JP2001077632A - Frequency conversion circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To balance an output waveform in spite of an input electric field, using simple circuit constitution. SOLUTION: A bidirectional diode 3 is installed between an RF(radio frequency) input terminal and the base of a local amplifier 2. When the amplitude of an RF input signal 10 is large (when electric field is strong), current flows in the bidirectional diode 3, and a base voltage applied to the local amplifier 2 is changed. Base bias current from a bias supply circuit 4, where the amplification output is set to be input, changes. A matching condition with a matching circuit 5 collapses with the change in bias current, the gain of the local amplifier 2 is reduced and output power is decreased. The frequency conversion gain of a mixer 1 receiving a local wave, whose injection level drops in reduced, and voltage does not reach the saturation voltage of the mixer 1. Although a strong electric field is inputted, the IF(intermediate frequency) output signal 11 of a balanced output waveform can be obtained from the IF output terminal of the mixer 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency conversion circuit, and more particularly to a frequency conversion circuit used for various wireless devices.

[0002]

2. Description of the Related Art In general, many types of frequency conversion circuits convert the frequency of an input signal based on the oscillation output of an oscillator. As shown in FIG. 2, a conventional frequency conversion circuit inputs an oscillation output of a local oscillator 6 to a mixer 1 to generate an RF (Radio Freq) signal.
uency) is a configuration for performing frequency conversion of the input signal 10. The frequency-converted IF (Intermed
iate Frequency) output signal 11 is output from the IF amplifier 14.

In this frequency conversion circuit, a mixer 1
The MIX local level adjustment voltage 17 which is determined in advance so as to obtain a balanced output waveform from the output of the mixer 1 is adjusted according to the magnitude of the DC voltage of the received electric field strength RSSI output from the IF amplifier 14 arranged at the subsequent stage. Generated by the circuit 7. The MIX local level adjustment voltage 1
7 controls the amount of attenuation of the variable attenuator 12 to adjust the MIX local level. By controlling the gain of the frequency conversion circuit in this way, a balanced output waveform is obtained.

[0004]

The above-mentioned conventional frequency conversion circuit has a configuration in which the output of the IF amplifier 14 is fed back to control the attenuation of the variable attenuator 12. Therefore, there is a disadvantage that an unbalanced output waveform is output from the frequency conversion circuit until the local level is adjusted. In addition, there is also a disadvantage that the circuit configuration is complicated, and thus it is not suitable for miniaturization of the device. Therefore, realization of a frequency conversion circuit that always outputs a balanced output waveform with a simple circuit configuration has been expected.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned drawbacks of the prior art, and has as its object to provide a simple circuit configuration and a frequency converter capable of balancing output waveforms regardless of an input electric field. Is to provide a circuit.

[0006]

SUMMARY OF THE INVENTION A frequency conversion circuit according to the present invention is a frequency conversion circuit for converting the frequency of an input signal based on the oscillation output of an oscillator, wherein the amplification means amplifies the oscillation output of the oscillator. A bidirectional diode comprising a pair of diodes connected in a reverse direction to each other between a signal line transmitting the input signal and a signal line transmitting the oscillation output to the amplifying unit, and having a predetermined forward voltage; Frequency conversion means for converting the frequency of the input signal using the amplified output of the amplification means.

The amplification means is characterized in that the amplification factor is set to a maximum gain in advance. Further, the apparatus further includes a bias supply unit that supplies a bias signal to the amplification unit according to the amplification output.

The amplifying means is a transistor element having the oscillation output as a base input and increasing or decreasing the bias signal by a collector output, and the frequency converting means is a mixer for multiplying the amplified output by the input signal. .

In short, the present circuit is provided with a circuit for changing the bias voltage of the local amplifying unit with an RF input electric field of a certain level or more in a frequency conversion circuit of a receiving unit of a mobile communication device to which a strong electric field is input. is there.

[0010]

Next, an embodiment of the present invention will be described with reference to the drawings. In the drawings referred to in the following description, the same parts as those in the other drawings are denoted by the same reference numerals.

FIG. 1 is a block diagram showing an embodiment of a frequency conversion circuit according to the present invention. In the figure, a mixer 1 and a local amplifier 2 composed of a transistor element are shown.
, A bidirectional diode 3, a bias supply circuit 4 for supplying a base bias signal to the local amplifier 2, a matching circuit 5 for performing matching with the base bias signal so as to have a maximum gain, and a matching circuit 5 for oscillating output. And a local oscillator 6 that is input to

The output terminal of the matching circuit 5 is connected to the bias supply circuit 4, the diode 3, and the base terminal of the local amplifier 2. The collector terminal of the local amplifier 2 is connected to the bias supply circuit 4 and the mixer 1.

The RF input terminal of the mixer 1 receives the RF input signal 10 and is also connected to the bidirectional diode 3. Also, the IF output terminal of the mixer 1
An output signal 11 is obtained.

The bidirectional diode 3 is provided between the RF input terminal and the base of the local amplifier 2, that is, between the signal line transmitting the RF input signal 10 and the signal line transmitting the oscillation output to the amplifier 2. ing. The bidirectional diode 3 is composed of a pair of diodes connected in the opposite directions and having a predetermined forward voltage.

When an input electric field equal to or more than the forward voltage is input, a current flows through the bidirectional diode 3. Then, the amplified output of the local amplifying unit 2, which is set to the maximum gain in advance, also changes. As a result, the base bias voltage supplied from the bias supply circuit 4 to the local amplifier 2 changes. Due to this change, the gain of the local amplification unit 2 decreases. As a result, the gain of the frequency conversion circuit also decreases, and the output voltage of the frequency conversion circuit does not reach the saturation voltage. Therefore, a balanced output waveform can be obtained for the IF output signal 11.

In such a configuration, the local wave oscillated by the local oscillator 6 is amplified by the local amplifier 2 and injected into the mixer 1. The local amplifier 2 is supplied with a bias signal from a bias supply circuit 4. Further, a matching circuit 5 is provided for performing matching so that the bias signal has the maximum gain.

In this configuration, the RF wave input from the RF input terminal, that is, the RF input signal 10 is
Is converted by the local wave from the local amplifier 2 into an IF wave, that is, an IF output signal 11.

In this circuit, a bidirectional diode 3 is provided between the RF input terminal and the base of the local amplifier 2. Therefore, when the amplitude of the RF input signal 10 is large (in the case of a strong electric field), a current flows through the bidirectional diode 3. That is, when the RF input is a strong electric field (having a large amplitude), a current flows through the diode 3 due to the forward voltage characteristic of the diode 3.

Then, the base voltage applied to the local amplifier 2 changes, and the base bias current from the bias supply circuit 4 which receives the amplified output changes. Due to this change in the bias current, the matching condition with the matching circuit 5 is broken, the gain of the local amplifier 2 is reduced, and the output power is reduced.

The frequency conversion gain of the mixer 1 that has received the local wave whose injection level has decreased also decreases, and the saturation voltage of the mixer 1 does not reach. By working this way,
Even if a strong electric field is input, an IF output signal 11 having a balanced output waveform can be obtained from the IF output terminal of the mixer 1.

On the other hand, when the amplitude of the RF input signal is small (when there is no strong electric field), no current flows through the bidirectional diode 3. That is, when the RF input is not a strong electric field (small amplitude), no current flows through the diode 3 due to the forward voltage characteristic of the diode 3. Therefore, the local amplifier 2 operates in the state of the maximum gain, and its output is injected into the mixer 1. However, since the amplitude of the RF input signal is small, the saturation voltage of the mixer 1 is not reached. Therefore, even in this case, a balanced output waveform is obtained as the IF output signal 11.

As described above, by adopting a simple circuit configuration in which a bidirectional diode pair is provided between the input of the frequency conversion circuit and the base of the local amplifier, integration is easy, and The mobile radio communication terminal can be made smaller.

By changing the type of the diode pair constituting the bidirectional diode 3 and changing the forward voltage characteristics, the output waveform of the IF output signal 11 can be made more balanced. For example, a well-known Schottky diode having a low forward voltage (about 0.3 V) may be used. Thus, if the bidirectional diode 3 is formed by a diode pair having a smaller forward voltage, a current flows through the diode 3 even when the amplitude of the RF input signal is smaller, and the matching condition is broken. As a result, the gain of the local amplifier 2 is reduced, and the frequency conversion gain of the mixer 1 is reduced.
The IF output signal 11 having a balanced output waveform can be obtained.

[0024]

As described above, the present invention can be easily integrated by adopting a simple circuit configuration in which a bidirectional diode pair is provided between the input of the frequency conversion circuit and the base of the local amplifier. There is an effect that is.
In addition, when a strong electric field is input to the frequency conversion circuit, a current flows through the diode pair, and changes the base voltage of the local amplifier, thereby lowering the local level injected into the frequency converter and increasing the gain of the frequency converter. , The saturation voltage of the frequency converter is not reached, so that the output waveform of the frequency conversion circuit is balanced regardless of the input electric field.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a frequency conversion circuit according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a configuration of a conventional frequency conversion circuit.

[Explanation of symbols]

 Reference Signs List 1 mixer 2 local amplifier 3 bidirectional diode 4 bias supply circuit 5 matching circuit 6 local oscillator

Claims (8)

[Claims] 1. A frequency conversion circuit for converting the frequency of an input signal based on the oscillation output of an oscillator, comprising: amplifying means for amplifying the oscillation output of the oscillator; a signal line transmitting the input signal; A bidirectional diode consisting of a pair of diodes connected in a reverse direction to each other between a signal line transmitting an output to the amplifying means and having a predetermined forward voltage, and an amplified output of the amplifying means, Frequency conversion means for converting a frequency. 2. The frequency conversion circuit according to claim 1, wherein said amplification means has an amplification factor set to a maximum gain in advance. 3. The frequency conversion circuit according to claim 1, further comprising a bias supply unit that supplies a bias signal to the amplification unit according to the amplified output. 4. The frequency conversion circuit according to claim 3, wherein said amplifying means is a transistor element having said oscillation output as a base input and increasing or decreasing said bias signal by a collector output. 5. The frequency conversion circuit according to claim 4, wherein the frequency conversion means is a mixer that multiplies the amplified output by the input signal. 6. The frequency conversion circuit according to claim 1, wherein said pair of diodes are both Schottky diodes. 7. The bidirectional diode according to claim 1, wherein a current flows through the pair of diodes when an amplitude value of the input signal is larger than the forward voltage. 7. The frequency conversion circuit according to any one of claims 6 to 6. 8. The frequency conversion circuit according to claim 1, wherein said input signal is an RF signal.