JPS5913406A - Frequency converting circuit - Google Patents

Abstract

PURPOSE:To attain stable conversion of frequency by reducing the variation of a local oscillating circuit due to an input signal in case of strong input signal. CONSTITUTION:An intermediate frequency signal having the frequency corresponding to the difference between a local oscillation signal applied to the emitters of transistors (TR) Q1, Q2 and a high frequency signal applied to the base of the TRQ1 is taken out from an output terminal Out through an intermediate frequency transformer T1. An emitter follower TRQ5 is connected to the collector side of a TRQ4 for the local oscillating circuit and a local oscillation signal is applied from the emitter of the TRQ5 to the base of a TRQ3 through a capacitor C1. Even if an input signal is applied to the emitter of the TRQ1 through the capacitor C1, the input signal is attenuated because the emitter impedance of the TRQ5 is low, and signal flow from the emitter to the base is reduced, so that the mixing of the input signal to the local oscillating circuit is extremely reduced.

Description

[Detailed Description of the Invention] When performing frequency conversion, the present invention provides
The purpose is to reduce fluctuations caused by input signals in the local oscillation circuit and to perform stable frequency conversion.

FIG. 1 shows a conventional frequency conversion circuit.

The high frequency signal applied to the input terminal In is transmitted through the transistor Q.
Coil/I/L+, which is added to the emitter of 13 and connected to the collector, is tuned by a variable capacitor VC+. This signal is transmitted by transistor Q, which constitutes the frequency conversion circuit.
1 added to the base. The emitters of transistors Q+, Q2 are coupled to each other, transistors Ql,
The collector of transistor Q5 is connected to the emitter of Q2, and a local oscillation signal is applied to the base of transistor Q3. Therefore, an intermediate frequency signal with a frequency corresponding to the difference between the local oscillation signal applied to the emitters of transistors Qj and Q2 and the high frequency signal applied to the base of transistor Q1 appears from the collector of transistor Q3, and this signal is applied to the collector of transistor Q1. It is taken out from the output terminal Out via the inter-tau frequency transformer T1.

On the other hand, transistor Q4 is a transistor for local oscillation, and has a coil L2 and a variable capacitor VC2 provided at the collector.
It oscillates using a tuned circuit that mainly uses .

Capacitor 02.05 is a feedback capacitor from the collector to the emitter of transistor Q4. The local oscillation signal appearing at the collector of transistor Q4 is applied to the base of transistor Q5 by capacitor C1. The power source is a constant current source, and its configuration may be arbitrary. Q+o
is a current supply transistor, and constitutes a current mirror circuit with a transistor Q1 connected in series to a constant current source.

The voltage between the base and emitter of the transistor Q9 is also applied to the transistor Q3 via the resistor R2.

In the conventional frequency conversion circuit shown in Figure 1, the transistor Q
When a strong input signal enters the base of transistor Q1, it passes from the base of transistor Q1 to the emitter of transistor Q1.
The input signal is applied to the local oscillation circuit through the capacitance between the collector and base of No. 3 and the capacitor C1, and the input signal is mixed into the local oscillation signal, making it unstable.

The present invention is intended to eliminate such drawbacks and provide an excellent frequency conversion circuit with a simple configuration. That is, the frequency conversion circuit of the present invention has a separate emitter follower transistor Q5 on the collector side of the local oscillation circuit transistor Q4, as shown in an embodiment in FIG.
A local oscillation signal is applied from the emitter of transistor Q5 to the base of transistor Q6 via capacitor C1.

Therefore, according to the invention, the input signal is
Even if the emitter voltage of transistor Q5 changes, l・
Since the emitter impedance of transistor Q5 is low, the input signal is attenuated, and since the amount of current sent from the emitter to the base is reduced, it is extremely unlikely that the input signal will mix into the local oscillation circuit and cause it to become unstable. It has the advantage that oscillation operation can be expected and stable frequency conversion can be performed even when a large input signal is received.

Note that the transistor Q+2 is a transistor for supplying current to the 1-transistor Q5.

FIG. 3 shows another embodiment of the invention. In the embodiment shown in FIG. 3, additional transistors Q6, Q7 . QH, 0,8, resistor R5 is added and capacitor C1 is discarded.

In the embodiment shown in FIG. 3) - active 1'l of transistor
The contact potential vBE between the base and emitter in the Ji region usually varies by about 0.6v to 0.8v and is almost constant.

The power supply voltage is vo. Then, the base DC potential of transistor Q6 is vo. From 1 − vB of Runcisstar Q1+
Since it is the value minus E, it is almost vo. -vBK.

The shift force means that the base potential of transistor Q5 is also approximately vo.
. -vBE. On the other hand, the base of transistor Q5 is connected to vo through coil 7uL2. Since it is connected to the power supply, the DC potential is approximately V. . be equivalent to.

Therefore, the emitter voltage of transistor Q5 is approximately vo. -vBE. That is, the DC potential of the base of transistor Q3 and the DC potential of the emitter of transistor Q5 are approximately equal. Therefore, the voltage drop across the resistor R5 is extremely small, and the base potentials of the transistor Q6 and the base potential of the transistor Q5 are approximately equal, and the transistors Q, S, and Q3 operate differentially. Therefore, the local oscillation signal is applied to the base and emitter of transistor Q5 through resistor R3 to the base of transistor Q3, and is further applied to the collector of transistor Q3 through retransistor Q1. In addition to the emitter of Q2, there will be a ray.

The embodiment shown in FIG. 3 eliminates the capacitor C1 of the embodiment shown in FIG. 2 and uses a resistor R3 for DC coupling, which is extremely advantageous when integrated into an integrated circuit. Further, in the embodiment shown in FIG. 3, the local oscillation signal is transmitted to the transistor Q5.
In order to reduce the signal level applied to the base of
4 may be provided and divided by the resistor R4. However, since the emitter follower transistor Q5 is provided as in the embodiment shown in FIG. 2, there is an advantage that the human input signal is less likely to flow back into the local oscillation circuit.

In the embodiments shown in FIGS. 2 and 3, the intermediate frequency signal is taken out from the collector of the transistor Q1, but the intermediate frequency signal may be taken out from the collector of the transistor Q2.

As explained above, the present invention can provide a frequency conversion circuit that is stable even when a strong input signal is applied, and also eliminates the need for a coupling capacitor and provides an excellent frequency conversion circuit that is easier to integrate. can.

[Brief explanation of drawings]

FIG. 1 is an electrical connection diagram of a conventional frequency conversion circuit, and FIGS. 2 and 3 are electrical connection diagrams of respective embodiments of the frequency conversion circuit of the present invention. vo.・・・・・・Power terminal, engineering. ...Signal input terminal, Out...Frequency conversion output terminal, ■...
...constant current source, vCl, vo2...variable capacitor, L+, L2...coil/l/, TI
・・・・・・Transistor, Ql, Q2・・L for mixed circuit・Lansistor, Q3・・・・Transistor for current bias of mixed circuit, Q′・・・・Transistor for local oscillation, Qs ・River... Transistor for emitter follower, Q61Q++... Transistor for setting DC potential, Q, 7. Q8゜Q9, Q10, Q
+2 ・Old...Transinutor for current bias, Qls
...Transistor for input signal amplification, cl... mark: coupling capacitor, 02, 03: old... feedback capacitor. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 3

Claims (2)

[Claims] (1) First. a differential amplifier in which the emitters of the second transistor are coupled together; Connect the collector of a third transistor to the emitter of the second transistor, apply an input signal to the base of the first transistor, apply a local oscillation signal to the base of the third transistor, and connect the first transistor to the second transistor. The configuration is such that an intermediate frequency signal is taken out from the collector of the fourth local oscillation transistor, and the local oscillation signal is added to the base of the fifth emitter follower transistor from the collector of the fourth local oscillation transistor, and from the emitter of the sixth transistor to the third one. A frequency conversion circuit characterized by being added to the base of a transistor. (2) Connect the emitter of the sixth transistor to the emitter of the third transistor; The emitter of the sixth transistor is connected to the collector of the seventh transistor for current supply, and the emitter of the fifth emitter follower transistor and the base of the third transistor are connected in a direct current manner. Claim 1 characterized in that the base is configured to add a local oscillation signal to the base.
Frequency conversion circuit described in section.