JP3801493B2 - Transceiver using local oscillator - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a local oscillator that generates a local signal having a desired frequency, and a transmission device and a reception device using the local oscillator.
[0002]
[Prior art]
In a conventional transmitter / receiver, the local signal used for transmission / reception signal carrier and frequency conversion processing compares the output of both oscillators with a reference oscillator that oscillates at a fixed frequency, a voltage-controlled oscillator whose oscillation frequency changes according to the control voltage, and so on. Thus, it is generated by a local oscillator having a phase lock circuit for generating the control voltage so that the phases are synchronized with each other (see Japanese Patent Laid-Open No. 8-279775, etc.). That is, in the conventional local oscillator, the output of the voltage controlled oscillator whose oscillation frequency is fixed by the phase fixing circuit is supplied to the transmission / reception circuit unit as it is as a local signal.
[0003]
[Problems to be solved by the invention]
Certainly, in the case of a local oscillator having the above-described configuration, a local signal having a desired frequency can be easily generated by controlling the oscillation frequency of the voltage controlled oscillator by a phase lock circuit.
[0004]
However, in the local oscillator configured as described above, since the oscillation frequency of the voltage controlled oscillator and the frequency of the local signal (that is, the carrier wave frequency of the transmission / reception signal) match, the signal transmitted / received by the antenna is transmitted from the external terminal to the voltage controlled oscillator. It has a problem that it is easy to wrap around and the voltage controlled oscillator tends to cause abnormal oscillation. In particular, in a Bluetooth application device using a 2.4 GHz band high frequency signal, such a trouble due to the wraparound to the voltage controlled oscillator is likely to occur.
[0005]
In view of the above problems, an object of the present invention is to provide a local oscillator capable of generating a stable local signal, and a transmission device and a reception device using the local oscillator.
[0006]
[Means for Solving the Problems]
In order to achieve the above object, a local oscillator according to the present invention includes a reference oscillator that oscillates at a fixed frequency, a control oscillator that changes its oscillation frequency in accordance with a control signal, and compares the outputs of both oscillators to each other. The phase lock circuit for generating the control signal so as to be synchronized with each other, and a multiplier for multiplying the output of the control oscillator to obtain a local signal of a desired frequency.
[0007]
In addition, the transmission apparatus according to the present invention has a configuration using the local oscillator having the above-described configuration as means for generating a local signal serving as a carrier wave of a transmission signal.
[0008]
The receiving apparatus according to the present invention has a configuration using the local oscillator configured as described above as means for generating a local signal used for frequency conversion processing of a received signal.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
In the following description, the local oscillator according to the present invention is applied to a high-frequency signal transmission / reception device (for example, a Bluetooth application device such as a mobile phone, a personal computer, or an AV device). FIG. 1 is a block diagram showing an embodiment of a high-frequency signal transmitting / receiving apparatus according to the present invention.
[0010]
As shown in the figure, the high-frequency signal transmitting / receiving apparatus of this embodiment includes an antenna 1 that transmits and receives digitally modulated high-frequency signals, and a bandpass filter 2 (hereinafter referred to as BPF2) that limits the transmitted / received signals of the antenna 1 to a predetermined frequency band. And the antenna duplexer 3 for sharing the antenna 1 between the transmission and reception systems, the reception circuit unit 4 and the transmission circuit unit 5 connected to the antenna duplexer 3, and the frequencies in both circuit units 4 and 5 And a local oscillator 6 that generates a local signal necessary for the conversion process.
[0011]
The receiving circuit unit 4 mixes the output signal of the LNA 41 and the local signal of the local oscillator 6 with a low noise amplifier 41 (hereinafter referred to as LNA 41) that amplifies the output signal of the antenna duplexer 3, and generates an intermediate frequency signal. An image rejection mixer 42 (hereinafter referred to as IRM 42) for removing an image signal from the intermediate frequency signal, a band pass filter 43 (hereinafter referred to as BPF 43) for limiting the output signal of the IRM 42 to a predetermined frequency band, and a BPF 43. A limiter amplifier 44 (hereinafter referred to as LIA 44), a demodulator 45 that performs demodulation processing on the output signal of the LIA 44, and an internal circuit (not shown) that shapes the output signal of the demodulator 45 And a slicer 46 for feeding to the machine.
[0012]
On the other hand, the transmission circuit unit 5 includes an I / Q quadrature modulator 51 that quadrature modulates a local signal of the local oscillator 6 based on an I signal and a Q signal input from an internal circuit (not shown), and an I / Q quadrature. And a variable gain power amplifier 52 (hereinafter referred to as PA 52) that amplifies the output signal of the modulator 51 and sends the amplified signal to the antenna duplexer 3.
[0013]
Note that the high-frequency signal transmission / reception apparatus of the present embodiment has a configuration in which both the reception circuit unit 4 and the transmission circuit unit 5 are in a differential form. With such a configuration, internal digital noise or the like superimposed on the transmission / reception signal can be canceled in a differential manner, so that the accuracy of the transmission / reception operation can be improved.
[0014]
However, when such a differential format is adopted, the antenna 1 and the BPF 2 are unbalanced circuits, whereas the receiving circuit unit 4 and the transmitting circuit unit 5 are balanced circuits, so that mismatch occurs between them. . Therefore, the antenna duplexer 3 of the present embodiment requires not only a switch function for switching between transmission and reception but also a function as a balun for balancing balance and unbalance.
[0015]
Since the balun described above has to be provided with an inductor having a large inductance value, it has been difficult to integrate it into a semiconductor chip. However, in the high-frequency signal transmitting / receiving apparatus of this embodiment, the receiving circuit unit 4 and the transmitting circuit unit 5 A connection node is formed on a semiconductor chip, a package frame connected to the connection node via a bonding wire, an inductor element by the bonding wire, and a circuit pattern formed between the connection node and the bonding wire A balun is formed using the capacitor element as a component, and the balun is used as the antenna duplexer 3. By adopting such a configuration, it is not necessary to provide a balun as an external part, so that the high-frequency signal transmitting / receiving apparatus can be reduced in size.
[0016]
The high-frequency signal transmitting / receiving apparatus of the present embodiment is configured to cut off the power supply to the transmission circuit unit 5 at the time of reception and stop the operation, and to cut off the power supply to the reception circuit unit 4 at the time of transmission to stop the operation. It is. With such a configuration, the power consumption of the high-frequency signal transmitting / receiving device can be reduced. In addition, when a cascode amplifier is used as the LNA 41, or when an amplifier using an inductor and a diode as a power feeding element is used as the PA 52, impedance matching between the antenna 1, the receiving circuit unit 4, and the transmitting circuit unit 5 becomes easy. .
[0017]
Next, the internal configuration and operation of the local oscillator 6 which is a characteristic part of the high-frequency signal transmitting / receiving apparatus according to the present invention will be described in detail.
[0018]
FIG. 2 is a block diagram showing an embodiment of the local oscillator 6. The local oscillator 6 of the present embodiment includes a reference oscillator 61 (a temperature compensated crystal resonator or the like) that oscillates at a fixed frequency (13 MHz in the present embodiment), and a voltage controlled oscillator 62 whose oscillation frequency changes according to the control voltage. (Hereinafter referred to as VCO [Voltage Controlled Oscillator] 62) and a phase lock circuit 63 (hereinafter referred to as PLL [Phase]) that compares the outputs of both oscillators 61 and 62 and generates the control voltage so that the phases of each of them are synchronized. -Locked-Loop] circuit 63) and a multiplier 64 that multiplies the output of the VCO 62 to obtain a local signal of a desired frequency.
[0019]
The PLL circuit 63 divides the outputs of the reference oscillator 61 and the VCO 62 to generate a frequency-divided signal having a predetermined frequency (500 kHz in this embodiment), and compares the phases of both frequency-divided signals. A phase comparator that obtains an error signal, a charge pump that changes the output level (current value) of the phase comparator, a low-pass filter (current-voltage converter) that converts the output signal of the charge pump into a DC voltage, (Both not shown), and the DC voltage obtained by the low-pass filter is supplied to the VCO 62 as the control voltage. The charge pump is provided for the purpose of high-speed lockup of the PLL circuit 63, and in the present embodiment, the current capability can be changed in the range of 1 mA to 7 mA. When performing spread spectrum communication, the oscillation frequency of the VCO 62 can be changed by controlling the frequency division ratio of the frequency divider.
[0020]
The local signal generated by the local oscillator 6 having the above-described configuration is supplied to the IRM 42 configuring the receiving circuit unit 4 and the I / Q quadrature modulator 51 configuring the transmitting circuit unit 5.
[0021]
The IRM 42 generates a π / 2 phase shifter 420 that generates two signals by shifting the local signal of the local oscillator 6 by 0 and π / 2, an output signal of the LNA 41, and each output signal of the π / 2 phase shifter 420. Multipliers 421 and 422 to be multiplied, band pass filters 423 and 424 (hereinafter referred to as BPF 423 and 424) for limiting the output signals of both multipliers 421 and 422 to predetermined frequency bands, and output signals of both BPFs 423 and 424, respectively. Π / 4 phase shifters 425 and 426 that respectively shift the phase of π / 4, and an adder 427 that adds the output signals of both π / 4 phase shifters 425 and 426.
[0022]
In the case of the IRM 42 configured as described above, the output signal of the LNA 41 and the local signal of the local oscillator 6 are mixed to generate an intermediate frequency signal (2 MHz in the present embodiment) and the image signal can be removed from the intermediate frequency signal. it can. Note that the IRM 42 may be replaced with a double superheterodyne reception signal detection means, but it is desirable to adopt the configuration of this embodiment in view of the circuit scale and cost.
[0023]
The I / Q quadrature modulator 51 includes a π / 2 phase shifter 510 that generates two signals obtained by shifting the local signal of the local oscillator 6 by 0 and π / 2, and a four-phase signal from an internal circuit (not shown). Multiplication of the buffer amplifiers 511, 512, 513, and 514 to which (I, inversion I, Q, and inversion Q) are input and the output signals of the buffer amplifiers 511 and 512 and the output signal of the π / 2 phase shifter 510. 515, a multiplier 516 that multiplies the output signals of the buffer amplifiers 513 and 514 and the other output signal of the π / 2 phase shifter 510, an adder 517 that adds the output signals of both multipliers 515 and 516, and an addition A band-pass filter 518 (hereinafter referred to as BPF 518) for limiting the output signal of the device 517 to a predetermined frequency band.
[0024]
With the I / Q quadrature modulator 51 having the above configuration, the local signal of the local oscillator 6 can be quadrature-modulated based on the I and Q signals input from an internal circuit (not shown). In some cases, the I / Q quadrature modulator 51 may be replaced with direct modulation means using a voltage controlled oscillator. However, in view of various characteristics such as frequency drift, the configuration of this embodiment may be adopted. desirable.
[0025]
Here, the multiplier 64 that constitutes the local oscillator 6 of the present embodiment is configured to multiply the frequency of the input signal by 2 and output the frequency, and the oscillation frequency of the VCO 62 is a frequency that is desired as a local signal in accordance therewith. (In the case of Bluetooth application devices, 2.42 / 2 = 1.21 GHz). That is, it can be said that the local oscillator 6 of this embodiment has a configuration in which the oscillation frequency of the VCO 62 and the frequency of the local signal (that is, the carrier wave frequency of the transmission / reception signal) do not match.
[0026]
With such a configuration, signals transmitted and received by the antenna 1 are less likely to enter the VCO 62 from an external terminal or the like, so that abnormal oscillation of the VCO 62 can be reduced, and a stable local signal can be generated. .
[0027]
The same effect can be obtained by setting the oscillation frequency of the VCO 62 to 1/3, 1/4,..., 1 / n and the multiplier 64 to 3 times, 4 times,. Since the doubler has the simplest configuration for 64, it is desirable to adopt the configuration of this embodiment in view of the circuit scale and cost.
[0028]
【The invention's effect】
As described above, the local oscillator according to the present invention is configured such that the reference oscillator that oscillates at a fixed frequency, the control oscillator that changes the oscillation frequency according to the control signal, and the outputs of both oscillators are synchronized to synchronize their phases. A phase lock circuit for generating the control signal, and a multiplier for multiplying the output of the control oscillator to obtain a local signal of a desired frequency. Further, the transmission device according to the present invention is a configuration using the local oscillator having the above-described configuration as means for generating a local signal that is a carrier wave of the transmission signal, and the reception device according to the present invention is a frequency converter for the received signal. As a means for generating a local signal used for processing, the local oscillator configured as described above is used.
[0029]
This configuration makes it difficult for signals transmitted and received by the antenna to enter the control oscillator from external terminals, etc., so that abnormal oscillation of the control oscillator can be reduced and stable local signals can be generated. It becomes.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an embodiment of a high-frequency signal transmitting / receiving apparatus according to the present invention.
FIG. 2 is a block diagram showing an embodiment of a local oscillator 6;
[Explanation of symbols]
1 Antenna 2 Band pass filter (BPF)
3 antenna duplexer 4 receiving circuit unit 5 transmitting circuit unit 6 local oscillator 41 low noise amplifier (LNA)
42 Image Rejection Mixer (IRM)
43 Band pass filter (BPF)
44 Limiter Amplifier (LIA)
45 Demodulator 46 Slicer 51 I / Q Quadrature Modulator 52 Variable Gain Power Amplifier (PA)
61 Reference oscillator 62 Voltage controlled oscillator (VCO)
63 Phase lock circuit (PLL circuit)
64 Multiplier 420 π / 2 Phase shifter 421, 422 Multiplier 423, 424 Band pass filter (BPF)
425, 426 π / 4 phase shifter 427 Mixer 510 π / 2 phase shifter 511, 512, 513, 514 Buffer amplifier 515, 516 Multiplier 517 Mixer 518 Band pass filter (BPF)

Claims (1)

An antenna that transmits and receives a high-frequency signal, a bandpass filter that limits a transmission / reception signal of the antenna to a predetermined frequency band, an antenna sharer for sharing the antenna with each transmission / reception system, and the antenna sharer A transmission / reception apparatus comprising: a reception circuit unit and a transmission circuit unit; and a local oscillator that generates a local signal necessary for frequency conversion processing in the reception circuit unit and the transmission circuit unit.
The local oscillator generates a control signal such that a reference oscillator that oscillates at a fixed frequency, a control oscillator that changes its oscillation frequency according to a control signal, and outputs of both oscillators are synchronized so that their phases are synchronized. A phase lock circuit; and a multiplier that multiplies the output of the controlled oscillator to obtain a local signal of a desired frequency .
The receiving circuit unit and the transmitting circuit unit are both of a differential type, and the power supply to the receiving circuit unit is cut off during transmission, and the operation is stopped. A transmission / reception device characterized in that the power supply to the unit is cut off and the operation is stopped .

Images