CN211063586U

CN211063586U - Transconductance capacitance filter and circuit

Info

Publication number: CN211063586U
Application number: CN202020045008.0U
Authority: CN
Inventors: 李富民; 童红杰
Original assignee: Ningbo Aixin Microelectronics Co ltd
Current assignee: Ningbo Aixin Microelectronics Co ltd
Priority date: 2020-01-09
Filing date: 2020-01-09
Publication date: 2020-07-21
Anticipated expiration: 2030-01-09

Abstract

The utility model discloses a transconductance capacitance filter relates to the integrated circuit field, including invariable Gm biasing circuit and main filter, invariable Gm biasing circuit output control voltage Vct to main filter the utility model also discloses a transconductance capacitance filter circuit, including above-mentioned transconductance capacitance filter, the utility model discloses an adopt invariable Gm biasing circuit to replace supplementary P LL to go the inside transconductance amplifier (OTA) of biasing filter, reduced area and power consumption, increased signal path's SNR, avoided pulling mutually of locking the clock, improved Gm-C filter's frequency stability precision.

Description

Transconductance capacitance filter and circuit

Technical Field

The utility model relates to an integrated circuit field especially relates to a transconductance capacitance filter and circuit.

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 the MOSFET to have a large equivalent resistance while being in the linear region, resulting in a small variation range of Vc.

The basic idea is to use Gm (generated by a transconductance amplifier OTA) and a capacitor C of the same material, which are the same or proportional to the filter, to construct a voltage controlled oscillator VCO in the auxiliary P LL, and after the P LL loop is locked, the accuracy of the output frequency Fvco of the VCO is determined by the frequency accuracy of the external crystal oscillator, and at the same time, Fvco Gm/2 pi C mirrors the bias current of the OTA in the VCO to the OTA in the filter, theoretically, the frequency characteristic of the filter is substantially consistent with the output frequency characteristic of the auxiliary P LL, and the error source is only related to the mismatch of Gm and capacitor C.

However, the existing Gm-C filter has the following three disadvantages:

1. the auxiliary P LL circuit results in larger area and power consumption, increasing the complexity of the system.

2. The auxiliary P LL 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 P LL, and if an auxiliary P LL is introduced, in two P LL systems there is mutual pulling of the two locked clocks, reducing the purity of each other's output clocks.

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.

SUMMERY OF THE UTILITY MODEL

In view of the above-mentioned defects in the prior art, the technical problem to be solved in 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 clock, and achieve the purpose of improving the frequency stability precision of the Gm-C filter.

Accordingly, in one embodiment of the present invention, a transconductance capacitance filter is provided, comprising a constant Gm bias circuit and a main filter, wherein the constant Gm bias circuit outputs a control voltage Vct to the 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＝(C_sF_ck)^-1(1)，

Wherein C is_sIs the capacitance value of the switched capacitor, F_ckIs 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, the air conditioner is provided with a fan,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 G of the main filter is enabled_m＝G_m1 and 4, obtained by substituting the formula (3)

Wherein F_ckThe clock signal output by P LL in the system of the main filter is divided to control the complementary switch of the switch capacitor.

In a wireless transceiver system, there is a local oscillator signal generated by P LL, 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)_ck. 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 F_ck。

In an embodiment of the present invention, a circuit is provided, which includes the transconductance capacitance filter of any one of the embodiments.

The utility model discloses a invariable Gm biasing circuit replaces supplementary P LL to go the transconductance amplifier (OTA) of biasing wave filter inside comparing with supplementary P LL circuit, the area that invariable Gm biasing circuit consumed is littleer, the consumption is lower the switched-capacitor's switched signal obtains by main P LL frequency division, switching frequency's selection degree of freedom is higher, it is inside not necessarily to be in the passband frequency of wave filter, can not reduce the SNR of wave filter, and simultaneously, reduce a P LL, the interference of extra frequency component to main clock/dominant frequency has been reduced, the risk of system operation has been reduced, the purity of main P LL output frequency in the system has been improved.

The conception, the specific structure and the technical effects of the present invention will be further described with reference to the accompanying drawings, so as to fully understand the objects, the features and the effects of the present invention.

Drawings

FIG. 1 is a block diagram illustrating an auxiliary P LL 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 understood and appreciated 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 described 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 P LL tuned filter includes an auxiliary P LL and a main filter 301, the auxiliary P LL includes a Phase Frequency Detector (PFD)302, a Charge Pump (CP)303, a low pass filter (L PF)304 and a Voltage Controlled Oscillator (VCO)305, the main filter 301 includes a main filter transconductance 100 and a main filter integrating capacitor 101, the Voltage Controlled Oscillator (VCO)305 is composed of N stages of Gm-C integrators through positive feedback, parameters of the Gm-C integrators of each stage are the same, i.e., parameters of transconductance 200 and capacitor 201 are the same, Fout is Gm/2 NC, where Fout is the frequency of an output signal of the Voltage Controlled Oscillator (VCO), Gm is the transconductance of a transconductance amplifier (OTA) inside each stage, N is the stage of the Gm-C integrator, C is the total capacitance of an output node of the transconductance amplifier (OTA), Fin input frequency is generated by an external crystal oscillator (PFD), Fin and a signal are xored, phase difference of the signal and the transconductance signal is compared with the voltage of the main oscillator (VCO) output node, the transconductance amplifier (VCO) 200, Fout is generated by an external crystal oscillator (VCO), the external crystal oscillator (VCO) which generates a stable frequency detector (VCO), the VCO) generates a stable frequency detector (VCO), the stable oscillator (VCO) generates a stable oscillator (VCO) according to the frequency detector (VCO), the voltage of the voltage detector (VCO) generates a stable oscillator (VCO) 100, the stable oscillator (VCO) when the frequency detector (VCO) generates a stable oscillator (VCO), the stable oscillator (VCO) outputs a stable oscillator (VCO), the stable oscillator (VCO) generates a stable frequency detector (VCO), the stable oscillator (VCO) generates a stable oscillator (VCO), the stable oscillator (VCO) generates a stable frequency detector (VCO), the stable oscillator (VCO) generates a stable oscillator (VCO), the stable oscillator (VCO) generates a stable frequency:

The inventor finds that the improved constant Gm bias circuit is adopted to replace the auxiliary P LL, the matching of the capacitance 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, wherein 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, and the NMOS tube current mirror comprises an NMOS tube I403 and an NMOS tube N402The drain electrodes of the PMOS tube I401 and the PMOS tube II 402 are respectively connected with the 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

A capacitor 407, wherein the capacitor 407 is charged when CK405 is closed, and when CK405 is closed

When closed, discharges capacitor 407. The inventor equates the switched capacitor to a resistor and calculates the resistance as follows:

R＝(C_sF_ck)^-1(1)，

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

G_m＝G_m1 (4)，

Obtained by substituting the formula (3)

Wherein F_ckClock output by P LL in system in which the main filter is locatedThe frequency division of the signal is obtained, the complementary switch of the switch capacitor is controlled, no extra P LL is needed, the frequency stability and the precision are high, and the frequency characteristic of the main filter is as follows:

the K value can be accurately obtained through reasonable matching and does not change along with PVT (process, voltage and temperature) conditions, and the proportion of the switch capacitor and the main filter integrating capacitor 101 can also be accurately obtained.

As shown in fig. 3, a circuit 10000 includes a transconductance capacitance filter 11601 of the embodiment of the present invention in the structure.

The foregoing has described in detail preferred embodiments of the present invention. It should be understood that numerous modifications and variations can be devised by those skilled in the art in light of the teachings of the present invention without undue experimentation. Therefore, the technical solutions that can be obtained by a person skilled in the art through logic analysis, reasoning or limited experiments based on the prior art according to the concepts of the present invention should be within the scope of protection defined by the claims.

Claims

1. The utility model provides a transconductance capacitance filter, its characterized in that, includes invariable Gm bias circuit and main filter, invariable Gm bias circuit output control voltage Vct arrives main filter, invariable Gm bias circuit includes PMOS pipe current mirror, current mirror bypass capacitance, NMOS pipe current mirror and switch capacitance, PMOS pipe current mirror with NMOS pipe current mirror connects, current mirror bypass capacitance connects PMOS pipe current mirror, filters the current noise of PMOS pipe current mirror, switch capacitance connects NMOS pipe current mirror.

2. The transconductance capacitance filter of claim 1, wherein said PMOS transistor current mirror includes a PMOS transistor one and a PMOS transistor two.

3. The transconductance capacitance filter of claim 2, wherein said NMOS transistor current mirror includes NMOS transistor one and NMOS transistor two.

4. The transconductance capacitance filter of claim 3, 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.

5. The transconductance capacitance filter of claim 4, wherein two sides of said switch capacitor are connected to the source of said second NMOS transistor and ground, respectively.

6. A transconductance capacitance filter according to any one of claims 1 to 5, 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.

7. A circuit comprising a transconductance capacitance filter according to any one of claims 1-6.