JP2002217774A - Mobile phone - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a mobile phone that can be downsized without deteriorating its disturbing characteristic. SOLUTION: The mobile phone is provided with a low noise amplifier 2 placed at a receiver side high frequency circuit and with a source current supply circuit 6 that controls a source current of the low noise amplifier 2 depending on the communication power.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a portable telephone, and more particularly, to an improvement of a high frequency circuit in a CDMA portable telephone.

[0002]

2. Description of the Related Art Code Division Multiple Acces (CDMA)
The s) system is one of the multiple access systems in which a plurality of mobile stations are connected to one base station, and each mobile station is identified using a unique code. In this method, a signal to be transmitted is dispersed and transmitted over a wide range of spectrum in the entire usable frequency band, which is also called a spread spectrum method. For this reason, the signals of all the stations are superimposed and transmitted in the same frequency band. However, since a unique code is used for each station, identification is possible without interference. CDMA is another known as multiple access
It is said that it is more resistant to interference and disturbance than FDMA and TDMA systems, and has high confidentiality, and can take more channels,
It has been put to practical use in many countries including Japan and North America.

[0003] On the other hand, however, the intermodulation interference ratio is specified in the standard for interference / interference caused by multi-station signals in cells having the same frequency and different frequencies in the same cell. . Especially 8
The 00 MHz cellular band is defined for three-stage input of a desired signal, and in order to satisfy the requirement, an LNA (LNA) provided at the first stage of a high-frequency receiving circuit is mainly used as a method for dealing with interference and interference caused by a mixer circuit. Circuits for controlling the gain of a low-noise amplifier are well known.

[0004] The principle of this method is briefly described as follows. FIG. 4 shows signal input (unit: dBm) on the horizontal axis and signal output on the vertical axis, and shows respective input / output characteristics of the desired signal D and the interference signal U. As can be seen from this figure, the input / output characteristics of the desired signal D and the interference signal U have different slopes. For this reason, the characteristic curves of the two signals have an intersection, which is called an intercept point. IIP3 on the input side is (input 3'rd order intercept point)
Is known as one of the parameters indicating the performance of the nonlinear amplifier. Now, when the input level of the desired signal D to the mixer circuit is a low value of about -90 dBm, the output level is as low as about -75 dBm, and the difference DU from the input level of the interfering signal for generating the same output level. Ratio (Δ1 in the figure)
, The intermodulation performance is satisfied without lowering the gain of the low noise amplifier. On the other hand, when the input level of the desired signal U increases to about -70 dBm, the output level becomes about -55 dBm, and the difference DU ratio (Δ2 in the figure) from the input level of the interfering signal for producing the same output level decreases. By lowering the gain of the low noise amplifier, the regulation of the intermodulation interference ratio is satisfied.

[0005]

By the way, when the miniaturization of the portable telephone is designed with priority as in recent years, the distance between the transmitting circuit and the receiving circuit becomes short inside the portable telephone. In addition, the isolation of the transmission signal from the reception circuit becomes insufficient, and the standard of the single tone interference ratio is not satisfied. One example of a worsening mechanism is that a modulation component of the transmission signal is generated in the interfering signal at the time of single tone measurement (referred to as cross modulation due to the third-order term of the nonlinear element), and a part of this modulation component is a part of the reception IF band. It falls inside and appears as distortion of the desired signal.

An object of the present invention is to provide a portable telephone suitable for miniaturization by compensating for isolation degradation due to miniaturization.

[0007]

In order to achieve the above object,
A mobile phone according to the present invention includes a low-noise amplifier provided in a high-frequency circuit, and a source current supply circuit that controls the magnitude of the source current of the low-noise amplifier according to the magnitude of communication power. .

Here, the source current supply circuit supplies the first source current when the telephone is in a standby state or in a communication state with less power than a predetermined power, and when the telephone is in a communication state with a power equal to or more than the predetermined power, A configuration in which a second source current larger than the first source current is supplied can be employed.
Further, the source current supply circuit is a bias circuit connected to a source terminal of a low noise amplifier, wherein the magnitude of a bias resistor in the source circuit is adjusted to control the magnitude of a bias current.

Further, the source current supply circuit includes a main bias circuit that always supplies a bias current to the source terminal, and a bias current that is in harmony with the main bias circuit when the telephone is in a communication state with power equal to or more than a predetermined power. And a sub-bias circuit for supplying the same.

[0010]

FIG. 1 is a diagram showing a high-frequency circuit of a receiving circuit of a portable telephone according to an embodiment of the present invention. In the figure, reference numeral 1 denotes a duplexer, one terminal of which is connected to an antenna, the other terminal of which is connected to a transmitting circuit, and the other terminal of which is connected to a receiving circuit. Reference numeral 2 denotes a low noise amplifier, and reference numeral 3 denotes a SAW filter as an example of a high frequency filter. A mixer circuit is connected to the output side of the SAW filter.

The duplexer 1 and the low noise amplifier 2
In between, an input matching circuit 4 of the low noise amplifier 2 is provided, and between the low noise amplifier 2 and the SAW filter 3, an output matching circuit / bias supply circuit 5 of the low noise amplifier 2 is provided. The low noise amplifier 2 is, for example,
It is a Ga-As type FET, and its source terminal is provided with a bias circuit 6. The bias circuit 6 includes a main bias circuit 61, a sub bias circuit 62, and a sub bias circuit 62.
And a switch circuit 63 for turning ON / OFF.

The main bias circuit 61 is provided with the Ga-As type FET.
A resistor R that generates a DC bias voltage applied to the source of
1 and bypass capacitors C4 and C5 for bypassing high frequency components flowing from the source terminal. The bias voltage generated by the main bias circuit 61 is represented by V
1. Assume that the bias current is I1. Sub bias circuit 62
Is composed of a resistor R2.

The switch circuit 63 includes two FET switches T
r1 and Tr2. The gates of the FET switches Tr1 and Tr2 receive the IDLE signal and the LNAcontrol signal, respectively. The IDLE signal is a signal indicating whether the mobile phone is in a transmission state or a non-transmission state.
w, the transmission state becomes High. In the CDMA system, standby reception corresponds to a non-transmission state, and communication (transmission and reception) corresponds to a transmission state.

The LNA control signal is high when the transmission output is lower than a predetermined power (when the reception signal level is higher than a reference value) and low when the transmission output is higher than the predetermined power (when the reception signal level is lower than the reference value). Becomes In the CDMA system as in the mobile phone according to the present embodiment, power control is performed to maintain a constant relationship between transmission power and reception power with a radio base station, so whether the transmission output is smaller or larger than a predetermined power is determined. , The received signal level is larger than the reference value. This determination is made by an MSM (Mobil Station MODEM) (not shown) or the like inside the mobile phone.

The relationship between the transmission power and the reception power in the above power control can be simplified to (average transmission power) + (average reception power) = substantially a constant value (for example, -76 dBm). The details of the power control are standardized as open-loop estimation performed by the mobile station and closed-loop correction performed by both the mobile station and the radio base station. In addition, the above constant value is -76.
In the case of dBm, the predetermined power is, for example, 15 dBm.
(In this case, the reference value is -91 dBm). In this case, the LNAcontrol signal has a received signal level of-
High when it is larger than 91 dBm) and Low when it is -91 dBm or less.

According to the states of the IDLE signal and the LNA control signal, the FET switches Tr1 and Tr2 are turned on as shown in the following table.
N / OFF operation.

[0017]

[Table 1]

As can be understood from the above table, the FET switch Tr1 is turned on when the transmission output is higher than a predetermined power,
Otherwise, turn off. And this FET switch Tr
When 1 is turned on, the sub bias circuit 62 is turned on, and the resistor R2 is connected in parallel with the resistor R1 of the main bias circuit 61. Therefore, the bias voltage supplied to the source of the Ga-As type FET,
The bias current is determined by the combined resistance value of the two resistors R1 and R2. The bias voltage at this time is V2, and the bias current is I2.

FIG. 2 shows an example of a characteristic curve of the IIP 3 with respect to the bias current of the low noise amplifier 2, and FIG.
Shows an example of a characteristic curve of the IIP3 with respect to the bias voltage. As understood from these figures, the IIP3 characteristic has little dependence on the bias voltage and has a high dependence on the bias current. In the present embodiment, focusing on the fact that IIP3 has a high dependence on the bias current and a low dependence on the bias voltage, the resistances R1, R
The value of 2 is appropriately determined. That is, the main bias circuit 6
When the bias current is supplied only by the bias circuit 1 and the bias current is indicated by the bias point 1 in FIG. 2, the bias current is supplied by the main and sub bias circuits 61 and 62. Current value I2 indicated by point 2
And As a result, IIP3 in the case of the bias current I1
Is -2.5 dBm, whereas I2 is 6.5
It will increase by about 9.0 dB with dBm.

In FIG. 2, I3 indicates a bias current value (set value in the prior art) that has sufficient circuit space and satisfactory isolation. In the present embodiment, the bias current I1 is smaller than this value, and I2 is larger than that value. Since the bias current I1 is smaller than I3, the power consumption is lower than in the past when the device is on standby or when the transmission power is small. Normally, in mobile phones, the standby time is much longer than the talk time, which can be said to contribute to extending the life of the battery or reducing the size of the battery itself.

In the above embodiment, the resistors R1 and R2 are connected in parallel in FIG. 1, but they may be connected in series. That is, instead of the resistor R2, the resistor R
2 'is connected in series with the resistor R1, and a transistor Tr1 is connected in parallel with the resistor R2' (both ends of the resistor R2 'and T
The drain terminal and the source terminal of r1 may be connected). However, in this case, the series combined resistance of R1 and R2 is the bias current I1, and the resistance R1 is the bias current I1.
A resistance value that gives 2.

Further, in FIG. 1, the bias current is switched in two stages, but it can be switched in three or more stages.

[0023]

As described above, the portable telephone according to the present invention comprises a low-noise amplifier provided in a high-frequency circuit,
Since the configuration includes a source current supply circuit that controls the magnitude of the source current of the low noise amplifier according to the magnitude of the transmission power, the intersection of the desired signal and the interference signal in the IIP3 characteristics of the low noise amplifier is It moves according to the size and can distinguish desired signal and interference signal even when communication power is large, ensuring good anti-jamming characteristics, suitable for further miniaturization to make high-frequency transmission circuit and high-frequency reception circuit closer. There is an effect that.

In addition, the source current of the low-noise amplifier is controlled in accordance with the power consumption, and does not always flow a large source current. It is possible to suppress the increase in power consumption during standby that occupies a long time, and it also contributes to extending the life or miniaturization of the battery, and it is possible to achieve both the improvement of anti-jamming characteristics and the miniaturization. It is a great contribution.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a high-frequency circuit portion of a receiving circuit of a mobile phone according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating IIP3 characteristics with respect to a source current of a low noise amplifier.

FIG. 3 is a diagram illustrating IIP3 characteristics with respect to a source voltage of a low noise amplifier.

Fig. 4 IIP3 in general active devices such as low noise amplifier
It is a figure showing a characteristic.

[Explanation of symbols]

1: Duplexer, 2: Low noise amplifier, 3: SAW
Filter: 4 Input matching circuit, 5: Output matching circuit and bias supply circuit, 6: Bias circuit, 61: Main bias circuit, 62: Sub bias circuit, 63: Switch circuit,

Claims (6)

[Claims] 1. A mobile phone comprising: a low-noise amplifier provided in a high-frequency circuit; and a source current supply circuit that controls the magnitude of a source current of the low-noise amplifier according to the magnitude of transmission power. 2. The source current supply circuit supplies a first source current when the telephone is in a standby state or a transmission state with less power than a predetermined power, and supplies a first source current when the telephone is in a transmission state with power equal to or more than a predetermined power. 2. The mobile phone according to claim 1, wherein a second source current larger than the first source current is supplied. 3. The mobile phone performs power control for maintaining a constant relationship between transmission power and reception power with a radio base station, and the source current supply circuit controls a reception signal level during a call. When the value is larger than the reference value, the first
2. The portable telephone according to claim 1, wherein the second source current is supplied when the received signal level is equal to or lower than the reference value, and the second source current is larger than the first source current. 4. The source current supply circuit is a bias circuit connected to a source terminal of a low noise amplifier,
2. The method according to claim 1, wherein the magnitude of the bias current is controlled by adjusting the value of the bias resistor therein.
The described mobile phone. 5. A source current supply circuit, comprising: a main bias circuit for supplying a bias current to a source terminal; and a bias current which is superimposed on the main bias circuit when the telephone is in a communication state with power equal to or higher than a predetermined power. 5. The mobile phone according to claim 4, further comprising: a sub-bias circuit. 6. The mobile phone according to claim 5, wherein the communication system of the mobile phone is a CDMA system.