the output resistance of the preceding circuit will change while the gain is changed. To solve this problem, this invention effectively ensures that the interstage resistance remains constant by setting a gain tuning switch, an input resistor tuning switch, and a positive and negative terminal shorting switch. Among them, the control signals of the gain tuning switch and the positive and negative terminal shorting switch are always opposite. When the gain switch of a certain branch is turned on, the positive and negative terminal shorting switch of the corresponding branch is turned off. This branch provides a certain input resistance for the filter. Due to the virtual short and virtual open effects of the op-amp, the positive and negative terminals of this branch are shorted for the preceding circuit. In any gain mode, the output resistance of the preceding circuit is the parallel connection of all resistors and is a constant value. This effectively solves the coupling problem between gain tuning and interstage resistance.

[0027] (4) To address the filter linearity issue, a Class AB amplifier was used at the output of the operational amplifier, improving the filter's linearity. Simultaneously, an additional PMOS switch was used for the capacitor array unit. This PMOS switch shares the same control signal as the NMOS switch in the same branch. When the capacitor branch is off, the PMOS switch conducts, ensuring that the voltage between the capacitor and the NMOS switch does not float and becomes the output voltage of the operational amplifier. This effectively improves the filter's in-band performance. .

[0028] (5) Regarding noise performance, it is divided into thermal noise and flicker noise. The main contributors to thermal noise are the input resistance and... And it is positively correlated with the input resistance, and with The correlation is negative. By setting appropriate resistance values, thermal noise in the circuit is reduced. The main contributors to flicker noise are the input transistors and input load of the first-stage operational amplifier. Increasing the input stage area effectively reduces flicker noise and improves the filter's signal-to-noise ratio.

[0029] The functional advantages of this invention:

[0030] (1) Implement multiple working modes to meet the needs of different application scenarios

[0031] The operating modes include switchable low-pass and complex bandpass, with three different bandwidths: 8 MHz, 10 MHz, and 25 MHz. The gain range is 0 dB to 15 dB with a step size of 3 dB, and it has two different center frequencies: 15 MHz and 25 MHz. These variable parameters can be combined arbitrarily to form 54 different operating modes, improving the flexibility and independence of tuning and meeting the needs of a wide range of application scenarios.

[0032] (2) It has the characteristics of low noise, high linearity, high input range and low power consumption.

[0033] This invention effectively reduces filter noise by setting a reasonable resistor and transistor width-to-length ratio. Simultaneously, it employs a capacitor array unit and operational amplifier structure with improved linearity to enhance in-band performance. It provides a stable input voltage range. By setting the op-amp's tunable input and output units, power consumption is saved at low bandwidths.

[0034] (3) It achieves decoupling of gain tuning and interstage resistance, thereby improving the versatility of the circuit.

[0035] Different switches are set in the input resistor array to independently tune the input resistance and gain. During gain tuning from 0 dB to 15 dB, only the encoding of the gain switch is changed, keeping the input resistance constant. This avoids the performance degradation of the preceding module caused by changes in interstage resistance due to gain changes.

[0036] (4) To avoid frequency peaking, the gain-bandwidth product of the three-stage operational amplifier is increased without increasing power consumption or deteriorating stability. This is achieved by combining inverse pole splitting compensation with nested Miller compensation, which introduces additional zeros into the operational amplifier. This passive branch does not increase power consumption, but increases the gain-bandwidth product, preventing ripples in the frequency response of the filter under large bandwidth and improving in-band flatness. Attached Figure Description

[0037] Figure 1 is a schematic diagram of the overall structure of the low-pass and complex bandpass switchable multimode configurable filter of the present invention.

[0038] Figure 2 is a transistor-level circuit diagram of the operational amplifier in this invention.

[0039] Figure 3 shows the input resistor array R in this invention. in Transistor-level circuit diagram.

[0040] Figure 4 shows the invention. and Transistor-level circuit diagram of a resistor array.

[0041] Figure 5 shows R1, R2, and R in this invention. fb Transistor-level circuit diagram of a resistor array.

[0042] Figure 6 shows the invention. and Transistor-level circuit diagram of a capacitor array.

[0043] Figure 7 shows the frequency response curves of the present invention at different gains in the low-pass operating mode with a bandwidth of 8 MHz.

[0044] Figure 8 shows the frequency response curves of the present invention at different gains in low-pass operating mode with a bandwidth of 10 MHz.

[0045] Figure 9 shows the frequency response curves of the present invention at different gains in low-pass operating mode with a bandwidth of 25 MHz.

[0046] Figure 10 shows the frequency response curves of the present invention under different gains in the complex bandpass operating mode with a single-sided bandwidth of 8 MHz and a center frequency of 15 MHz.

[0047] Figure 11 shows the frequency response curves of the present invention under different gains in the complex bandpass operating mode with a single-sided bandwidth of 10MHz, a center frequency of 15MHz, and a single-sided bandwidth of 10MHz.

[0048] Figure 12 shows the frequency response curves of the present invention under different gains in the complex bandpass operating mode with a single-sided bandwidth of 25 MHz, a center frequency of 15 MHz, and a single-sided bandwidth of 25 MHz.

[0049] Figure 13 shows the frequency response curves of the present invention under different gains in the complex bandpass operating mode with a single-sided bandwidth of 8 MHz and a center frequency of 25 MHz.

[0050] Figure 14 shows the frequency response curves of the present invention under different gains in the complex bandpass operating mode with a single-sided bandwidth of 10 MHz and a center frequency of 25 MHz.

[0051] Figure 15 shows the frequency response curves of the present invention under different gains in the complex bandpass operating mode with a single-sided bandwidth of 25 MHz, a center frequency of 25 MHz, and a single-sided bandwidth of 25 MHz.

[0052] Figure 16 shows the output voltage noise curve of the present invention with a bandwidth of 25 MHz and a gain of 15 dB.

[0053] Figure 17 shows the common-mode stability curve of the operational amplifier in this invention.

[0054] Figure 18 shows the differential-mode stability curve of the operational amplifier in this invention.

[0055] Figure 19 shows the harmonic simulation curve at the output end of the present invention.

[0056] Figure 20 shows the simulation curve of the common-mode voltage range at the input terminal of the present invention.

[0057] The diagram labels are as follows: 101 is the first-stage operational amplifier (I-channel), 102 is the second-stage operational amplifier (I-channel), 103 is the input resistor array (I-channel), 104 is the feedback resistor array (I-channel), and 105 is the input resistor array (I-channel). Resistor array, 106 I-channel Resistor array, 107 is an I-channel Capacitor array, 108 I / O channels The resistor array consists of resistors: 109 for the first stage Q-channel operational amplifier, 110 for the second stage Q-channel operational amplifier, 111 for the input Q-channel resistor array, 112 for the feedback Q-channel resistor array, and 113 for the feedback Q-channel resistor array. Resistor array, 114 is Q-channel Resistor array, 115 is a Q-channel Capacitor array, 116 is a Q-channel Resistor array, 117 Resistor array, 118 Resistor array, 119 is AND Serial filter mode switching switch, 120 is connected to A series-connected filter mode switching switch. Detailed Implementation

[0058] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0059] Example 1 provides a switchable low-pass and complex band-pass multimode configurable filter, the overall structure of which is shown in Figure 1. This filter includes four operational amplifiers 101, 102, 109, and 110, input resistor arrays 103 and 111, and feedback resistor arrays 104 and 112. Capacitor arrays 107 and 115, Capacitor arrays 108 and 116, 4 Resistor array 117, 4 Resistor array 118, 4 switches 119, 4 switches 120. Among them:

[0060] Connect to V A The nodes are: the negative input terminal of operational amplifier 101, R in V of resistor array 103 opa1,in+ In switch 119, M c11 The source pole, R fb V of resistor array 104 rin R1 resistor array 105 V rin V of C1 capacitor array 107 cin .

[0061] Connect to VB The nodes are: the positive output terminal of operational amplifier 101, and the V of resistor array 105 (R1). rout V of C1 capacitor array 107 cout R cross1 V of resistor array 117 rout The V of resistor array 106 of R2 rout .

[0062] Connect to V C The nodes are: the positive input terminal of operational amplifier 101, R in V of resistor array 103 opa1,in- In switch 119, M c13 The source pole, R fb V of resistor array 104 rin R1 resistor array 105 V rin V of C1 capacitor array 107 cin .

[0063] Connect to V D The nodes are: the negative output terminal of operational amplifier 101, and the V of resistor array 105 (R1). rout V of C1 capacitor array 107 cout R cross1 V of resistor array 117 rout The V of resistor array 106 of R2 rout .

[0064] Connect to V E The nodes are: the negative input terminal of operational amplifier 102, and the V of resistor array 106. rin Switch 120 M c21 The source of the C2 capacitor array 108 V cin .

[0065] Connect to V out_i+ The nodes are: the positive output terminal of operational amplifier 102, and the V of capacitor array 108 (C2). cout R cross2 V of resistor array 118 rout R fb V of resistor array 104 rout .

[0066] Connect to V F The nodes are: the positive input terminal of operational amplifier 102, and the V of resistor array 106. rin Switch 120 M c23 The source of the C2 capacitor array 108 V cin .

[0067] Connect to V out_i-The nodes are: the negative output terminal of operational amplifier 102, and the V of capacitor array 108 (C2). cout R cross2 V of resistor array 118 rout R fb V of resistor array 104 rout .

[0068] Connect to V G The nodes are: the negative input terminal of operational amplifier 109, R in V of resistor array 111 opa1,in+ In switch 119, M c12 The source pole, R fb V of resistor array 112 rin V of resistor array 113, R1 rin V of C1 capacitor array 115 cin .

[0069] Connect to V H The nodes are: the positive output terminal of operational amplifier 109, and the V of resistor array 113 (R1). rout V of C1 capacitor array 115 cout R cross1 V of resistor array 117 rout V of resistor array 114, R2 rout .

[0070] Connect to V I The nodes are: the positive input terminal of operational amplifier 109, R in V of resistor array 111 opa1,in- In switch 119, M c14 The source pole, R fb V of resistor array 112 rin V of resistor array 113, R1 rin V of C1 capacitor array 115 cin .

[0071] Connect to V J The nodes are: the negative output terminal of operational amplifier 109, and the V of resistor array 113. rout V of C1 capacitor array 115 cout R cross1 V of resistor array 117 rout V of resistor array 114, R2 rout .

[0072] Connect to V K The nodes are: the negative input terminal of operational amplifier 110, and the V of resistor array 114. rin Switch 120 M c22The source of the capacitor array 116, V cin .

[0073] Connect to V out_q+ The nodes are: the positive output terminal of operational amplifier 110, and the V of capacitor array 116 (C2). cout R cross2 V of resistor array 118 rout R fb V of resistor array 112 rout .

[0074] Connect to V L The nodes are: the positive input terminal of operational amplifier 110, and the V of resistor array 114 (R2). rin Switch 120 M c24 The source of the capacitor array 116, V cin .

[0075] Connect to V out_q- The nodes are: the negative output terminal of operational amplifier 110, and the V of capacitor array 116 (C2). cout R cross2 V of resistor array 118 rout R fb V of resistor array 112 rout .

[0076] In this embodiment, the power supply voltage is 1.05 V, the reference voltage is 520 mV, and the bias current at the input of each operational amplifier is 10 μA. The input voltage signals of the I / Q channels are quadrature signals with the same amplitude.

[0077] In this embodiment, feedback resistor arrays 104 and 112, Resistor arrays 105 and 113, Resistor arrays 106 and 114, Capacitor arrays 107 and 115, Each branch switch in capacitor arrays 108 and 116 is connected to the input of the operational amplifier to avoid a large output signal swing that would reduce linearity.

[0078] In this embodiment, the operating states of switches 119 and 120 must be the same, that is, the gate voltages must be either high or low simultaneously. When switches 119 and 120 are off, the circuit operates in low-pass filter mode; when switches 119 and 120 are on, the circuit operates in complex band-pass filter mode.

[0079] In this embodiment, the bandwidth, gain, and center frequency are determined by the capacitors and resistors. By setting the appropriate resistor and capacitor values, the Q value of this filter is consistently 0.707 in different operating modes, exhibiting good in-band flatness. The transfer function of this filter is:

[0080]

[0081] The bandwidth of a low-pass filter (the single-sided bandwidth of a complex band-pass filter) is:

[0082]

[0083] The value of Q is:

[0084]

[0085] The center frequency is:

[0086] .

[0088] Example 2 provides a transistor-level circuit for an operational amplifier. As shown in Figure 2, the operational amplifier employs a three-stage fully differential circuit structure. Wherein, , , , and A five-transistor operational transconductance amplifier with NMOS input. This is a tunable current mirror for the input stage, where the tunable current can be configured by setting different width-to-length ratios. and It is an input stage tunable load.

[0089] In this embodiment, ~ and ~ These two sets of common source electrodes form the intermediate stage of the operational amplifier.

[0090] In this embodiment, specifically, , and , These form two Class AB amplifiers, which are the output stages of the operational amplifiers. Unlike Class A or Class B amplifiers, Class AB amplifiers have a conduction angle between 180° and 360°, ensuring a larger output voltage swing and better linearity.

[0091] In this embodiment, the operational amplifier employs a combination of nested Miller compensation and anti-pole splitting compensation. Miller capacitance C c1a,b and zero-adjustment resistor R z1a,band Miller capacitance C c2a,b and zero-adjustment resistor R z2a,b These are connected between the output stage and the input stage, and between the output stage and the intermediate stage, respectively. Miller capacitors are used to separate the dominant and secondary poles, improving the phase margin. Since a three-stage op-amp produces a zero in the right half-plane, this zero causes a large phase shift, worsening the phase margin, and this zero cannot be easily canceled out by poles, a zero-adjustment resistor is needed to shift it towards the left half-plane or infinity. Anti-pole splitting compensation C c3a,b and R z3a,b The gain-bandwidth product of the op-amp is improved without increasing power consumption, and combined with nested Miller compensation, the stability of the op-amp is guaranteed.

[0092] Example 3 provides a transistor-level circuit for an input resistor array. As shown in Figure 3, the input resistor array is divided into positive and negative terminals. Each terminal contains one fixed branch and 14 adjustable branches. The resistance of the fixed branch is R. i0 = 25.6 kΩ, the resistance of the first adjustable branch is R i1 = 60.5 kΩ, the resistance of the second adjustable branch is R i2 = 42.7 kΩ, the resistance of the third adjustable branch is R i3 = 30.2 kΩ, the resistance of the fourth adjustable branch is R i4 = 21.4 kΩ, the resistance of the fifth adjustable branch is R i5 = 15.1 kΩ, the resistance of the sixth adjustable branch is R i6 = 10.6 kΩ, the resistance of the seventh adjustable branch is R i7 =7.5 kΩ, the resistance of the eighth adjustable branch is R i8 = 5.3 kΩ, the resistance of the ninth adjustable branch is R i9 = 3.5 kΩ, the resistance of the tenth adjustable branch is R i10 = 2.5 kΩ, the adjustable branch resistance of Article 11 is R i11 = 2 kΩ, the resistance of the twelfth adjustable branch is R i12 = 1.2 kΩ, the resistance of the thirteenth adjustable branch is R i13 = 1 kΩ, the resistance of the fourteenth adjustable branch is R i14 = 500 Ω.

[0093] In this embodiment, it is assumed that the unit resistance is... = 1.6 kΩ, therefore we can obtain = 16 The resistance value of the nth adjustable branch can be calculated using the following formula:

[0094]

[0095] In this embodiment, specifically, the switch ~ and ~ Used for adjusting gain, switch ~ Connected between the positive and negative input resistors, its control signal is opposite to the gain tuning switch signal. ~ and ~ Used to change the output resistance of the preceding circuit.

[0096] In this embodiment, the signal and The input resistance is a single-ended equivalent resistance, which determines the gain of the filter and varies with the number of gain tuning switches that are turned on and off. and The output resistor is between the two resistors. Due to the virtual short and virtual open effects of the operational amplifier, the positive and negative terminals of the branch resistor that is turned off by the gain switch are still connected. Therefore, under any gain condition, the output resistor of the front stage is the parallel connection of all the resistors in the array and remains unchanged.

[0097] In this embodiment, the on-resistance and off-resistance of the switch can be affected by changes in temperature, voltage, etc., in certain branches with lower resistance values. Therefore, it is necessary to adjust the size of the MOSFET according to the branch resistance to change the on-resistance and off-resistance. In this invention, the ratio of the on-resistance of the MOSFET in the nth branch to the resistance of that branch is designed to be a constant. Since the on-resistance of the MOSFET is inversely proportional to its width W and directly proportional to its length L, the width-to-length ratio of the MOSFET in the low-resistance branch is relatively large to ensure that the change in on-resistance is small.

[0098] Example 4, providing and The transistor-level circuit of the resistor array is shown in Figure 4. The resistors connected to the circuit are selected and controlled by switching the switches on and off. Only one switch can be on at a time, and the rest must be off.

[0099] In this embodiment, the conduction of each switch corresponds to a bandwidth mode. When the switch... When conducting, the resistance Connected to the circuit; when the switch When conducting, the resistance Connected to the circuit; when the switch When conducting, the resistance Connected to the circuit; when the switch When conducting, the resistance Connected to the circuit; when the switch When conducting, the resistance Connected to the circuit; when the switch When conducting, the resistance The circuit is connected.

[0100] Example 5 provides R1, R2 and R fb The transistor-level circuit of the resistor array is shown in Figure 5. The resistors connected to the circuit are selected and controlled by switching the switches on and off. Only one switch can be on at a time, and the rest must be off.

[0101] In this embodiment, when the switch When conducting, the resistance Connected to the circuit; when the switch When conducting, the resistance Connected to the circuit; when the switch When conducting, the resistance The circuit is connected.

[0102] Example 6, providing and The transistor-level circuit of the capacitor array is shown in Figure 6. The control signals for the NMOS and PMOS switches are the same. The on / off state of the NMOS switch determines whether the capacitor branch is connected to the circuit. The PMOS switch improves the linearity of the filter. When the NMOS switch is off, without the PMOS switch, the voltage between the capacitor and the switch is floating. With the PMOS switch on, the PMOS switch conducts, and the voltage between the capacitor and the switch is equal to the output voltage of the operational amplifier, thus improving the linearity of the filter.

[0103] Example 7, Figure 7 shows the frequency response curves of the present invention at different gains in a low-pass operating mode with a bandwidth of 8 MHz. When operating in this mode, = 4 kΩ, = 3 kΩ, = 3.5 pF, = 5.9 pF. Low-frequency gain range is 0 dB to 15 dB in 3 dB increments. At 8 MHz, the gain drops by 3 dB compared to the in-band.

[0104] Figure 8 shows the frequency response curves of the present invention at different gains in a 10 MHz low-pass operating mode. When operating in this mode, = 3 kΩ, = 2 kΩ, = 3.8 pF, = 5.3 pF. Low-frequency gain range is 0 dB to 15 dB in 3 dB increments. At 10 MHz, the gain drops by 3 dB compared to the in-band.

[0105] Figure 9 shows the frequency response curves of the present invention at different gains in low-pass operating mode with a bandwidth of 25 MHz. When operating in this mode, = 1.5 kΩ, = 500 Ω, = 3 pF, = 4.2 pF. Low-frequency gain range is 0 dB to 15 dB in 3 dB increments. At 25 MHz, the gain drops by 3 dB compared to the in-band.

[0106] Figure 10 shows the frequency response curves of the present invention at different gains in the complex bandpass operating mode with a single-sided bandwidth of 8 MHz and a center frequency of 15 MHz. When operating in this mode, = 4 kΩ, = 3 kΩ, = 3.5 pF, = 5.9pF, = 3 kΩ, = 1.8 kΩ. Low-frequency gain range is 0 dB to 15 dB in 3 dB increments. Gain decreases by 3 dB compared to in-band at 7 MHz and 23 MHz.

[0107] Figure 11 shows the frequency response curves of the present invention under different gains in complex bandpass operating mode with a single-sided bandwidth of 10MHz and a center frequency of 15MHz. When operating in this mode... = 3 kΩ, = 2 kΩ, = 3.8 pF, = 5.3pF, = 2.8 kΩ, = 2 kΩ. Low-frequency gain range is 0 dB to 15 dB in 3 dB increments. Gain decreases by 3 dB compared to in-band at 5 MHz and 25 MHz.

[0108] Figure 12 shows the frequency response curves of the present invention at different gains in the complex bandpass operating mode with a single-sided bandwidth of 25 MHz and a center frequency of 15 MHz. When operating in this mode, = 1.5 kΩ, = 500 Ω, = 3 pF, =4.2 pF, = 3.5 kΩ, = 2.5 kΩ. Low-frequency gain range is 0 dB to 15 dB in 3 dB increments. At 40 MHz, the gain drops by 3 dB compared to the in-band.

[0109] Figure 13 shows the frequency response curves of the present invention at different gains in the complex bandpass operating mode with a single-sided bandwidth of 8 MHz and a center frequency of 25 MHz. When operating in this mode, = 4 kΩ, = 3 kΩ, = 3.5 pF, = 5.9pF, = 1.8 kΩ, = 1.1 kΩ. Low-frequency gain range is 0 dB to 15 dB in 3 dB increments. Gain drops by 3 dB at 17 MHz and 33 MHz compared to in-band.

[0110] Figure 14 shows the frequency response curves of the present invention at different gains in the complex bandpass operating mode with a single-sided bandwidth of 10 MHz and a center frequency of 25 MHz. When operating in this mode, = 3 kΩ, = 2 kΩ, = 3.8 pF, = 5.3pF, = 1.7 kΩ, = 1.2 kΩ. Low-frequency gain range is 0 dB to 15 dB in 3 dB increments. Gain drops by 3 dB compared to in-band at 15 MHz and 35 MHz.

[0111] Figure 15 shows the frequency response curves of the present invention at different gains in the complex bandpass operating mode with a single-sided bandwidth of 25 MHz and a center frequency of 25 MHz. When operating in this mode, = 1.5 kΩ, = 500 Ω, = 3 pF, =4.2 pF, = 2.1 kΩ, = 1.5 kΩ. Low-frequency gain range is 0 dB to 15 dB in 3 dB increments. Gain drops by 3 dB at 0 MHz and 50 MHz compared to in-band.

[0112] In this embodiment, the feedback resistor is 6.4 kΩ, and the gain is 0 dB. = 6.4 kΩ; at a gain of 3 dB, = 4.5 kΩ; at a gain of 6 dB, = 3.2 kΩ; at a gain of 9 dB, = 2.3 kΩ; at a gain of 12 dB, = 1.6 kΩ; at a gain of 15 dB, = 1.1 kΩ.

[0113] Example 8 provides an output noise profile with a bandwidth of 25 MHz and a gain of 15 dB, as shown in Figure 16. The output noise voltage at 100 kHz is 281.2. The output noise voltage at 1 MHz is 105.1. The output noise voltage at 10 MHz is 90. Since the output noise is affected by the system gain, the equivalent input integral noise is used, resulting in an equivalent input integral noise of 6.9. It has good noise performance.

[0114] Example 9 provides the common-mode and differential-mode stability curves of an operational amplifier, as shown in Figures 17 and 18. This operational amplifier has a common-mode loop gain of 48.4 dB and a common-mode phase margin of 74.43° at 120 MHz. The differential-mode loop gain is 62.4 dB, and the differential-mode phase margin is 53.60° at 550 MHz, indicating good operational amplifier stability.

[0115] Example 10 provides the harmonic simulation curves at the filter output, as shown in Figure 19. The input dual-tone frequencies are 24 MHz and 25 MHz, and the input voltage amplitude is 20 mV. The output power at both dual tones is 0 dB, and the third harmonic at 23 MHz is -80.6 dBm. The in-band power of this filter can be calculated. It has a linearity of 40.3 dBm, which is high.

[0116] Example 11 provides a simulation curve of the input common-mode voltage range, as shown in Figure 20. The input provides a time-varying reference voltage, which changes every 5 μs, rising from 390 mV to 700 mV and then falling back to 390 mV. Within this range, the output voltage shows no oscillations or significant deviations, indicating a large stable input voltage range for this circuit.

Claims

1. A multi-mode configurable filter based on a three-stage operational amplifier, switchable between low-pass and complex bandpass, characterized in that, The main body adopts two Tow-Thomas dual second-order structures, specifically including operational amplifiers, a bridging resistor array, and a filter mode switching switch; wherein: the operational amplifier adopts a three-stage fully differential structure, including an input stage, an intermediate stage, an output stage, and common-mode feedback; the input stage and output stage currents are both controlled by changing the code; a compensation method combining nested Miller compensation and anti-pole splitting compensation is used to improve stability; the bridging resistor array contains four resistor array and 4 A resistor array is used to tune the center frequency; the filter mode switching switch, connected in series with the resistor array, is used to switch between low-pass and complex band-pass filters; in addition, it also includes 4 input resistor arrays, 4 feedback resistor arrays, and 4... Capacitor array, 4 The capacitor array, along with the resistor array, is used for bandwidth and gain tuning.

2. The multimode configurable filter according to claim 1, characterized in that: The input resistor array comprises two groups, positive and negative, each containing one fixed branch and 14 adjustable ranges. Each adjustable branch includes a resistor and a gain tuning switch. The positive and negative branches are connected by a shorting switch, whose control signals are opposite to those of the gain tuning switch. The ninth to fourteenth adjustable branches also include input resistor tuning switches. The feedback resistor array contains 3 adjustable ranges. The resistor array includes 3-bit adjustable ranges; The resistor array includes 3-bit adjustable ranges; The capacitor array includes 8-bit adjustable levels; Capacitor array, containing 8-bit adjustable levels.

3. The multimode configurable filter according to claim 2, characterized in that, In the operational amplifier described above: the input stage is a five-transistor operational transconductance amplifier with NMOS input, the intermediate stage is a common-source stage, and the output stage is a Class AB amplifier. The input stage current tunable module includes a tunable current mirror and a tunable load; the tunable current mirror includes one fixed branch and three adjustable ranges; the output stage current tunable module includes one fixed branch and three adjustable ranges.

4. The multimode configurable filter according to claim 3, characterized in that, Each operational amplifier contains four Miller compensation branches, forming a nested Miller compensation system. Two branches are connected between the output stage and the intermediate stage, and two branches are connected between the output stage and the input stage.

5. The multimode configurable filter according to claim 4, characterized in that, In the aforementioned bridging resistor array: The resistor array contains 6-bit adjustable ranges; The resistor array contains 6-bit adjustable ranges.

6. The multimode configurable filter according to claim 5, characterized in that, The input resistor array comprises two groups: a positive terminal and a negative terminal. Each group contains one fixed branch and 14 adjustable ranges. The ninth to fourteenth adjustable branches also include an input resistor tuning switch. Specifically, the fixed branch resistance is R. i0 = 25.6 kΩ, the resistance of the first adjustable branch is R i1 = 60.5 kΩ, the resistance of the second adjustable branch is R i2 = 42.7 kΩ, the resistance of the third adjustable branch is R i3 = 30.2 kΩ, the resistance of the fourth adjustable branch is R i4 = 21.4 kΩ, the resistance of the fifth adjustable branch is R i5 = 15.1 kΩ, the resistance of the sixth adjustable branch is R i6 =10.6 kΩ, the resistance of the seventh adjustable branch is R i7 = 7.5 kΩ, the resistance of the eighth adjustable branch is R i8 = 5.3 kΩ, the resistance of the ninth adjustable branch is R i9 = 3.5 kΩ, the resistance of the tenth adjustable branch is R i10 = 2.5 kΩ, the adjustable branch resistance of Article 11 is R i11 = 2 kΩ, the resistance of the twelfth adjustable branch is R i12 = 1.2 kΩ, the resistance of the thirteenth adjustable branch is R i13 = 1 kΩ, the resistance of the fourteenth adjustable branch is R i14 = 500 Ω.

7. The multimode configurable filter according to claim 6, characterized in that: The feedback resistor R fb The array contains 3 adjustable ranges; specifically, the resistance of the first adjustable branch is R. 20 =12.8 kΩ, the resistance of the second adjustable branch is R 21 = 6.4 kΩ, the resistance of the third adjustable branch is R 22 = 6.4 kΩ; the aforementioned The resistor array contains 3 adjustable ranges; specifically, the first adjustable branch resistor is R. 20 = 1.5 kΩ, the resistance of the second adjustable branch is R 21 = 1.5 kΩ, the resistance of the third adjustable branch is R 22 = 1 kΩ; the aforementioned The resistor array contains 3 adjustable ranges; specifically, the first adjustable branch resistor is R. 20 = 500 Ω, the resistance of the second adjustable branch is R 21 = 1.5 kΩ, the resistance of the third adjustable branch is R 22 = 1 kΩ; the aforementioned The capacitor array contains 8 adjustable levels; specifically, the capacitor in the first adjustable branch is C. 10 = 85 fF, the second adjustable branch capacitor is C 11 = 170 fF, the third adjustable branch capacitor is C 12 = 340 fF, the fourth adjustable branch capacitor is C 13 = 680 fF, the fifth adjustable branch capacitor is C 14 = 1.36 pF, the capacitance of the sixth adjustable branch is C 15 = 2.72 pF, the capacitor of the seventh adjustable branch is C 16 = 5.44 pF, the capacitance of the eighth adjustable branch is C 17 = 10.88pF, Capacitor array and The structure and capacitance values ​​of the capacitor array are the same.

8. The multimode configurable filter according to claim 7, characterized in that, In the operational amplifier described above: the tunable current mirror includes one fixed branch and three adjustable levels, specifically, the fixed branch current is 80 μA, the first adjustable branch current is 160 μA, the second adjustable branch current is 80 μA, and the third adjustable branch current is 40 μA; the tunable load modes correspond one-to-one with the tunable current mirror; the output stage current tunable module includes one fixed branch and three adjustable levels, specifically, the fixed branch current is 54 μA, the first adjustable branch current is 52 μA, the second adjustable branch current is 26 μA, and the third adjustable branch current is 13 μA.

9. The multimode configurable filter according to claim 8, characterized in that, In the aforementioned bridging resistor array: The resistor array contains 6 adjustable ranges; specifically, the first adjustable branch resistor is R. 10 = 1.6 kΩ, the resistance of the second adjustable branch is R 11 = 60 Ω, the resistance of the third adjustable branch is R 12 = 320 Ω, the resistance of the fourth adjustable branch is R 13 = 710 Ω, the resistance of the fifth adjustable branch is R 14 = 190 Ω, the resistance of the sixth adjustable branch is R 15 =520 Ω; The resistor array contains 6 adjustable ranges; specifically, the first adjustable branch resistor is R. 10 = 1 kΩ, the resistance of the second adjustable branch is R 11 = 130 Ω, the resistance of the third adjustable branch is R 12 = 300 Ω, the resistance of the fourth adjustable branch is R 13 = 240 Ω, the resistance of the fifth adjustable branch is R 14 = 220 Ω, the resistance of the sixth adjustable branch is R 15 = 500Ω.

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