WO2001029981A1

WO2001029981A1 - Wireless transceivers using two integrated filters to enhanc e dynamic range

Info

Publication number: WO2001029981A1
Application number: PCT/US2000/041375
Authority: WO
Inventors: Bernard C. Duggan; James R. Smillie
Original assignee: Maxim Integrated Products, Inc.
Priority date: 1999-10-20
Filing date: 2000-10-20
Publication date: 2001-04-26
Also published as: WO2001029978A1

Abstract

A monolithic wireless transceiver integrated circuit of the present invention includes an internal RLC filter (204) and an internal bandpass filter (206) coupled to the internal RLC filter (204). The use of internal IF filters by the present invention substantially reduces power dissipation caused from IF signals off chip using external IF filters. In addition, the present invention improves IC form factor and fabrication cost by eliminating the need for external IF filters which are typically made of materials beyond the capabilities of conventional low-power integrated filter technologies. Moreover, the present invention increases the dynamic range of an internal filter configuration to greater than 80dB.

Description

WIRELESS TRANSCEIVERS USING TWO INTEGRATED FILTERS TO ENHANCE

DYNAMIC RANGE

Description

Technical Field

The present invention relates to wireless transceiver systems. In particular, the present invention teaches a receiver integrated circuit architecture utilizing monolithic receiver filters. Among other advantages, the use of monolithic, or internal, receiver filters eliminates the need for external placement of receiver filters from wireless transceiver systems.

Background Art

The portable communications revolution is upon us today. It promises to empower individuals throughout the world by giving them low-cost access to information wherever they may be, thus allowing them to make informed decisions and to be more productive in business and at home, without necessarily being tied down to a physical location.

Were it not for the advent of the portable communications revolution, radio technique would almost certainly become a lost art. Radio communication methods, at least for nonmilitary applications, have remained relatively unchanged since World War π, and the evolutionary improvements in consumer equipment mainly owes to the use of high-frequency discrete transistors, smaller passive components, and building block integrated circuits which improve the long term reliability and manufacturability of radio and TV receivers. However, front-end radio architectures have evolved almost not at all. For example, integrated circuits have contributed digital volume-control, digital frequency-tuning, features to alleviate manual effort on the part of the user, but the RF and IF sections still contain discrete and passive components in rather conventional architectures.

To set the stage for further discussion, some of the unique problems of radio receivers and transmitters must be described. Unlike familiar wireline communications, the wireless environment accommodates essentially an unlimited number of users sharing different parts of the spectrum. As a consequence of this spectrum sharing, very strong signals often coexist next to very weak signals. The radio receiver must be able to select the signal of interest, while rejecting all others, and it must do so using less than perfect active and passive components. One important problem in receiver design is image-rejection. Image-rejection relates to the receiver's ability to select the desired signal from the array of signals occupying the spectrum. Ideally, this would be done with a tunable bandpass filter, whose center frequency could be positioned at will in the RF, and whose passband was one channel wide. However, a filter with this small a fractional passband does not exist. Instead, a conventional RF bandpass filter, which may or may not be tunable, will preselect an array of radio channels including the one of interest. The other preselected channels are then removed at a lower intermediate-frequency (IF), by translating them in frequency with a downconversion mixer, and centering the desired channel within a bandpass filter at IF. The other mixer input is a frequency-tunable local oscillator (LO), offset by IF from the desired channel. As the preselected band after downconversion will very likely occupy an interval greater than (0, IF) on the frequency-axis, the IF bandpass filter will select both the desired channel, and another image channel the mixer has translated to -IF. The subsequent detector circuit will be unable to distinguish between the desired and the image channels, and therefore its output will be the result of the superposition of both. However, if the stopband of the preselect filter lies less than 2 x IF away from the desired channel it will attenuate the image, so only the desired channel will contribute energy at IF. A high IF relaxes the prefilter passband specification, but it also means that the downconverted signal requires high-frequency amplifiers, which are usually power-inefficient. Further, the IF filter requires a smaller fractional passband. In such cases, following image rejection at this high IF, the channel may be selected after downconversion to a second, lower IF. In such a receiver, the first IF may actually lie at a higher frequency than the incoming RF to make image rejection easier.

As requirements for reduced receiver size increase, efforts to eliminate off-chip passive components grow. However, certain passive inductors, capacitors, and resistors can not be eliminated or scaled down. Thus, they conventionally remain off-chip. Prior Art Figure 1 is a block diagram of a prior art transceiver 100, including a transceiver integrated circuit (IC) 102, external RLC filters 104 coupled to the transceiver IC 102, and an external bandpass filter (BPF) 106 coupled to the external RLC filters 104 and the transceiver IC 102. As discussed above, the RLC filters 104 and BPF are conventionally external to the transceiver IC because of scaling difficulties with this transceiver components. Moreover, the RLC 104 and BPF are both required to meet the flat band response and the group delay performance.

Conventional transceivers require a high-Q, low-noise, low-distortion bandpass IF filter which is well beyond the capabilities of conventional low-power integrated filter technologies. As a result, external high-Q passive filters are generally used, as shown in Prior Art Figure 1. Typically these filters are SAW filters, ceramic filters, or LC filters. Because of the frequencies involved and the package parasitics usually present, considerable power dissipation is involved in taking IF signals off chip into these devices. Moreover, even if internal filters are utilized, they conventionally only allow a dynamic range of about 65dB. But, WLAN requires a dynamic range of greater than 80dB.

Accordingly, there exist a need for improved integration of RF transceivers, with resulting further improvements in power dissipation, form factor, and cost. Furthermore, there exist a need for an internal filter configuration having a dynamic range much higher than 65dB, which is the conventional maximum.

Summary of the Invention

The present inventions meets the aforementioned needs by providing a monolithic wireless transceiver having integrated IF filters for RX and TX. The present invention replaces the external filters with an internal RLC gyrator filter and an internal bandpass filter (BPF).

In one embodiment of the present invention, a wireless receiver integrated circuit having internal IF filters for RX is disclosed. In this embodiment, an RLC filter internal to the integrated circuit is coupled with an internal BPF. The internal configuration of the IF filters prevent power dissipation by having higher impedance levels. Moreover, the configuration of the IF filters further increases the dynamic range to greater than 65dB, which is the maximum IF dynamic range under conventional practices.

In another embodiment, a wireless receiver integrated circuit including an internal means for filtering IF signals is disclosed. The wireless receiver includes a first internal filter means for reducing a level of interfering signals, and a second internal filter means for further reducing interfering signals. The first and second filters means are configured on the wireless receiver integrated circuit such that the first filter means reduces the level of interfering signals to within a dynamic range of the second filter.

In yet another embodiment, the invention relates to a wireless transceiver integrated circuit having a transmitter, and a wireless receiver having internal IF filters. The wireless receiver includes an internal RLC gyrator filter, and an internal BPF coupled to the RLC gyrator filter. The internal RLC gyrator filter allows the IF of the present invention to have a dynamic range greater than 80dB.

To achieve the dynamic range enhancement required by wireless transceivers using internal filters, the RLC filter is used to limit the wanted signal. The RLC also suppresses the unwanted signal to protect the complex BPF from being overdriven by a signal which would allow for the filter to remain within its linear operating region.

These unwanted signals in the RLC must not cause any distortion when suppressed. This is achieved by driving current into a parallel RLC filter. The Q of this filter is set to achieve the dynamic range enhancement required in the BPF. The RLC also equalizes the Group Delay of the BPF to achieve the system requirements of 4L-FSK.

Brief Description of the Drawings These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following descriptions and a study of the various figures of the drawings, wherein:

Prior Art Figure 1 is a schematic diagram of a wireless transceiver architecture requiring external bandpass filters (BPFs);

Figure 2 is a schematic diagram of a wireless receiver filter architecture utilizing monolithic receiver filters in accordance with one embodiment of the present invention;

Figure 3a is a schematic diagram showing a theoretical equivalent passive RLC filter of the RLC gyrator filter of Figure 2;

Figure 3b is a schematic diagram showing one suitable internal RLC gyrator filter in accordance with another embodiment of the present invention;

Figure 4 is a schematic diagram illustrating a 2.4 GHz ISM wireless receiver architecture in accordance with yet another embodiment of the present invention;

Figure 5 is a graph showing the frequency response of the internal RLC gyrator filter utilized by one embodiment of the present invention;

Figure 6 is a graph showing the group delay of the internal Butterworth BPF, the internal RLC gyrator filter, and the overall group delay of another embodiment of the present invention; and

Figure 7 is a graph showing the attenuation of the combined internal RLC gyrator filter and the internal Butterworth BPF in accordance with one aspect of the present invention. Disclosure of the Invention

Prior Art Figure 1 was discussed in terms of the prior art. A preferred embodiment of the present invention will now be described with reference to Figure 2. Figure 2 is a schematic diagram of a wireless receiver channel rejection filter architecture 200 in accordance with one embodiment of the present invention. The wireless receiver architecture 200 includes a GM amplifier 202, an internal RLC gyrator filter 204, and an internal BPF 206. The internal RLC gyrator 204 is coupled to the GM amplifier 202, and the internal BPF 206 is coupled to the RLC gyrator 204.

The IF signal is received by the GM amplifier 202 and then passed on to the internal RLC gyrator filter 204. The internal RLC gyrator filter 204 is utilized to reduce the level of interfering signals to within a dynamic range operable by the internal BPF 206. The internal BPF 206 is then utilized to further reduce the interfering signals within the IF signal before the IF signal is passed onto a limiter. Previously it was considered that both the RLC filter and the BPF had to have a flat gain response (ldB points @ +/-lMHz). However, this criteria was eliminated in the present invention by utilizing the internal RLC gyrator filter 204 and a subsequent limiter, which compensates for any gain variations caused by the active components. For in-band signals the Gm-RLC is overdriven by 15dB, which does not have any substantial detrimental effect apart from limited RSSI loss of range.

Figure 3a is a schematic diagram showing a passive theoretical equivalent conventional passive RLC filter of the RLC gyrator filter of Figure 2. The conventional passive RLC filter 300 includes a resistor 302, an inductor 304, and a capacitor 306 all coupled in parallel. It should be borne in mind that the conventional passive RLC filter 300 typically cannot be integrated.

Turning next to Figure 3b, a schematic diagram showing one possible realization of the internal RLC gyrator filter 204 of Figure 2 in accordance with one embodiment of the present invention is shown. The internal RLC gyrator filter 204 performs essentially the same function as the conventional passive RLC filter 300. However, the RLC gyrator filter 204 utilized in the present invention can be integrated into a wireless receiver IC using gyrator techniques. The internal RLC gyrator may take the form of a resistor 308, a first capacitor 310 coupled in parallel with the resistor 308, a second capacitor 312 coupled in parallel with the first capacitor 310, and a gyrator 314 coupled in series with the first capacitor 310 and the second capacitor 312. The gyrator 314 serially coupled between the first capacitor 310 and the second capacitor 312 allows the IF of the wireless receiver to have a dynamic range that is greater than 80dB even though the BPF has a dynamic range of only 65dB.

Figure 4 is a schematic diagram illustrating a 2.4 GHz ISM receiver architecture 400 in accordance with yet another embodiment of the present invention. The wireless receiver architecture 400 includes an image reject downconverter 402, an internal RLC gyrator 204 coupled to the image reject downconverter 402, an internal RX 5^th order Butterworth BPF 206 coupled to the internal RLC gyrator 204, a limiter 404 coupled to the Butterworth BPF 206, a lowpass filter (LPF) coupled to the limiter 404, and an output buffer 408 coupled to the LPF 406. The internal RLC gyrator 204 includes a first amplifier 410 coupled to the image reject downconverter 402, and a first BPF 412 coupled to the first amplifier 410. The butterworth BPF 206 includes a second amplifier 414 coupled to the first BPF 412, and a second BPF coupled to the second amplifier 414 and the limiter 404.

The internal RLC gyrator filter 204 and subsequent limiter compensates for any gain variations. For in-band signals the first amplifier 410 is overdriven by 15dB, which does not have any substantial detrimental effect apart from limited range lost from the reduction of the RSSI range.

The electrical characteristics of the monolithic filters of the ISM receiver architecture 400 of Figure 4 are shown in Figures 5-9. Figure 5 is a graph showing the frequency response of the internal RLC gyrator filter utilized by the present invention. The graph illustrates the high selectivity of the internal RLC gyrator filter at the desired frequency of 5MHz. As can be seen from the graph, the impedance is highest at the desired frequency of 5MHz and drops off sharply at other frequencies. The effect the internal RLC gyrator filter has on the group delay is shown in Figure 6.

Figure 6 is a graph showing the group delay of the internal Butterworth BPF, the internal

RLC gyrator filter, and the overall group delay. As shown in the graph, the group delay of the internal Butterworth BPF 602 is opposed by the group delay of the internal RLC gyrator filter 604. The result is an overall group delay 606 which is essentially linear around the desired frequency.

Figure 7 is a graph showing the attenuation of the combined internal RLC gyrator filter and the internal Butterworth BPF. As can be seen from the graph, the dB attenuation tends toward zero at the desired frequency of 5MHz. Although only a few embodiments of the present invention have been described in detail herein, it should be understood that the present invention could be embodied in many other specific forms without departing from the spirit or scope of the invention.

Therefore, the present examples and embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope of the appended claims.

Claims

Claims I claim:

1. A wireless receiver formed at least in part on an integrated circuit, the wireless receiver comprising: an RLC filter that is internal to the integrated circuit; and a bandpass filter (BPF) that is internal to the integrated circuit, the internal BPF being coupled with the internal RLC filter, wherein the internal filters are configured so as to achieve a dynamic range greater than 80dB.

2. A wireless receiver as recited in claim 1 , wherein the internal RLC filter is a RLC gyrator filter.

3. A wireless receiver as recited in claim 1 , further comprising an internal limiter coupled with the internal bandpass filter.

4. A wireless receiver as recited in claim 3, further comprising an internal lowpass filter coupled with the internal limiter filter.

5. A wireless receiver as recited in claim 1, wherein a group delay ripple of the RLC filter and the bandpass filter suitable for 4L-FSK is less than 150nS.

6. A wireless receiver as recited in claim 1 , wherein the wireless receiver has an I.F. dynamic range that is greater than 80dB.

7. A wireless receiver as recited in claim 1 , wherein the wireless receiver has an I.F. dynamic range that is greater than 85dB.

8. A wireless receiver as recited in claim 7, wherein the RLC filter generates a negative phase delay ripple, the RLC filter configured such that the RLC negative phase delay ripple acts as an equalizer for the BPF phase ripple.

9. A wireless receiver as recited in claim 1 , wherein the RLC filter is overdriven by 15dB.

10. A wireless receiver as recited in claim 1, wherein the wireless receiver is one component of a transceiver formed at least in part on the integrated circuit.

11. A wireless receiver as recited in claim 1 , wherein the wireless receiver is suitable for FHSS applications utilizing a 2.4GHz Industrial, Scientific, and Medical (ISM) frequency band.

12. A wireless receiver as recited in claim 1, wherein the wireless receiver is operable on a UHF band.

13. A wireless receiver as recited in claim 1 , wherein the wireless receiver is suitable for use in a cellular phone.

14. A wireless receiver as recited in claim 1, wherein the wireless receiver is suitable for use in a digital phone.

15. A wireless receiver as recited in claim 1, wherein the wireless receiver is suitable for use in a wireless radio.

16. A wireless receiver as recited in claim 10, wherein the transceiver is operable as a WLAN transceiver utilizing a 2.5GHz frequency band.

17. A wireless receiver as recited in claim 1, wherein the internal filters are configured so as to achieve a dynamic range greater than 70dB.

18. A wireless receiver as recited in claim 1, wherein the internal filters are configured so as to achieve a dynamic range greater than 80dB.

19. A wireless receiver formed at least in part on an integrated circuit, the wireless receiver comprising: a first filter means for reducing a level of interfering signals, wherein the first filter means is internal to the integrated circuit; and a second filter means for further reducing the level of the interfering signals, wherein the second filter means is internal to the integrated circuit, wherein the first filter means reduces the level of interfering signals to within a dynamic range of the second filter means.

20. A wireless receiver as recited in claim 19, wherein the first filter means is a RLC gyrator filter.

21. A wireless receiver as recited in claim 19, further comprising an limiter means for compensating for gain variations from the first filter means and the second filter means, the limiter means being coupled with the second filter means.

22. A wireless receiver as recited in claim 21, further comprising an intemal third filter means for further reducing gain variations from the internal limiter means, the third filter means being coupled with the limiter means.

23. A wireless receiver as recited in claim 19, wherein a group delay ripple of the first filter means and the second filter means is less than 150nS.

24. A wireless receiver as recited in claim 19, wherein the wireless receiver has an I.F. dynamic range that is greater than 80dB.

25. A wireless receiver as recited in claim 19, wherein the wireless receiver has an I.F. dynamic range that is greater than 85dB.

26. A wireless receiver as recited in claim 25, wherein the first filter means generates a negative phase delay ripple, the first filter means configured such that the negative phase delay ripple acts as an equalizer for the second filter phase ripple.

27. A wireless receiver as recited in claim 19, wherein the first filter means is overdriven by 15dB.

28. A wireless receiver as recited in claim 19, wherein the wireless receiver is one component of a transceiver formed at least in part on the integrated circuit.

29. A wireless receiver as recited in claim 19, wherein the wireless receiver is suitable for FHSS applications utilizing a 2.4GHz Industrial, Scientific, and Medical (ISM) frequency band.

30. A wireless receiver as recited in claim 19, wherein the wireless receiver is operable on a UHF band.

31. A wireless receiver as recited in claim 19, wherein the wireless receiver is suitable for use in a cellular phone.

32. A wireless receiver as recited in claim 19, wherein the wireless receiver is suitable for use in a digital phone.

33. A wireless receiver as recited in claim 19, wherein the wireless receiver is suitable for use in a wireless radio.

34. A wireless receiver as recited in claim 28, wherein the transceiver is operable as a WLAN transceiver utilizing a 2.5GHz frequency band.

35. A wireless transceiver, comprising: a transmitter; and a wireless receiver formed at least in part on an integrated circuit, the wireless receiver including: an RLC gyrator filter that is internal to the integrated circuit; and a bandpass filter (BPF) that is internal to the integrated circuit, the internal

BPF being coupled with the internal RLC gyrator filter.

36. A wireless transceiver as recited in claim 35, further comprising an internal limiter coupled with the internal bandpass filter.

37. A wireless transceiver as recited in claim 36, further comprising an internal lowpass filter coupled with the internal limiter.

38. A wireless transceiver as recited in claim 35, wherein a group delay ripple cf the RLC gyrator filter and the bandpass filter is less than 150nS.

39. A wireless transceiver as recited in claim 35, wherein the wireless receiver has an I.F. dynamic range that is greater than 80dB.

40. A wireless transceiver as recited in claim 35, wherein the wireless receiver has an

I.F. dynamic range that is greater than 85dB.

41. A wireless transceiver as recited in claim 40, wherein the RLC gyrator filter generates a negative phase delay ripple, the RLC gyrator filter configured such that the RLC negative phase delay ripple acts as an equalizer for the BPF phase ripple.

42. A wireless transceiver as recited in claim 35, wherein the RLC gyrator filter is overdriven by 15dB.

43. A wireless transceiver as recited in claim 35, wherein the wireless receiver is suitable for FHSS applications utilizing a 2.4GHz Industrial, Scientific, and Medical (ISM) frequency band.

44. A wireless transceiver as recited in claim 35, wherein the wireless receiver is operable on a UHF band.

45. A wireless transceiver as recited in claim 35, wherein the wireless receiver is suitable for use in a cellular phone.

46. A wireless transceiver as recited in claim 35, wherein the wireless receiver is suitable for use in a digital phone.

47. A wireless transceiver as recited in claim 35, wherein the wireless receiver is suitable for use in a wireless radio.

48. A wireless transceiver as recited in claim 35, wherein the transceiver is operable as a WLAN transceiver utilizing a 2.5GHz frequency band.