WO2009047736A1

WO2009047736A1 - Wireless transceiver configuration having only one pair of baseband filters

Info

Publication number: WO2009047736A1
Application number: PCT/IB2008/054182
Authority: WO
Inventors: David Duperray
Original assignee: Nxp B.V.
Priority date: 2007-10-12
Filing date: 2008-10-10
Publication date: 2009-04-16

Abstract

A half-duplex wireless transceiver is described that uses one baseband filter pair for both transmitter and receiver operation instead of two. Using only one baseband filter pair reduces the overall die area and therefore the cost of the solution.

Description

WIRELESS TRANSCEIVER CONFIGURATION HAVING ONLY ONE PAIR OF

BASEBAND FILTERS

Currently, many wireless systems use a zero intermediate frequency transceiver architecture. On the transmitter side, this means that the information is directly up-converted at the desired transmit frequency. On the receiver side, this means that the RF modulated signal received at the antenna is directly down converted to DC.

In known wireless transceivers, separate baseband filters are provided for the transmitter and for the receiver. Because the baseband filters on the transmitter and on the receiver chains need large capacitance values, the size of the filters relative to the overall transceiver die area is significant. The filters may occupy, for example, between 20% and 25% of the total die area.

A wireless transceiver is described that uses one baseband filter pair for both transmitter and receiver operation instead of two. Using only one baseband filter pair reduces the overall die area and therefore the cost of the solution. Other features and advantages will be understood upon reading and understanding the detailed description of exemplary embodiments, found herein below, in conjunction with reference to the drawings, a brief description of which is provided below.

FIG. 1 is a block diagram of a wireless transceiver with which the present invention may be used. FIG. 2 is a block diagram of a wireless transceiver that uses one baseband filter instead of two for the transmitter and receiver operation.

FIG. 3 is a block diagram of the wireless transceiver of FIG. 2, illustrating transmit mode. FIG. 4 is a block diagram of the wireless transceiver of FIG. 2, illustrating receive mode. There follows a more detailed description of the present invention. Those skilled in the art will realize that the following detailed description is illustrative only and is not intended to be in any way limiting. Other embodiments of the present invention will readily suggest themselves to such skilled persons having the benefit of this disclosure. Reference will now be made in detail to embodiments of the present invention as illustrated in the accompanying drawings. The same reference indicators will be used throughout the drawings and the following detailed description to refer to the same or like parts. A half duplex wireless transceiver in which the present invention may be used (in this instance a dual band transceiver for 802.1 la/g) is shown in FIG. 1. It works in the 2.4GHz and 5GHz ISM bands. The transceiver architecture consists of three main blocks : the transmitter chains, the receiver chains and the frequency synthesis chain. In the transmitter chains (bottom part of the architecture in FIG. 1), the signal flow is as follows: the information to be transmitted comes from a baseband processor (not shown) as two quadrature signals TXI I and TXI Q. These two signals are passed through baseband transmit re-construction filters 101 1 and 10 I Q which attenuate any aliasing spectrum components coming out of the baseband processor digital-to-analog converters (not shown). After filtering, the signal are up-converted via mixer circuit 102 or mixer circuit 105, and the RF modulated carrier amplitude is amplified via a power amplifier (2G PA if transmitting in the 2.4GHz ISM band or 5G PA if transmitting in the 5GHz ISM band).

In the receiver chains (top part of the architecture in FIG. 1), the signal flow is as follows: an RF modulated signal is present at the input pins of the receiver chain (pins RXI 2G if the receiver is working in the 2.4GHz ISM band or pins RXI 5G if the receiver is working in the

5GHz ISM band). The RF modulated signal is amplified first by a low noise amplifier (2G LNA or 5G LNA), then down-converted by mixer circuit 102' or mixer circuit 105' and filtered by baseband receiver filters 109 1 and 109 Q before being amplified by an AGC circuit 110. The amplified signal is then applied to the baseband processor analog-to-digital converters (not shown) via pins "RXO I" and "RXO Q". The baseband receive filters 109 1 and 109 Q are necessary to knock down any out of band interfering signals.

In an exemplary embodiment, RC calibration circuits 121 and 129 are provided for the transmitter and the receiver filters, respectively.

In the frequency synthesis chain, a VCO 111 is phase locked to a reference frequency by a phase lock loop (PLL) 113. The reference frequency is usually provided by a crystal at pin XTAL. The phase locked VCO signal is divided by a divider 115 and is fed to the mixers of the transmitter and receiver chains.

Because the baseband filters on the transmitter and on the receiver chains need large capacitance values, the size of the filters relative to the overall transceiver die area is significant. In one known 802.1 la/g transceiver, the filters are estimated to occupy between 20% and 25% of the total die area. Referring now to FIG. 2, a block diagram is shown of a wireless transceiver that uses one baseband filter instead of two for the transmitter and receiver operation. As compared to the wireless transceiver of FIG. 1, the transceiver of FIG. 2 has only one baseband filter pair instead of two. It also includes switches for connecting the filter to the receiver and the transmitter chains as needed.

In an exemplary embodiment, a total of twelve switches are provided. They include four double-throw duplexing switches Sl, Sl ', S2 and S2'; four single-throw isolation switches S3, S3', S4 and S4'; and four double-throw band switches S5, S5', S6 and S6'. (Although the switches Sl, Sl ', S2, S2\ S5, S5', S6 and S6' are illustrated and referred to as double-throw switches, they are, strictly speaking, triple-throw switches, the third position of each switch being an open circuit.)

The switch Sl connects a first terminal of the baseband filter 220 1 to a transmit input terminal TXI or to an I output signal of one of the mixer circuits 202' and 205', depending on the state of other switches (namely switch S3 and switch S6). The switch S2 connects a second terminal of the baseband filter 220 1 to the AGC circuit 210 or to an I input signal of one of the mixer circuits 202 and 205, depending on the state of one or more other switches (namely switch S5). Similarly, the switch Sl ' connects a first terminal of the baseband filter 220 Q to a transmit input terminal TXQ or to a Q output signal of one of the mixer circuits 202' and 205', depending on the state of other switches (namely switch S3' and switch S6'). The switch S2' connects a second terminal of the baseband filter 220 Q to the AGC circuit 209 or to a Q input signal of one of the mixer circuits 202 and 205, depending on the state of one or more other switches (namely switch S5').

Switches 3, 3', 4 and 4' are isolation switches. In transmit mode, these switches are open, providing additional isolation between the receiver and the transmitter. In receive mode, these switches are closed to provide I and Q paths from the receiver to the first terminals of the baseband filters 220 1 and 220 Q and from the second terminals of the baseband filters 220 1 and 220 Q to the AGC circuit 209.

The switch S5 connects the second terminal of the baseband filter 220 1 to an I input of the mixer circuit 202 or 205, or the switch may be set to an open state. Similarly, the switch S5' connects the second terminal of the baseband filter 220 Q to a Q input of the mixer circuit 202 or 205, or the switch may be set to an open state. The switch S6 connects the first terminal of the baseband filter 220 1 to an I output of the mixer circuit 202' or 205', or the switch may be set to an open state. Similarly, the switch S6' connects the first terminal of the baseband filter 220 Q to a Q output of the mixer circuit 202' or 205', or the switch may be set to an open state.

When the transceiver is in transmit mode, the switches are configured as shown in FIG. 3 (case shown is when the transmission is done in the 2.4G ISM band). The switches Sl and Sl ' are switched to the transmit input terminals TXI and TXQ, respectively, to the first terminals of the baseband filters 220_I and 220_Q, respectively. The switches S2 and S2' are switched to connect the second terminals of the baseband filters 220 1 and 220 Q, respectively, to the mixer circuit 205 through switches S5 and S5'. The remaining switches are set to an open state to provide isolation.

When the transceiver is in receive mode the switches are configured as shown in FIG. 4 (case shown is when the reception is done in the 2.4G ISM band). The switches S6, S3 and Sl are set to connect an I output of the mixer circuit 202' to the first terminal of the baseband filter 220 1. The switches S2 and S4 are set to connect the second terminal of the baseband filter 220 1 to the AGC circuit 209. Similarly, The switches S6', S3' and Sl ' are set to connect an I output of the mixer circuit 202' to the first terminal of the baseband filter 220 Q. The switches S2' and S4' are set to connect the second terminal of the baseband filter 220 Q to the AGC circuit 209. The remaining switches are set to an open state to provide isolation.

Although embodiments of the present invention have been described in detail, it should be understood that various changes, substitutions and alternations can be made without departing from the spirit and scope of the inventions as defined by the appended claims.

Claims

What is claimed is:

1. A half-duplex wireless transceiver comprising: input terminals including a transmit input terminal; a transmit circuit; a receive circuit; a filter circuit including at least one filter; and a switching circuit coupling the filter circuit to the transmit input terminal, the transmit circuit, and the receive circuit; wherein in a transmit mode, the switching circuit is configured to couple the filter circuit to the transmit input terminal and the transmit circuit to operate as a transmit baseband filter circuit; and in a receive mode, the switching circuit is configured to couple the filter circuit to the receive circuit to operate as a receive baseband filter circuit.

2. The apparatus of Claim 1, wherein the transmit circuit comprises an upconversion circuit and a transmit amplifier.

3. The apparatus of Claim 1, wherein the receive circuit comprises a low-noise amplifier, a downconversion circuit and an AGC circuit.

4. The apparatus of Claim 1, wherein the filter circuit comprises a first terminal and a second terminal, and the switching means comprises a first switch and a second switch.

5. The apparatus of Claim 4, wherein the first switch in a first position couples the first terminal of the filter circuit to transmit input terminal and in a second position couples the first input terminal of the filter circuit to the receive circuit.

6. The apparatus of Claim 5, wherein the second switch in a first position couples the second terminal of the filter circuit to the transmit circuit and in a second position couples the second terminal of the filter circuit to the receive circuit.

7. The apparatus of Claim 6, wherein the switching means comprises a third switch that, in a closed position, couples the first terminal of the filter circuit to the receive circuit if the first switch is in the second position, and that, in an open position, isolates the filter circuit from the receive circuit.

8. The apparatus of Claim 6, wherein the switching means comprises a fourth switch that, in a closed position, couples the second terminal of the filter circuit to the receive circuit if the second switch is in the second position, and that, in an open position, isolates the filter circuit from the receive circuit.

9. The apparatus of Claim 6, wherein the transceiver is an IQ transceiver, the filter circuit comprises an inphase filter and a quadrature phase filter, and the switching circuit comprises further switches corresponding to the first and second switches, respectively, such that in the transmit mode, the switching circuit is configured to couple the both the inphase filter and the quadrature phase filter to the transmit input terminal and the transmit circuit to operate as a transmit baseband filter circuit; and in a receive mode, the switching circuit is configured to couple both the inphase filter and the quadrature phase filter to the receive circuit to operate as a receive baseband filter circuit.

10. The apparatus of Claim 6, wherein the transceiver is a multi-band transceiver.

11. The apparatus of Claim 10, wherein the transceiver operates in a first band of approximately 2GHz and in a second band of approximately 5GHz.

12. The apparatus of Claim 10, wherein the transceiver is a WLAN transceiver.

13. The apparatus of Claim 10, wherein the transmit circuit comprises a first transmit circuit corresponding to a first transmit band and a second transmit circuit corresponding to a second transmit band.

14. The apparatus of Claim 13, wherein the switching means comprises a fifth switch that, in a first position, couples the second terminal of the filter circuit to the first transmit circuit if the second switch is in the first position, and that, in a second position, couples the second terminal of the filter circuit to the second transmit circuit if the second switch is in the first position.

15. The apparatus of Claim 13, wherein the switching means comprises a sixth switch that, in a first position, couples the first terminal of the filter circuit to the first receive circuit if the first switch is in the second position, and that, in a second position, couples the first terminal of the filter circuit to the second receive circuit if the first switch is in the second position.

16. A method of operating a half-duplex transceiver comprising a transmit terminal, a transmit circuit, a receive circuit, a filter circuit and a switching circuit, the method comprising: in a transmit mode, configuring the switching circuit to couple the filter circuit to the transmit input terminal and the transmit circuit to operate as a transmit baseband filter circuit; and in a receive mode, configuring the switching circuit to couple the filter circuit to the receive circuit to operate as a receive baseband filter circuit.

17. The method of Claim 16, wherein the filter circuit comprises a first terminal and a second terminal, comprising, in a transmit mode, isolating the receive circuit from at least one of the first terminal and the second terminal using multiple switches coupled in series.

18. The method of Claim 16, wherein the transceiver is a multi-band transceiver.

19. The method of Claim 16, wherein the transceiver operates in a first band of approximately 2GHz and in a second band of approximately 5GHz.

20. The method of Claim 16, wherein the transceiver is a WLAN transceiver.