WO2007060464A1

WO2007060464A1 - Circuit for dect device

Info

Publication number: WO2007060464A1
Application number: PCT/GB2006/004425
Authority: WO
Inventors: Minoru Yamada; Malcolm Stephen Jacobs-Paton
Original assignee: Suncorp Technologies Limited
Priority date: 2005-11-25
Filing date: 2006-11-27
Publication date: 2007-05-31
Also published as: GB0524098D0

Abstract

A circuit (20) for receiving and processing RF DECT signals. The circuit comprises an antenna input connectable to an antenna (2) for receiving RF signals, a first amplifier (8) connected for amplifying the received RF signals, a receiver filter (3b) connected for filtering the RF signals amplified by the first amplifier (8) and a receiver input connectable to a second amplifier (7) for further amplifying the filtered RF signals. The first amplifier (8) is a low noise amplifier. The circuit may additionally have the ability to transmit RF DECT signals. In this case, the circuit may further comprise a transmitter amplifier (5) connected for amplifying RF signals to be transmitted, a transmitter filter (3a) connected for filtering the RF signals amplified by the transmitter amplifier, and an antenna switch (4) connected to the antenna input for switching between a transmitting mode for transmitting RF DECT signals and a receiving mode for receiving RF DECT signals.

Description

CIRCUIT FOR DECT DEVICE

[001] The present invention relates to a circuit for receiving and processing RF DECT signals, which can be used in a cordless telephone and base station, enabling wireless communication therebetween.

[002] Communications devices which use the DECT (Digital Enhanced Cordless Telecommunications) standard are commonly used in both domestic and corporate environments . [003] DECT telephones for domestic use typically comprise a fixed base station which is connected to the PSTN (Public Service Telephone Network) , and one or more portable handsets in wireless communication with the base station. [004] For corporate use, typically, a number of fixed base stations are connected to a company' s internal switchboard. Personnel carry portable handsets which are able to communicate via a wireless connection with any one of the base stations that is within range, in order that calls may be put through to them from the switchboard, irrespective of their location.

[005] However, DECT is a cellular system, and the cell radius, i.e., the range within which a handset may be in communication with a base station (the communication range) , is determined by a number of factors. [006] These factors include the strength of the RF (radio frequency) signals transmitted between handset and base station (the RF transmission power) , antenna design, RF bandwidth and frequency, modulation depth, receiver sensitivity, the physical location of the handset and the base unit and ambient conditions.

[007] However, the maximum radiated RF power, the RF bandwidth and frequency, the modulation depth and the maximum bit and frame error ratio (the receiver sensitivity) are all defined in ETSI EN 300 175-2, the current ETSI (European Telecommunications Standards Institute) standard for DECT devices. Thus, varying these factors to increase the communication range is not possible within the ETSI standard. [008] Significant among the factors which affect the communication range is the RF transmission power. Not only is the maximum radiated RF power defined in the ETSI standard, but increasing the RF transmission power is undesirable, because of the potential for interference with other devices, and potential detrimental effects on human health. Accordingly, increasing the transmission power to increase the communication range is not an option.

[009] For this reason, known DECT devices typically have a range in the region of only 25 to 100 metres. The maximum range, achievable in ideal conditions within the ETSI standard, is only about 300 to 400 metres. [0010] Thus, in large domestic properties, it may not be possible for a handset to be reliably in communication with the base station throughout the property. This means that the occupier of the property will only be able to use their hand set in certain limited areas. Alternatively, they can invest in a corporate system with multiple base stations. However, this significantly increases the cost of their telephone system.

[0011] Further, with the limited communication range of current DECT systems, large office premises require many base stations in order to ensure that all areas are covered, thereby making DECT telephone systems expensive for large office premises.

[0012] It is an object of the present invention to overcome the problems associated with the prior art by extending the communication range for DECT devices, without increasing the RF transmission power.

[0013] According to one aspect of the present invention there is provided a circuit for receiving and processing RF DECT signals, the circuit comprising: - an antenna input connectable to an antenna for receiving RF signals; a first amplifier connected for amplifying the received RF signals, wherein the first amplifier is .a low noise amplifier; a receiver filter connected for filtering the RF signals amplified by the first low noise amplifier; and a receiver input connectable to a second amplifier for further amplifying the filtered RF signals. [0014] With this arrangement, the signal to noise ratio of the RF signals output by the second amplifier can be significantly increased as compared with known DECT front end circuits, resulting in a significant increase in communication range for devices incorporating the circuit. [0015] The circuit may further comprise a second amplifier connected to the receiver input for further amplifying the filtered RF signals and for providing the further amplified RF signals as input to a DECT receiver.

[0016] The circuit may further comprise a DECT receiver connected to the second amplifier for receiving and further processing the signal provided as input thereto by the second amplifier.

[0017] Alternatively, the second amplifier may be incorporated within a DECT receiver for receiving and further processing the signal provided as amplified by the second amplifier.

[0018] Preferably, the DECT receiver may be a transceiver for receiving and transmitting RF signals, the circuit may be for transmitting and processing RF DECT signals, and the antenna may be for transmitting and receiving RF signals. [0019] A transmitter amplifier connected for amplifying RF signals to be transmitted may also be provided. [0020] In preferred embodiments, there is further provided a transmitter filter connected for filtering the RF signals amplified by the transmitter amplifier. [0021] Thus, a single circuit is able to both receive and transmit RF DECT signals.

[0022] Further, the provision of separate transmitter and receiver filters enables the second amplifier to be connected to the receiver filter without affecting the transmitting function of the circuit.

[0023] Preferably, the circuit further comprises an antenna switch connected to the antenna input for switching ^•between a transmitting mode for transmitting RF DECT signals and a receiving mode for receiving RF DECT signals.

[0024] Thus, in the receiving mode, the antenna may be connected by the antenna switch to the second amplifier, the receiver filter and the first amplifier, and for the transmission mode, the antenna may be connected via the antenna switch to the transmitter filter and the third amplifier.* . i

[0025] Preferably, the first low noise amplifier is connected to the antenna switch to minimize connection losses therebetween. [0026] In this way, the signal to noise ratio of the RF signals output by the first amplifier can be increased still further.

[0027] The circuit preferably operates to receive and transmit RF signals at 1.9GHz. [0028] According to another aspect of the present invention there is provided a cordless telephone comprising a circuit as described above.

[0029] According to yet another aspect of the present invention there is provided a base* station for a cordless telephone comprising a circuit as described above.

[0030] According to yet another aspect of the present invention there is provided a cordless telephone and base station, each comprising a circuit as described above. [0031] The present invention is described below with reference to the accompanying drawings in which:- [0032] Figure 1 is a circuit diagram of a known front end circuit for a DECT device; and

[0033] Figure 2 is a circuit diagram embodying the present invention. [0034] A conventional front end circuit 10 for a DECT device is shown in figure 1. The circuit comprises a DECT transceiver 1 for providing DECT RF signals for transmission, and for demodulating received DECT RF signals. [0035] The circuit further comprises an antenna 2 for transmitting and receiving 1.9GHz RF signals. The antenna 2 is connected to a band pass filter (RF filter) 3, which filters both transmitted and received RF signals for the DECT frequency, to reduce the transmission harmonics and reduce the unwanted frequency for the receiver. The RF filter 3 is connected to an antenna switch 4 which switches the RF signal pass between transmitting mode and receiving mode. For transmitting mode, the antenna switch 4 is connected to the DECT transceiver I₁ via a power amplifier 5. For receiving mode, the antenna switch is connected to the DECT transceiver 1, via a 90 degrees phase shifter 6 and a low noise amplifier (LNA) 7.

[0036] In the circuit of figure 1, the ratio of the RF carrier signal level received at the DECT transceiver to the noise level due to the front end circuitry is given by formula (1), in which C_lnao is the RF carrier signal level and ^Ni_nao is the noise level. Thus, C_lnao/N_lnao is the RF carrier signal level to noise level ratio at the output of the low noise amplifier 7 in dB. The derivation of formula (1) is given in Annex A.

C_lnao/N_lnao [ dB] = C_ant - F_loss - ASW_loss - A_loss - B_loss - NF

- 201og { ( RkTB ) ¹⁴ . 10⁶} ( 1 )

[0037] In formula 1:- C_ant is the antenna input RF signal level in dBμV; ^Fi_oss is the filter loss, i.e., the loss at the RF filter

3 in dB;

^ASW_loss is the loss at the antenna switch 4 in dB;

^i_oss is the connection loss between the RF filter 3 and the antenna 2 in dB;

Bi_oss is the connection loss between the RF filter 3 and the low noise amplifier 7 in dB, including the loss due to the 90 degree phase shifter 6;

NF is the noise figure of the low noise amplifier 7 in dB (see Annex C) ;

R is the impedance of the low noise amplifier 7 in ohms (Ω) ; k is the Boltzmann constant (= 1.38xlO^~23 J/K);

T is the absolute temperature in Kelvin (K); and

B is the bandwidth in Hertz (Hz) .

[0038] Typical values for the above quantities are indicated in Table 1.

TABLE 1

[0039] According to the values indicated in Table 1, the signal level to noise ratio at the output of the LNA 7 computed using formula (1) is 12.8 dB.

[0040] With currently acceptable RF transmission powers, this results in a maximum communication range in ideal conditions of about 300 to 400 metres with current DECT models.

[0041] With the present invention, an alternative front end circuit architecture is provided, which results in a significant increase in the RF carrier signal to noise ratio being achieved, with a consequent increase in the communication range, without increasing the RF transmission power. In particular, ranges of the order of 1 km have been shown to be possible with the present invention. [0042] An embodiment of the present invention is described below with reference to figure 2. [0043] Figure 2 shows a front end circuit 20 for a DECT device which embodies the present invention. Those components common to figures 1 and 2 bear the same reference numbers in both figures. [0044] As with the known front end circuit architecture 10, the circuit comprises a DECT transceiver 1 for providing DECT RF signals for transmission, and demodulating received DECT RF signals. Further, an antenna 2 for transmitting and receiving 1.9GHz RF signals is connected to an antenna switch 4 which switches the RF signal pass between transmission mode and receiving mode. For transmission mode, the antenna switch 4 is connected to the DECT transceiver 1, via a power amplifier 5. For receiving mode, the antenna switch is connected to the DECT transceiver 1, via a 90 degrees phase shifter 6 and a low noise amplifier (LNA) 7.

[0045] However, with the present invention, there is no RF filter between the antenna 2 and the antenna switch 4. Rather, a separate RF filter is provided for each of the transmitting and receiving modes. In this respect, an RF filter 3a is connected between the antenna switch 4 and the power amplifier 5 for the transmitting mode, and an RF filter 3b is connected immediately before the 90 degrees phase shifter 6 for the LNA 7 for the receiving mode. [0046] Additionally, a further low noise amplifier (Pre- LNA) 8 is provided between the antenna switch 4 and the RF filter for received signals 3b. The further low noise amplifier 8 is connected to the antenna switch 4 to minimize the connection loss therebetween. [0047] Using appropriate semiconductor technologies, the further low noise amplifier 8 can be selected to be a very low noise type, and to have a high gain. In the present embodiment, the further low noise amplifier 8 is a gallium arsenide field-effect transistor (GaAs-FET) . [0048] In the circuit of figure 2, the ratio of the RF carrier signal level received at the DECT transceiver 1, to the noise level due to the front end circuitry, is given by formula (2.1) . Again, C_lna0 is the RF carrier signal level and N_lnaotot is the noise level. Thus, C_lnao/N_lnaotot is the RF carrier signal level to noise level ratio at the output of the low noise amplifier 7 in dB.

Cm_ao/N_lnaotot [dB] = C_lnao [dBμV] - N_lnaotot [dBμV] (2.1)

[0049] In formula (2.1) the signal level received at the DECT transceiver 1 C_lnao in dBμV is given by formula (2.2) and the total noise level due to the front end circuitry N_lnaotot in dBμV is given by formula (2.3) .

C_lnao [dBμV] = 201og LNA_G + 201og PRELNA₅ + C_ant - ASW_loss - A_loss - F_loss - B_loss (2.2)

Ni_naotot [dBμV] = 201og{LNA_G . (kTB)¹* . 10⁶ . (F₂ ¹⁴ . R₂ ¹*

+ F₁ ¹⁵ . R₂ ¹⁴ . PRELNA_G . 10 <- ^^ioss - ^BI^OSS)/^2O _{} } (2}.3)

[0050] The derivation of formulas (2.1) to (2.3) is given in Annex B.

[0051] In formulas (2.2) and (2.3):-

C_ant is the antenna input RF signal level in dB;

^Fi_oss is the filter loss, i.e., the loss at the RF filter 3b in dB;

ASW_loss is the loss at the antenna switch 4 in dB;

^Ai_oss is the connection loss between the antenna switch

4 and the antenna 2 in dB;

^Bi_oss is the connection loss between the further low noise amplifier 8 and the low noise amplifier 7 in dB, including the loss due to the 90 degree phase shifter

6;

PRELNAQ is the gain at the further low noise amplifier

8 in dB; LNA₅ is the gain at the low noise amplifier 7 in dB;

R₁ is the impedance of the further low noise amplifier

8 in ohms (Ω) ;

R₂ is the impedance of the low noise amplifier 7 in ohms (Ω) ; k is the Boltzmann constant (= 1.38xlO^"23 J/K) ;

T is the absolute temperature in Kelvin (K); and

B is the bandwidth in Hertz (Hz) .

F₁ is the noise factor of the further low noise amplifier 8 in dB (see Annex C) ; and F₂ is the noise factor of the low noise amplifier 7 in dB (see Annex C) ;

[0052] Typical values for the above quantities are indicated in Table 2.

TABLE 2

[0053] According to the values indicated in Table 2, the RF carrier signal level received at the DECT transceiver 1 computed using formula (2.2) is 39.5 dBμV. The total noise level due to the front end circuitry computed using formula (2.3) is 23.0 dBμV. Therefore, the RF carrier signal level to noise ratio at the output of the LNA 7 computed using formula (2.1) is 16.5 dB, which represents an improvement of 3.7 dB over the known front end circuit of figure 1. The consequent improvement in receiver sensitivity allows a communication range of up to about 1000 metres, i.e. an increase of about 250% over known DECT devices, without increasing the RF transmission power. [0054] As is illustrated by formulas (2.1) to (2.3), the improvement in the RF carrier signal to noise ratio (and thus to the receiver sensitivity) can be attributed in part to the presence of the further low noise amplifier 8 connected between the antenna switch 4 and the RF filter 3a. To facilitate the incorporation of the further low noise amplifier, the RF filter 3b does not act as a transmitting mode filter. Instead, the further RF filter 3a is provided for the transmitting mode. Also contributing to the improvement in the RF carrier signal to noise ratio is the fact that the further low noise amplifier 8 is connected to the antenna^' switch 4 to minimize the connection losses therebetween. Further, the GaAs-FET device used as the further low noise amplifier 8 has low noise and high gain characteristics .

[0055] It will be apparent to a person skilled in the art that further improvement in the RF carrier signal to noise ratio may be achieved with a lower noise and/or higher gain amplifier being employed as the further low noise amplifier 8.

[0056] In particular, it is desirable to employ an amplifier wherein the noise generated inside the amplifier is small compared with the noise input to the amplifier. One method of defining the noise performance of an amplifier is the noise figure (NF) , and the related noise factor F, which is defined as the ratio of the signal to noise power ratio input to the amplifier to the corresponding ratio output from the amplifier. A low noise figure indicates that the noise generated inside the amplifier is small compared with the noise input to the amplifier. Thus, it is desirable to employ an amplifier having a low noise figure as ^'the further low noise amplifier 8. Noise figure is explained in more detail in Annex C. [0057] Ideally the noise figure of the amplifier should be as close to 0 dB as possible. In practice, amplifiers having a noise figure of 0.5 dB, as is the case with the present invention are suitable.

[0058] Although the present invention has been described in relation to the embodiment shown in figure 2, it will be apparent to a person skilled in the art that various modifications of this embodiment are possible.

[0059] In the embodiment of figure 2, the low noise amplifier 7 and the power amplifier 5 for the transmitting mode are both provided as separate components from the DECT transceiver 1. However, it will be readily apparent to the person skilled in the art that either or both of these components may be integrated within the DECT transceiver 1. [0060] It will also be apparent to the person skilled in the art that the requirement for the 90 degree phase shifter 6 depends on the type of amplifier employed as the low noise amplifier 7.

[0061] Further, whilst the embodiment of figure 2 has been described in terms of a circuit which is operable in both transmitting and receiving modes, the advantages of the present invention may equally be employed in a unit which is only operable in receiving mode .

Annex A - Derivation of formula (1)

[0062] The RF carrier signal level input to the low noise amplifier 7 C_lnai in dBμV is given by formula (Al) .

C_lnai [dBμV] = C_ant - F_loss - ASW_loss - A_loss - B_loss (Al )

'[0063] In formula (Al):-

C_ant is the antenna input RF signal level in dBμV; Fi_oss is the filter loss, i.e., the loss at the RF filter 3 in dB;

^ASWi_oss is the loss at the antenna switch 4 in dB; A_loss is the connection loss between the RF filter 3 and the antenna 2 in dB; and

Bi_oss is the connection loss between the RF filter 3 and the low noise amplifier 7 in dB, including the loss due to the 90 degree phase shifter 6.

[0064] Formula (A2) gives the RF signal level input to the low noise amplifier 7 C_lnai in μV.

C_lnai [μV] = 10 ^(Clnai t^{dBμV] )} /²⁰ _(A2 )

[0065] Formula (A3) gives the RF signal level output from the low noise amplifier 7 Ci_nao in μV in terms of the input signal level C_lnai in μV and the gain of the low noise amplifier LNA_G.

Ci_nao [μV] = C_lnai [μV] . LNA_G (A3 )

[0066] The noise factor F of the low noise amplifier 7 is given by formula (A4) .

F = { (Ci_nai [μV] /N₁₁₁₈₁ [μV] ) / (C₁₀₃₀ [μV] /N_lnao [μV] ) }² (A4 )

[0067] In formula (A4):- N_lnai is the noise level input to the low noise amplifier 7 in μV; and

^Ni_nao is the noise level output from the low noise amplifier 7 in μV.

[0068] The gain of the low noise amplifier 7 LNA_G is given by formula (A5) .

LNA_G = C_lnao [μV]/C_lnai [μV] (A5)

[0069] Substituting formula (A5) in formula (A4) and rearranging gives formula (Aβ) .

Ni_nao [μV] = F¹⁴ . LNA_G . N_lnai [ μV] (A6 )

[0070] The noise level input to the low noise amplifier 7 N_lnai in W is given by formula (A7) . N_lnai in W is related to N_lnai in μV by formula (A8) .

N_lnai [W] = kTB (A7)

N_lnai [μV] = (R . N_lnai [W] ) ¹¹ . 10⁶ (A8 )

[0071] In formula (A8),

R is impedance of the low noise amplifier 7 in Ohms

(^Q); k is the Boltzmann constant (= 1.38xlO^"23 J/K) ;

T is the absolute temperature in Kelvin (K) ; and B is the bandwidth in Hertz (Hz) .

[0072] Using formulas (A3) and (A6) , the ratio of the carrier signal level received at the DECT transceiver 1 to the noise level due to the front end circuitry C_lnao/N_lnao is given by formula (A9) .

Cmao/Ninao = (Cinai [μV] . LNA_G) / (F^H . LNA_G . N_lπai [μV]) (A9)

[0073] Thus, Cm_ao/N_lnao [dB] = 201og{C_lnai [μV]/(E* . N_lnai [μV] ) } (AlO)

[0074] Substituting formulas (A2), (Al) and (C2) from Annex C in formula (AlO) gives formula (All) .

Cm_ao/Ni_nao [dB] = C_ant - F_loss - ASW_loss - A_loss - B_loss - NF

- 201og(N_lnai [μV]) (All)

[0075] Substituting formulas (A7) and (A8) in formula

(All) gives formula (A12) , which is formula (1) .

C /N (LNA out) [dB] = C_ant - F_loss - ASW_loss - A_loss - B_loss - NF

- 201OgI(RkTB)¹⁴ . 10⁶} (A12)

Annex B - Derivation of formulas (2.1) to (2.3)

[0076] The RF carrier signal level input to the further low noise amplifier 8 C_prelnai in dBμV is given by formula (Bl) .

C_pr_em_ai C dBμV] = C_ant - ASW_loss - A_loss ( Bl )

[0077] In formula (Bl):-

C_ant is the antenna input RF signal level in dBμV; ASW_l0SS is the loss at the antenna switch 4 in dB; and Ai_oss is the connection loss between the antenna switch 4 and the antenna 2 in dB.

[0078] Formula (B2) gives the RF signal level input to the further low noise amplifier 8 C_prelnai in μV.

C_pr_elnai [ μV] = 10 <^CP^{relnai [dBμV] ) /20} _{( B2} )

[0079] Formula (B3) gives the RF signal level output from the further low noise amplifier 8 C_prelnao in μV in terms of the input signal level C_prelnai in μV and the gain of the further low noise amplifier 8 PRELNA_G.

C_pr_ein_ao [ μV] = C_prelnai [ μV] . PRELNA_G ( B3 )

[0080] The noise factor F₁ of the further low noise amplifier 8 is given by formula (B4) .

F₁ = { ( C_prelnai [μV] /N_prelnai [μV] ) / ( C_prelnao [ μV] /N_prelnao [ μV] ) } ²

(B4) [0081] In formula (B4) :-

N_prei_nai is the noise level input to the further low noise amplifier 8 in μV; and

N_prei_nao is the noise level output from the further low noise amplifier 8 in μV. [0082] The gain of the further low noise amplifier 8 PRELNAg is given by formula (B5) .

PRELNA₆ = C_lnao [μV]/C_lM1 [μV] (B5)

[0083] Substituting formula (B5) in formula (B4) and rearranging gives formula (B6) .

Np_rei_nao [μV] = F₁* . PRELNA₅ . N_prelnax [μV] ( Bβ )

[0084] The noise level input to the further low noise amplifier 8 N_prelnal in W is given by formula (B7) . N_prelnai in W is related to N_prelnai in μV by formula (B8) .

Nprelna, [W] = MB (B7 )

Npreinax [ μV] = ( R₁ . N_prelnai [ W] ) ¹⁴ . 10⁶ ( B8 )

[0085] In formula (B8) ,

R₁ is impedance of the further low noise amplifier 8 in Ohms (Ω) ; k is the Boltzmann constant (= 1.38xlO^"23 J/K) ; T is the absolute temperature in Kelvin (K),"and B is the bandwidth in Hertz (Hz) .

[0086] Using formulas (B3) and (B6) , the ratio of the carrier signal level to the noise level output from the further low noise amplifier 8 C_prelnao/N_prelnao is given by formula (B9) .

C_prelnao/N_prelnao = ( C_prelnai [μV] . PRELNA_G) / ( F₁ ¹⁴. PRELNA₆. N_prelnai [μV] ) ( B9 )

[ 0087 ] Thus ,

C_prei_nao/N_prei_nac [dB] = 2 Olog { C_prelnai [μV] / ( F₁ ¹⁴ . N_prelnai [μV] )

(BlO) [0088] Substituting formulas (B2), (Bl) and (C2) from Annex C into formula (BlO) gives formula (BlI) .

C_preln_ao/N_prelnao [ dB ] = C_ant - ASW_loss - A_loss - NF₁

- 201og(N_prelnai [μV] ) (BlI)

[0089] Substituting formulas (B7) and (B8) into formula (BIl) gives formula (B12) .

C_prelnao/N_prelnao [dB] = C_ant - ASW_loss - A_loss - NF₁ - 201og{ (R . k . T . B)¹* . 10⁶} (B12)

[0090] Formula (B13) and B14 respectively give the signal level and noise levels output from the further low noise amplifier 8 C_prelna0, N_prelnao in dBμV in terms of the corresponding levels in μV.

C_prei_nao [dbμV] = 201og ( C_prelna0 [μV]) (B13)

N_prei_nao [dbμV] = 2 Olog (N_prelnao [μV]) (B14)

[0091] Substituting formulas (B3) and (B6) into formulas (B13) and (B14) respectively gives formulas (B15) and (Blβ) ..

C_prei_nao [dbμV] = 2 Olog ( C_prelnai [μV] . PRELNA₅) (B15)

N_prei_nao [dbμVj = 201Og(F₁" . PRELNA₆ . N_prelnai [μV] ) (Bl^β)

[0092] The RF signal level input to the low noise amplifier 7 C_Xnai in dBμV is given by formula (B17) .

Cm_ai [dBμV] = C_prelnao - F_loss - B_loss (Bl 7)

[0093] In formula (B17) :-

^Fi_oss is the filter loss, i.e., the loss at the RF filter 3b in dB; and Bi_oss is the connection loss between the further low noise amplifier 8 and the low noise amplifier 7 in dB, including the loss due to the 90 degree phase shifter 6; [0094] Formula (B18) gives the RF signal level input to the low noise amplifier 7 C_lnai in μV.

Cma_i [ PV] = 10 ^(Clnai W^Bμ^{V] )} /2⁰ _{( β l 8 )}

[0095] Formula (B19) gives the RF signal level output from the low noise amplifier 7 C_lnao in μV in terms of the input signal level C_lnai in μV and the gain of the low noise amplifier LNA_G.

C_lnao [μV] = C_lnai [μV] . LNA_G ( B19 )

[0096] Formula (B20) is obtained by substituting formulas (B17) and (B18) in formula (B19) .

C_lnao [μV] = LNA_G . 10 ^^pr^eln^ao - Flo^ss - Bl^oss) /2⁰ ( B20 )

[ 0097 ] Thus ,

C_lnao [dBμV] = 20 log LNA_G + C_prelnao - F_loss - B_loss (B21 )

[0098] From formulas (Bl), (B2) and (B3) ,

C_pr_eln_ao [ μV] = 10 ^(Cant - ^ΛSWloss - ^Λloaβ) /²⁰ . PRELNA_G ( B22 )

[0099] Thus,

C_prem_ao [dBμV] = C_ant - ASW_loss - A_loss + 201og PRELNA₅ (B23)

[00100] Formula (B24) , which is formula (2.2), is obtained by substituting formula (B23) into formula (B21) . Ci_nao [dBμV] = 201ogLNA_G + 201ogPRELNA_G + C_ant - ASW_loss - A_loss - F_loss - B₁₀₅₅ (B24 )

[ 00101 ] The noise factor F₂ of the low noise amplifier 7 is given by formula ( B25 ) .

F₂ = { ( C_lnai [μV] /N_lnai [μV] ) / (C_lnao [μV] /N_lnao [μV] ) } ² (B25 )

[00102] In formula (B25):-

^Ni_nai is the noise level input to the low noise amplifier

7 in μV; and

Ni_nao is the noise level output from (generated by) the low noise amplifier 7 in μV. [00103] The gain of the low noise amplifier 7 LNA_G is given by formula (B26) .

LNA_G = C_lnao [μV]/C_lnai [μV] (B26)

[00104] Substituting formula (B26) in formula (B25) and rearranging gives formula (B27) .

Ni_nao [μV] = F₂ ¹⁴ . LNA₅ . N_lnai [μV] (B27 )

[00105] The noise level input to the low noise amplifier 7 N_lnai in W is given by formula (B28) . N_lnai in W is related to N_lnai in μV by formula (B29) .

N₁₀₈₁ [W] = kTB ( B28 )

Nma_x [μV] = (R₂ . N_lnai [W] ) *¹ . 10⁶ (B29 )

[00106] In formula (B29) R₂ is R₂ is the impedance of the low noise amplifier 7 in ohms (Ω) . [00107] The total noise level received at the DECT transceiver 1 N_lnaotot in μV is the sum of the noise generated by the low noise amplifier 7 and the noise from the further low noise amplifier 8, reduced by the loss at the RF filter 3b ^Fi_oss and the connection loss between the further low noise amplifier 8 and the low noise amplifier 7 (including the loss due to the 90 degree phase shifter 6) B_loss, and amplified by the low noise amplifier 7. Thus, using formula (B27),

N_lnaotot [μV] = F₂ ¹* . LNA_G . N_lnai [μV] i LNA_' in (Nprelnao - Floss - Bloss) /20 (B30)

[00108] From formulas (B28) and (B29) ,

N_lnai [μV] = (R₂kTB)^; 10^e (B31)

[00109] From formulas (Bβ.) , (B7) and (B8)

Np_rei_nao [μV] = F₁" . PRELNA_G . (R₁IcTB)*¹ . 10⁶ (B32)

[00110] Thus,

N_prei_nao [dBμV] = 201Og(F₁ ¹⁵ . PRELNAe . (R₁MB)¹⁴ . 10⁶}

(B33) [00111] Formula (B34) is obtained by substituting formulas (B31) and (B33) into formula (B30) .

Nmaotot [μV] = LNA_G . [kTB)^; 10^e (F₂ ¹⁴ . R₂ ¹⁵

+ F₁' R₂ ^*1 . PRELNA_G 2 Q (- Floss - Bloss) /2Oi (B34

[00112] Thus,

Nm_aotot [dBμV] = 201og{LNA_G . (kTB)¹⁵ . 10⁶ . (F₂^ H . R τ>. %

+ F₁ ¹* . R₂^. . PRELNA_G . 10 ^{(~ Floss " Bloss}>/²⁰} } -(B35) [00113] Formula (B35) is formula (2.3).

[00114] The ratio of the carrier signal level received at the DECT transceiver 1 to the noise level due to the front end circuitry C_lnao/N_lnaotot is given by formula (B36) , which if formula (2.1) .

Cinao/Nmaotot [dB] = 201og (C_lnao [μV] /N_lnaotot [μV] )

= 201og (C_lnao [μV] ) - 201og (N_lnaotot [μV] )

= C_lnao [dBμV] - N_lnaotot [dBμV] (B36 )

Annex C - Amplifier Noise Factor (F) and Noise Figure (NF) [00115] The noise factor F for an amplifier is defined as the ratio of the signal to noise power ratio input to the amplifier to the corresponding ratio output from the. That is to say,

F = (S₁ZN₁)Z(S₀ZN₀) (Cl)

[00116] However,, the noise performance of an amplifier is normally specified in terms of its noise figure NF, which is related to the noise factor by formula (C2) .

NF = 10 log F (C2)

[00117] Thus,

NF = 101Og(S₁ZN₁) - lOlog (S₀ZN₀) (C3)

[00118] In formulas (Cl) and (C3):- S₁ is the signal level of the input to the amplifier; N₁ is the noise level of the input to the amplifier; S₀ is the signal level output from the amplifier; and N₀ is the noise level output from the amplifier. [00119] The noise level input to the amplifier is given by formula (C4) .

N₁ = kTB (C4)

[00120] In formula (C4), k is the Boltzmann constant (= 1.38xlO^"23 JZK) ; T is the absolute temperature in Kelvin (K); and B is the bandwidth in Hertz (Hz) .

[00121] According to current standards, the bandwidth B for a DECT device is 1 MHz. The absolute temperature T may be taken to be 25°C (= 25 + 273.15 K = 298.15K). [00122] Using formula (C4), gives a value of 4.11 x 10^"15 W (= -143.86 dBW = -113.86 dBm) for the noise level input to the amplifier, N₁.

[00123] The gain, G of the amplifier is given by formula (C5) .

[00124] The noise generated inside the amplifier N_a is given by formula (C6) .

N_a = N₀ - GN₁ (C6)

[00125] Substituting formulas (C4), (C5) and (C6) into formula (Cl) gives formula (C7) .

F = (N_a+GkBT) /GkBT

(C7)

[00126] Thus,

NF = 101og{ (N_a+GkBT) /GkBT} (C8)

[00127] Thus, for a low noise amplifier in a DECT device having a noise factor NF of about 1.2 dB (F = 1.318), and a gain G of 18, dB (= 63.1), the noise generated inside the amplifier N_a is 8.25 x 10^"14 W (= -130.8 dBW = -100.8 dBm).

[00128] Similarly, for a low noise amplifier in a DECT device having a noise factor NF of about 0.5 dB (F = 1.122), and a gain G of 18 dB (= 63.1), the noise generated inside the amplifier N_a is 3.16 x 10^~14 W (= -135.0 dBW = -105.0 dBm) .

Claims

1. A circuit for receiving and processing RF DECT signals, the circuit comprising :- an antenna input connectable to an antenna for receiving RF signals; a first amplifier connected for amplifying the received RF signals, wherein the first amplifier is a low noise amplifier; a receiver filter connected for filtering the RF signals amplified by the first low noise amplifier; and a receiver input connectable to a second amplifier for further amplifying the filtered RF signals.

2. A circuit as claimed in claim 1 further comprising a second amplifier connected to the receiver input for further amplifying the filtered RF signals and for providing the further amplified RF signals as input to a DECT receiver.

3. A circuit as claimed in claim 2 further comprising a DECT receiver connected to the second amplifier for receiving and further processing the signal provided as input thereto by the second low noise amplifier.

4. A circuit as claimed in claim 2 wherein the second low noise amplifier is incorporated within a DECT receiver for receiving and further processing the signal provided as amplified by the second amplifier.

5. A circuit as claimed in claim 2, 3 or 4 wherein the DECT receiver is a transceiver for receiving and transmitting

RF signals.

6. A circuit as claimed in any preceding claim for transmitting and processing RF DECT signals, wherein the antenna input is connectable to an antenna for transmitting and receiving RF signals .

7. A circuit as claimed in claim 6 further comprising a transmitter amplifier connected for amplifying RF signals to be transmitted.

8. A circuit as claimed in claim 7 further comprising:- a transmitter filter connected for filtering the RF signals amplified by the transmitter amplifier.

9. A circuit as claimed in any one of claims 6 to 8 further comprising an antenna switch connected to the antenna input for switching between a transmitting mode for transmitting RF DECT signals and a receiving mode for receiving RF DECT signals.

10. A circuit as claimed in claim 9 wherein the first low noise amplifier is connected to the antenna switch to minimize connection losses therebetween.

11. A circuit as claimed in any of claims 6 to 10 wherein the circuit operates to receive and transmit RF signals at 1.9GHz .

12. A circuit for receiving, transmitting and processing RF DECT signals, substantially as hereinbefore described with reference to figure 2 of the drawings.

13. A^' cordless telephone comprising a circuit as claimed in any preceding claim.

14. A base station for a cordless telephone comprising a circuit as claimed in any one of claims 1 to 12.

15. A cordless telephone and base station, each comprising a circuit as claimed in any one of claims 1 to 12.