JPH0583034A - Frequency conversion circuit - Google Patents

Abstract

PURPOSE:To obtain a frequency conversion circuit with an excellent noise figure whose configuration is suitable for circuit integration by taking large isolation between input and output signals with respect to the frequency conversion circuit suitable for circuit integration. CONSTITUTION:The conversion circuit is provided with a differential pair 101 including transistors (TRs), load resistors 102, 103, bias resistors 104, 105, and a current source 106, with a distribution circuit 112 which applies a high frequency signal and a local oscillation signal to each input terminal of the differential pair 101 and extracts an inverting high frequency signal and an inverting local oscillation signal at each output terminal, with a TR 107, a load resistor 108 and a current source 109, and with two single end mixer circuits 110, 111 receiving an output of the distribution circuit 112 at its input terminal and synthesizing the outputs at its output terminal as an intermediate frequency signal.

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 suitable for an integrated circuit (IC) used in a mobile phone or the like. High-frequency mobile circuits used in mobile phones and the like are required to be ultra-miniaturized, and circuits that are conventionally composed of individual parts are also required to be integrated. The present invention has been made in view of such circumstances.

[0002]

2. Description of the Related Art As shown in FIG. 4, a conventional frequency conversion circuit using a transistor applies an oscillating voltage having two different frequencies, for example, a high frequency signal RF and a local oscillating signal Lo to a non-linear circuit simultaneously to obtain a Lo signal. It utilizes the fact that the input conductance changes periodically according to the voltage and the signals of the sum and difference of both frequencies are output. Also,
Gilbert announced in 1968 by Gilbert
A multiplication circuit called a cell is also integrated into an IC and used for frequency conversion. (Nikkei Electronics, 1989,
See 7.10 (No. 477))

[0003]

However, the circuit of FIG. 4 has a drawback in that isolation between ports is not achieved. Therefore, measures such as a filter for removing the RF signal and the Lo signal are required for the tuning circuit for the RF signal and the Lo signal and the IF (intermediate frequency) output port. These are difficult to be integrated into an IC, and the circuit of FIG. 4 is unsuitable to be integrated into an IC. Also, although Gilibert cell is suitable for IC, it has a problem in noise figure (NF).
Therefore, it is an object of the present invention to obtain a frequency conversion circuit which has isolation between input and output signals, is composed of a transistor, a resistor and a capacitor, is suitable for an IC, and has an excellent noise figure.

[0004]

In the present invention, as shown in FIG.
And a differential pair 10 including a transistor pair, as illustrated in FIG.
1, load resistors 102 and 103 for the differential pair, bias resistors 104 and 105 for the differential pair, and a current source 106 for the differential pair, and are provided at respective input terminals of the differential pair 101. A distribution circuit 1 which applies a high frequency (RF) signal and a local oscillation (Lo) signal, and extracts a high frequency signal and a local oscillation signal of the opposite phase at respective output terminals.
12 and one transistor 107, respectively
Two load resistors 108 of the transistor and a current source 109 of the transistor 107 are provided, each input terminal receives the output of the distribution circuit 112, and the output terminals combine the two to generate an intermediate frequency (IF) signal. A frequency conversion circuit including single-ended mixer circuits 110 and 111 is provided.

[0005]

When the above circuit is used, the frequency conversion circuit can be composed of only a transistor, a resistor, and a capacitor, which facilitates the formation of an IC. Further, the two input signals are canceled out and not output as an output signal, and the isolation between the input signals is secured by the isolation between the collector and the base of the transistor. The noise figure is also improved over conventional circuits.

[0006]

1 is a circuit diagram of a frequency conversion circuit as a first embodiment of the present invention. This circuit includes a differential pair 101 including two transistors, and a resistor 10 connected to the collectors of the transistors as a load for the differential pair 101.
2, 103, bias resistors 104, 105 connected to the bases of the transistors, and a distribution circuit 112 comprising current sources 106 connected to the emitters of the transistors.
And a single-ended mixer circuit 110 including one transistor 107, a resistor 108 as a load of the transistor 107, and a current source 109 connected to the emitter of the transistor 107, and another single-ended mixer circuit 110 having exactly the same configuration. It is composed of 111. The current source of the single-ended mixer circuit is bypassed by the capacitor.

A high frequency (RF) signal and a local oscillation (local oscillation: Lo) signal are applied to the input ends of the differential pair 101, and one output of the differential pair is supplied to the load resistor 102 and the single end mixer circuit 110. The other output of the differential pair 101 is applied to the load resistor 103 and the input end of the single-ended mixer circuit 111. Furthermore, the outputs of the single-ended mixer circuits 110 and 111 are combined at the output end,
Supply to the intermediate frequency (IF) signal output. In the figure, V _CC indicates a power supply voltage, and V _B1 to V _B4 indicate bias voltages.

The local oscillator signals input to the differential pair 101 are distributed in opposite phases at the two output terminals, and the two distributed local oscillator signals are respectively fed to the single-end mixer circuit 110,
Give to 111. Similarly, the RF signals input to the differential pair 101 are also in anti-phase with the single-ended mixer circuits 110 and 111.
Entered in. Single-end mixer circuits 110, 11
At the output terminal of No. 1, the RF signal and the local oscillation signal have opposite phases to each other, and thus are canceled. This reduces noise. Since the IF signal obtained by multiplying both signals by the single end mixer circuits 110 and 111 is output in the same phase,
After being combined, the IF signal is taken out from the IF signal output terminal. The isolation between the RF signal input end and the local signal input end is determined by the isolation between the collector and base of the transistor.

FIG. 2 shows a second embodiment of the present invention.
In this circuit, the collectors of the transistors of the two single-end mixer circuits of FIG. 1 are common, the emitters are common (201, 202), and the load resistance and the current source are shared to form the resistance 203 and the current source 204. Is. Other than this, the circuit is similar to that of FIG.

FIG. 3 shows a modification of the second embodiment of the present invention. This circuit is obtained by adding a buffer amplifier 310 to the circuit of the second embodiment. That is, the differential pair 30
1, load resistors 302 and 303, bias resistors 304 and 3
05, a distribution circuit including a current source 306, a single-end mixer circuit including a transistor pair 309, a load resistor 307, and a current source 308, three transistors, two resistors, and two capacitors Buffer amplifier 310. Buffer amplifier 3
Reference numeral 10 is a known circuit, which is suitable for an IC circuit because a gain can be obtained with a smaller current value as compared with a normal emitter follower circuit.

[0011]

According to the present invention, it is possible to obtain a frequency conversion circuit which has a large isolation between input and output signals, is composed of a transistor, a resistor and a capacitor, is suitable for an IC, and has an excellent noise figure.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a frequency conversion circuit according to a first embodiment of the present invention.

FIG. 2 is a circuit diagram of a frequency conversion circuit according to a second embodiment.

FIG. 3 is a circuit diagram of a modification of the frequency conversion circuit of the second embodiment.

FIG. 4 is a circuit diagram of a conventional frequency conversion circuit.

[Explanation of symbols]

101 ... Differential pair 102,103 ... Load resistance 104,105 ... Bias resistance 106 ... Current source 107 ... Transistor 108 ... Load resistance 109 ... Current source 110,111 ... Single end mixer circuit 112 ... Distribution circuit 201,202 ... Transistor 203 ... load resistance 204 ... current source 301 ... differential pair 302, 303 ... load resistance 304, 305 ... bias resistance 306 ... current source 307 ... load resistance 308 ... current source 309 ... transistor pair 310 ... buffer amplifier V _B1 , V _B2 , V _B3 , V _B4 ... Bias voltage V _CC ... Power supply voltage

Claims (2)

[Claims] 1. A differential pair (101) including a transistor pair.
And a load resistance (102, 103) for the differential pair,
Bias resistors (104, 105) for the differential pair,
A current source (106) for the differential pair is provided, and a high frequency (RF) signal and a local oscillation (Lo) signal are applied to each input terminal of the differential pair (101), and a reverse phase is applied at each output terminal. Distribution circuit (112) for extracting the high frequency signal and the local oscillation signal of the opposite phase, one transistor (107) and the load resistance (10) of the transistor, respectively.
8) and the current source (10) of the transistor (107).
9), and the distribution circuit (11
The output of 2) is received and combined at the output end to obtain the intermediate frequency (I
F) Two single-ended mixer circuits (11
0, 111). 2. The frequency conversion circuit according to claim 1, wherein the collectors of the respective transistors of the two single-ended mixer circuits are made common, the emitters thereof are made common, and the load resistance and the current source are shared.