CN111064448A - Transconductance capacitance filter - Google Patents
Transconductance capacitance filter Download PDFInfo
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- CN111064448A CN111064448A CN202010021394.4A CN202010021394A CN111064448A CN 111064448 A CN111064448 A CN 111064448A CN 202010021394 A CN202010021394 A CN 202010021394A CN 111064448 A CN111064448 A CN 111064448A
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- transconductance
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- 239000003990 capacitor Substances 0.000 claims description 46
- 230000000295 complement effect Effects 0.000 claims description 5
- 238000007599 discharging Methods 0.000 claims description 2
- 238000001914 filtration Methods 0.000 claims 1
- 229920000729 poly(L-lysine) polymer Polymers 0.000 description 30
- 239000013256 coordination polymer Substances 0.000 description 3
- 239000013078 crystal Substances 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 238000000034 method Methods 0.000 description 3
- 230000000694 effects Effects 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
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- 238000011084 recovery Methods 0.000 description 1
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H11/00—Networks using active elements
- H03H11/02—Multiple-port networks
- H03H11/04—Frequency selective two-port networks
- H03H11/0422—Frequency selective two-port networks using transconductance amplifiers, e.g. gmC filters
- H03H11/0455—Multiple integrator loop feedback filters
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
- H03H11/00—Networks using active elements
- H03H11/02—Multiple-port networks
- H03H11/04—Frequency selective two-port networks
- H03H11/0422—Frequency selective two-port networks using transconductance amplifiers, e.g. gmC filters
- H03H11/0466—Filters combining transconductance amplifiers with other active elements, e.g. operational amplifiers, transistors, voltage conveyors
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- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
- H03L7/00—Automatic control of frequency or phase; Synchronisation
- H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
- H03L7/08—Details of the phase-locked loop
- H03L7/085—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal
- H03L7/087—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal using at least two phase detectors or a frequency and phase detector in the loop
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03L—AUTOMATIC CONTROL, STARTING, SYNCHRONISATION OR STABILISATION OF GENERATORS OF ELECTRONIC OSCILLATIONS OR PULSES
- H03L7/00—Automatic control of frequency or phase; Synchronisation
- H03L7/06—Automatic control of frequency or phase; Synchronisation using a reference signal applied to a frequency- or phase-locked loop
- H03L7/08—Details of the phase-locked loop
- H03L7/085—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal
- H03L7/093—Details of the phase-locked loop concerning mainly the frequency- or phase-detection arrangement including the filtering or amplification of its output signal using special filtering or amplification characteristics in the loop
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Abstract
The invention discloses a transconductance capacitance filter, which relates to the field of integrated circuits and comprises a constant Gm biasing circuit and a main filter, wherein the constant Gm biasing circuit outputs a control voltage Vct to the main filter. The constant Gm biasing circuit is adopted to replace an auxiliary PLL to bias a transconductance amplifier (OTA) in the filter, so that the area and power consumption are reduced, the signal-to-noise ratio of a signal path is increased, the mutual traction of locking clocks is avoided, and the frequency stability precision of the Gm-C filter is improved.
Description
Technical Field
The invention relates to the field of integrated circuits, in particular to a transconductance capacitance Gm-C filter.
Background
Existing large scale integrated active filters fall into roughly three categories, active RC filters, active MOSFET-C filters, and Gm-C filters (transconductance capacitance filters).
The active RC filter has an operational amplifier with a resistor and a capacitor on a feedback loop, and the operational amplifier must work in a low-frequency area with high loop gain to ensure enough precision. The active RC filter is not suitable for high frequency applications. Secondly, the filter adopts passive elements, the absolute accuracy of the passive elements is low, the absolute error can reach 15% to 20%, and the RC filter has no adjustable element, the only method is to use a resistor or a capacitor array, the circuit consumption area is large, and the tuning accuracy is limited. The active MOSFET-C filter is formed by replacing the resistor in the active RC filter with a MOSFET that operates in the linear region. By controlling the gate voltage of the MOSFET with the control voltage Vc, the resistance value and thus the frequency of the filter can be adjusted. Like the active RC filter, the active MOSFET-C filter is also suitable for lower frequencies, which requires that the equivalent resistance of the MOSFET is large while being in the linear region, resulting in a small variation range of Vc.
Compared with an active RC filter and an active MOSFET-C filter, the Gm-C filter can reach extremely high frequency, and the filter can be tuned in a wider frequency range and the frequency characteristic is accurate and stable by adjusting the Gm. The conventional tuning type Gm-C filter is tuned by an auxiliary PLL to stabilize the frequency characteristics. The basic idea is to construct a voltage controlled oscillator VCO in an auxiliary PLL with Gm (generated by a transconductance amplifier OTA) and a capacitor C of the same material, which is the same or proportional to the filter, and after the PLL loop is locked, the accuracy of the VCO output frequency Fvco is determined by the frequency accuracy of the external crystal oscillator. Meanwhile, the Fvco is Gm/2 pi C, the bias current of the OTA in the VCO is mirrored to the OTA in the filter, theoretically, the frequency characteristic of the filter is basically consistent with the output frequency characteristic of the auxiliary PLL, and the error source is only related to the mismatch of the Gm and the capacitor C.
However, the existing Gm-C filter has the following three disadvantages:
1. the auxiliary PLL circuit may cause large area and power consumption, increasing the complexity of the system.
2. The auxiliary PLL output lock frequency is in the same range as the filter frequency, the VCO output swing is usually large, and the signal is injected into the signal path, which reduces the signal-to-noise ratio of the signal path.
3. In systems where filters are present, there is usually a system master PLL, and if an auxiliary PLL is introduced, in systems with two PLLs there is a mutual pulling of the two locked clocks, reducing the purity of the output clocks to each other.
Therefore, those skilled in the art are dedicated to develop a transconductance-capacitor filter, which reduces area and power consumption, increases the signal-to-noise ratio of a signal path, avoids mutual pulling of locked clocks, and achieves the purpose of improving the frequency stability and accuracy of the Gm-C filter.
Disclosure of Invention
In view of the above-mentioned defects of the prior art, the technical problem to be solved by the present invention is how to reduce the area and power consumption, increase the signal-to-noise ratio of the signal path, avoid the mutual pulling of the lock clocks, and achieve the purpose of improving the frequency stability precision of the Gm-C filter.
In order to achieve the above purpose, the inventor finds that the improved constant Gm bias circuit is adopted to replace an auxiliary PLL, so that the matching of the capacitor is reasonably made, and the frequency stability characteristic of the filter can be higher. Thus, in one embodiment of the present invention, a transconductance-capacitive filter is provided that includes a constant Gm bias circuit that outputs a control voltage Vct to a main filter.
Optionally, in the transconductance capacitor filter in the above embodiment, the constant Gm bias circuit includes a PMOS transistor current mirror, a current mirror bypass capacitor, an NMOS transistor current mirror, and a switch capacitor, the PMOS transistor current mirror is connected to the NMOS transistor current mirror, the current mirror bypass capacitor is connected to the PMOS transistor current mirror to filter current noise of the PMOS transistor current mirror, and the switch capacitor is connected to the NMOS transistor current mirror.
Optionally, in the transconductance capacitor filter in any one of the embodiments above, the PMOS transistor current mirror includes a PMOS transistor one and a PMOS transistor two.
Optionally, in the transconductance capacitance filter in any one of the embodiments above, the NMOS transistor current mirror includes a first NMOS transistor and a second NMOS transistor.
Optionally, in the transconductance capacitance filter in any one of the embodiments above, drains of the PMOS transistor i and the PMOS transistor ii are connected to drains of the NMOS transistor i and the NMOS transistor ii, respectively.
Optionally, in the transconductance capacitance filter in any one of the embodiments, two sides of the switched capacitor are respectively connected to the source of the second NMOS transistor and ground.
Optionally, in the transconductance capacitance filter in any one of the above embodiments, the switched capacitance includes a pair of complementary switches CK and CK
A capacitor charged when CK is closed, when CK is closed
Discharging the capacitor when closed.
Further, in the transconductance capacitance filter in any one of the above embodiments, the switched capacitor is equivalent to a resistor and a resistance value
R＝(CsFck)-1(1)，
Wherein C issIs the capacitance value of the switched capacitor, FckIs the frequency of the switch control signal.
Further, in the transconductance capacitance filter in any one of the embodiments above, a transconductance of the NMOS transistor one
Wherein K is the ratio of the sizes of the NMOS tube II and the NMOS tube I, and the formula (1) is substituted to obtain
Further, in the transconductance capacitance filter in any one of the above embodiments, the current on the first NMOS transistor is copied to the main filter through the NMOS transistor current mirror, so that the internal transconductance of the main filter is enabled
Gm＝Gml (4)，
Obtained by substituting the formula (3)
(5)，
Wherein FckThe system of the main filterThe clock signal output by the PLL in the system is obtained by frequency division, and the complementary switch of the switched capacitor is controlled.
The main filter is typically integrated in a wireless or wired data transceiving system. In a wireless transceiver system, there is a local oscillator signal generated by a PLL, which is down-converted with a radio frequency signal to generate an intermediate frequency signal (wireless reception) or up-converted with an intermediate frequency signal to generate a radio frequency signal (wireless transmission). The switch control signal is obtained by frequency division of a local oscillator signal generated by the PLL, and the frequency of the local oscillator signal is Fck. In a wired data transceiving system, there is a method of generating a local clock signal by a CDR (clock and data recovery) circuit, and timing and recovering a received or transmitted data signal. The switch control signal is obtained by dividing the frequency of the local clock generated by the CDR by a frequency Fck。
In an embodiment of the present invention, the inventor provides a circuit including the transconductance capacitance filter of any one of the above embodiments.
The invention adopts a constant Gm bias circuit to replace a transconductance amplifier (OTA) in an auxiliary PLL de-bias filter. The constant Gm bias circuit consumes less area and consumes less power than the auxiliary PLL circuit. The switching signal of the switched capacitor is obtained by frequency division of the main PLL, the freedom degree of selection of the switching frequency is higher, the switching frequency is not necessarily in the passband frequency of the filter, and the signal-to-noise ratio of the filter is not reduced. Meanwhile, one PLL is reduced, the interference of extra frequency components to the main clock/main frequency is reduced, the risk of system operation is reduced, and the purity of the output frequency of the main PLL in the system is improved.
The conception, the specific structure and the technical effects of the present invention will be further described with reference to the accompanying drawings to fully understand the objects, the features and the effects of the present invention.
Drawings
Fig. 1 is a block diagram illustrating an auxiliary PLL tuned filter in accordance with an exemplary embodiment;
FIG. 2 is a block diagram illustrating a transconductance capacitance filter in accordance with an illustrative embodiment;
fig. 3 is a block diagram illustrating a circuit according to an example embodiment.
Detailed Description
The technical contents of the preferred embodiments of the present invention will be more clearly and easily understood by referring to the drawings attached to the specification. The present invention may be embodied in many different forms of embodiments and the scope of the invention is not limited to the embodiments set forth herein.
In the drawings, structurally identical elements are represented by like reference numerals, and structurally or functionally similar elements are represented by like reference numerals throughout the several views. The size and thickness of each component shown in the drawings are arbitrarily illustrated, and the present invention is not limited to the size and thickness of each component. The thickness of the components is exaggerated somewhat schematically and appropriately in order to make the illustration clearer.
As shown in fig. 1, a conventional auxiliary PLL tuning type filter includes an auxiliary PLL300 and a main filter 301, the auxiliary PLL300 includes a Phase Frequency Detector (PFD)302, a Charge Pump (CP)303, a Low Pass Filter (LPF)304 and a Voltage Controlled Oscillator (VCO)305, and the main filter 301 includes a main filter transconductance 100 and a main filter integrating capacitor 101. The Voltage Controlled Oscillator (VCO)305 is formed by N stages of Gm-C integrators through positive feedback, parameters of the Gm-C integrators of each stage are the same, that is, parameters of the transconductance 200 and the capacitor 201 are the same, Fout is Gm/2 pi NC, where Fout is an output signal frequency of the Voltage Controlled Oscillator (VCO), Gm is a transconductance of each stage of a transconductance amplifier (OTA) inside the VCO, N is a stage number of the Gm-C integrators, and C is a total capacitance of an output node of the transconductance amplifier (OTA). The Fin input frequency is generated by an external crystal oscillator of the chip. The Phase Frequency Detector (PFD)302 exclusive-ors the Fin and Fout signals, compares the frequency and phase differences of the two signals, outputs the difference signal to control the charge pump CP, and after the output signal of the Charge Pump (CP)303 passes through the Low Pass Filter (LPF)304, generates the control voltage Vct of the Voltage Controlled Oscillator (VCO)305, which changes the frequency of the VCO by changing the Gm of the transconductance amplifier (OTA). Vct is simultaneously connected to Gm transconductance amplifier 100 in main filter 301, so that transconductance amplifier 100 of the main filter changes synchronously with Gm of the transconductance amplifier of the VCO. When the auxiliary PLL is locked, Fout is Fin, since Fin is generated by an external crystal oscillator of a chip, the frequency stability is extremely high, and the aim of stabilizing the Gm-C filter is achieved. Meanwhile, the frequency characteristic of the main filter is also determined by Gm-C, so that the frequency characteristic of the main filter is stabilized. However, the Gm-C filter has the following three disadvantages:
1. the auxiliary PLL circuit may cause large area and power consumption, increasing the complexity of the system.
2. The auxiliary PLL output lock frequency is in the same range as the filter frequency, the VCO output swing is usually large, and the signal is injected into the signal path, which reduces the signal-to-noise ratio of the signal path.
3. In systems where filters are present, there is usually a system master PLL, and if an auxiliary PLL is introduced, in systems with two PLLs there is a mutual pulling of the two locked clocks, reducing the purity of the output clocks to each other.
The inventor finds that the improved constant Gm bias circuit is adopted to replace an auxiliary PLL, so that the matching of the capacitor is reasonably made, and the high frequency stability characteristic of the filter can be obtained.
As shown in fig. 2, a transconductance capacitance filter according to an embodiment of the present invention includes a constant Gm bias circuit 400 and a main filter 301, and the constant Gm bias circuit 400 outputs a control voltage Vct to the main filter 301. The constant Gm bias circuit 400 comprises a PMOS tube current mirror, a current mirror bypass capacitor 408, an NMOS tube current mirror and a switch capacitor, wherein the PMOS tube current mirror is connected with the NMOS tube current mirror, the current mirror bypass capacitor 408 is connected with the PMOS tube current mirror to filter current noise of the MOS tube current mirror, and the switch capacitor is connected with the NMOS tube current mirror; the PMOS tube current mirror comprises a PMOS tube I401 and a PMOS tube II 402, the NMOS tube current mirror comprises an NMOS tube I403 and an NMOS tube II 404, and drain electrodes of the PMOS tube I401 and the PMOS tube II 402 are respectively connected with drain electrodes of the NMOS tube I403 and the NMOS tube II 404; the source electrode of the NMOS tube II 404 and the ground are respectively connected to two sides of a switched capacitor, and the switched capacitor comprises a pair of complementary switches CK405 and CK
406. A capacitor 407, wherein the capacitor 407 is charged when CK405 is closed, and when CK405 is closed
406 are closed to discharge capacitor 407. The inventor equates the switched capacitor to a resistor and calculates the resistance as follows:
R＝(CsFck)-1(1),
wherein C issIs the capacitance value of the switched capacitor, FckIs the frequency of the switch control signal.
Calculating transconductance of the NMOS transistor one 403:
where K is the ratio of the sizes of the NMOS transistor II 404 and the NMOS transistor I403, and the formula (1) is substituted to obtain
Copying the current on the NMOS transistor I403 to the main filter 301 through the NMOS transistor current mirror to make the internal transconductance of the main filter 301 equal to that of the NMOS transistor I403
Gm＝Gml (4)，
Obtained by substituting the formula (3)
Wherein FckThe frequency division is obtained by the clock signal output by the PLL in the system where the main filter is located, the complementary switch of the switch capacitor is controlled, extra PLL is not needed, and the frequency stability and the precision are high; the frequency characteristics of the main filter are:
through reasonable matching, the K value can be higher in precision and does not change along with PVT (process, voltage and temperature) conditions. The ratio of the switched capacitor to the main filter integrating capacitor 101 can also be made to a higher accuracy. It can be seen from this that the frequency characteristics of the filter can be stabilized well by performing bias control and tuning of the filter by the constant Gm bias instead of the auxiliary PLL.
As shown in fig. 3, a circuit 10000 includes a transconductance capacitance filter 11601 of the above-described embodiment of the present invention in the structure.
The foregoing detailed description of the preferred embodiments of the invention has been presented. It should be understood that numerous modifications and variations could be devised by those skilled in the art in light of the present teachings without departing from the inventive concepts. Therefore, the technical solutions available to those skilled in the art through logic analysis, reasoning and limited experiments based on the prior art according to the concept of the present invention should be within the scope of protection defined by the claims.
Claims (10)
1. A transconductance capacitance filter, comprising a constant Gm bias circuit and a main filter, the constant Gm bias circuit outputting a control voltage Vct to the main filter.
2. The transconductance capacitance filter of claim 1, wherein said constant Gm bias circuit comprises a PMOS transistor current mirror, a current mirror bypass capacitor, an NMOS transistor current mirror, and a switch capacitor, said PMOS transistor current mirror and said NMOS transistor current mirror being connected, said current mirror bypass capacitor being connected to said PMOS transistor current mirror for filtering current noise of said PMOS transistor current mirror, said switch capacitor being connected to said NMOS transistor current mirror.
3. The transconductance capacitance filter of claim 2, wherein said PMOS transistor current mirror includes a PMOS transistor one and a PMOS transistor two.
4. The transconductance capacitance filter of claim 3, wherein said NMOS transistor current mirror includes NMOS transistor one and NMOS transistor two.
5. The transconductance capacitance filter of claim 4, wherein drains of said first PMOS transistor and said second PMOS transistor are connected to drains of said first NMOS transistor and said second NMOS transistor, respectively.
6. The transconductance capacitance filter of claim 5, wherein two sides of said switch capacitor are connected to the source of said second NMOS transistor and ground, respectively.
7. A transconductance capacitance filter according to any one of claims 2 to 6, characterized in that said switched capacitance comprises a pair of complementary switches CK and CK
A capacitor charged when CK is closed, when CK is closed
Discharging the capacitor when closed.
8. The transconductor-capacitor filter as claimed in claim 7, wherein the switched capacitor is equivalent to a resistor with a resistance of (R ═ C)sFck)-1In which C issIs the capacitance value of the switched capacitor, FckIs the frequency of the switch control signal.
9. The transconductance capacitance filter of claim 8, wherein an internal transconductance of said main filter copies a current on said NMOS transistor to said main filter through said NMOS transistor current mirror
Wherein FckAnd K is the ratio of the sizes of the second NMOS transistor and the first NMOS transistor.
10. A circuit comprising a transconductance capacitance filter according to any one of claims 1-9.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202010021394.4A CN111064448A (en) | 2020-01-09 | 2020-01-09 | Transconductance capacitance filter |
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| Application Number | Priority Date | Filing Date | Title |
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| CN202010021394.4A CN111064448A (en) | 2020-01-09 | 2020-01-09 | Transconductance capacitance filter |
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Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20020163384A1 (en) * | 2001-03-14 | 2002-11-07 | Yasumasa Hasegawa | Transconductor and filter circuit using the same |
| CN101588164A (en) * | 2009-06-18 | 2009-11-25 | 中国科学院微电子研究所 | A kind of constant transconductance biasing circuit |
| JP2011082825A (en) * | 2009-10-07 | 2011-04-21 | Asahi Kasei Electronics Co Ltd | Filter circuit |
| US20120025899A1 (en) * | 2010-07-30 | 2012-02-02 | Tialinx, Inc. | Tunable transconductance-capacitance filter with coefficients independent of variations in process corner, temperature, and input supply voltage |
| CN104660216A (en) * | 2015-03-02 | 2015-05-27 | 东南大学 | High-precision frequency calibration circuit for Gm-C filter |
| CN211063586U (en) * | 2020-01-09 | 2020-07-21 | 宁波爱芯微电子有限公司 | Transconductance capacitance filter and circuit |
-
2020
- 2020-01-09 CN CN202010021394.4A patent/CN111064448A/en active Pending
Patent Citations (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20020163384A1 (en) * | 2001-03-14 | 2002-11-07 | Yasumasa Hasegawa | Transconductor and filter circuit using the same |
| CN101588164A (en) * | 2009-06-18 | 2009-11-25 | 中国科学院微电子研究所 | A kind of constant transconductance biasing circuit |
| JP2011082825A (en) * | 2009-10-07 | 2011-04-21 | Asahi Kasei Electronics Co Ltd | Filter circuit |
| US20120025899A1 (en) * | 2010-07-30 | 2012-02-02 | Tialinx, Inc. | Tunable transconductance-capacitance filter with coefficients independent of variations in process corner, temperature, and input supply voltage |
| CN104660216A (en) * | 2015-03-02 | 2015-05-27 | 东南大学 | High-precision frequency calibration circuit for Gm-C filter |
| CN211063586U (en) * | 2020-01-09 | 2020-07-21 | 宁波爱芯微电子有限公司 | Transconductance capacitance filter and circuit |
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