JP3389164B2 - Frequency conversion circuit - Google Patents

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 in various wireless devices.

[0002]

2. Description of the Related Art Generally, most of the structures of this kind of frequency conversion circuit convert the frequency of an input signal based on the oscillation output of an oscillator. As shown in FIG. 2, the conventional frequency conversion circuit inputs the oscillation output of the local oscillator 6 to the mixer 1 to generate an RF (Radio Freq) signal.
frequency) of the input signal 10. The frequency-converted IF (Intermed)
Iate Frequency) output signal 11 is output from IF amplifier 14.

In this frequency conversion circuit, the 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 by the magnitude of the DC voltage of the received electric field strength RSSI output from the IF amplifier 14 arranged in the subsequent stage. It is generated by the circuit 7. Then, this MIX local level adjustment voltage 1
The attenuation amount of the variable attenuator 12 is controlled by 7 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-described conventional frequency conversion circuit has a structure in which the output of the IF amplifier 14 is fed back to control the attenuation amount of the variable attenuator 12. Therefore, there is a drawback that an unbalanced output waveform is output from the frequency conversion circuit until the local level is adjusted. Further, the circuit configuration is complicated, which is not suitable for downsizing the device. Therefore, it has been expected to realize a frequency conversion circuit that always outputs a balanced output waveform with a simple circuit configuration.

The present invention has been made in order to solve the above-mentioned drawbacks of the prior art, and its object is a frequency conversion capable of balancing the output waveform with a simple circuit configuration and regardless of the input electric field. It is to provide a circuit.

[0006]

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, and an amplification means for amplifying the oscillation output of the oscillator. A bidirectional diode including a pair of diodes connected in opposite directions between the signal line transmitting the input signal and the signal line transmitting the oscillation output to the amplifying means 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.

Further, the amplification means is characterized in that the amplification factor is preset to the maximum gain. Further, it is characterized by further including bias supply means for supplying a bias signal to the amplification means according to the amplified output.

The amplifying means is a transistor element that uses the oscillation output as a base input and increases or decreases the bias signal by a collector output, and the frequency converting means is a mixer that multiplies the amplified output by the input signal. .

In short, this circuit is provided with a circuit for changing the bias voltage of the local amplifying section by the RF input electric field above a certain level in the frequency converting circuit of the receiving section of the mobile communication equipment to which a strong electric field is inputted. is there.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of the present invention will be described with reference to the drawings. In each drawing referred to in the following description, the same parts as those in the other drawings are designated 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 including a transistor element
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 matching the base bias signal so that the maximum gain is obtained, and a matching circuit 5 for oscillating output. And a local oscillator 6 that is input to the.

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. In addition, the IF output terminal of the mixer 1
Obtain the output signal 11.

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 opposite directions and having a predetermined forward voltage.

When an input electric field higher than the forward voltage is input, a current flows through the bidirectional diode 3. Then, the amplification output of the local amplification 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 amplification unit 2 changes. This change reduces the gain of the local amplification unit 2. 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. A bias signal is supplied from the bias supply circuit 4 to the local amplifier 2. Further, a matching circuit 5 is provided which performs matching so as to obtain the maximum gain with this bias signal.

In such a configuration, the RF wave input from the RF input terminal, that is, the RF input signal 10 is input to the mixer 1
At, the frequency is converted by the local wave from the local amplifier 2 and becomes an IF wave, that is, an IF output signal 11.

In this circuit, the 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 (when the electric field is strong), a current flows through the bidirectional diode 3. That is, when the RF input is a strong electric field (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 that receives the amplified output as input 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 having the lowered injection level is also reduced, and the saturation voltage of the mixer 1 is not reached. By working like this,
Even if the strong electric field is input, the 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 the electric field is not strong), no current flows in the bidirectional diode 3. That is, when the RF input is not a strong electric field (the amplitude is small), no current flows in the diode 3 due to the forward voltage characteristic of the diode 3. Therefore, the local amplifier 2 operates in the state of 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 for the IF output signal 11.

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

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

[0024]

As described above, the present invention adopts 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, thereby facilitating integration. There is an effect that.
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, lowering the local level injected into the frequency converter and increasing the gain of the frequency converter. By lowering, 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 drawings]

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

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

[Explanation of symbols]

1 mixer 2 Local amplifier 3 bidirectional diode 4 Bias supply circuit 5 Matching circuit 6 local oscillator

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields investigated (Int.Cl. ⁷ , DB name) H03D 7/00 H04B 1/26

Claims (8)

(57) [Claims] 1. A frequency conversion circuit for converting the frequency of an input signal based on an oscillation output of an oscillator, the amplification means amplifying an oscillation output of the oscillator, a signal line for transmitting the input signal, and the oscillation. A bidirectional diode composed of a pair of diodes having a predetermined forward voltage and connected in opposite directions between a signal line for transmitting an output to the amplifying means, and an amplified output of the amplifying means is used to output the input signal. A frequency conversion circuit comprising a frequency conversion means for converting a frequency. 2. The frequency conversion circuit according to claim 1, wherein the amplification means has an amplification factor set in advance to a maximum gain. 3. The frequency conversion circuit according to claim 1, further comprising bias supply means for supplying a bias signal to the amplification means in accordance with the amplified output. 4. The frequency conversion circuit according to claim 3, wherein the amplification means is a transistor element that uses the oscillation output as a base input and increases or decreases the bias signal by a collector output. 5. The frequency conversion circuit according to claim 4, wherein the frequency conversion means is a mixer for multiplying the amplified output by the input signal. 6. The frequency conversion circuit according to claim 1, wherein the pair of diodes are both Schottky diodes. 7. The bidirectional diode is configured so that a current flows through the pair of diodes when the amplitude value of the input signal becomes larger than the forward voltage. 7. The frequency conversion circuit according to any one of 6 to 6. 8. The frequency conversion circuit according to claim 1, wherein the input signal is an RF signal.