JPH0319511A - Differential output interface circuit - Google Patents

Abstract

PURPOSE:To evade a change in the gain of a transistor(TR) for inverse amplification with a load connecting to a noninverting output terminal by providing the inverting amplifier TR and a differential output TR giving a noninverting output separately. CONSTITUTION:An inverting amplifier emitter follower TR 11 inverts (gain-1) a high frequency signal V1 outputted from an amplifier 2 and gives its collector output to a base of a 1st differential output emitter follower TR 12. Thus, an inverting output V2 is obtained at the emitter of the 1st differential output emitter follower TR 12. On the other hand, a 2nd inverting amplifier emitter follower TR 13 is connected in parallel with the TR 11 and a noninverting output V3 is obtained from the emitter of the TR 13. Thus, the gain of the TR 11 is not changed by the load at the noninverting output V3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an interface circuit used for processing output signals of high frequency amplifiers used in optical communications and the like.

[Conventional technology]

Conventionally, integrated circuits (ICs) constituting this type of single-width device have two types of output. One is a single input/l11 one output type, and the other is a differential input/differential output type. As the former, for example, NEC Corporation's μPC 1. 6
5 1 to 1656, the latter being NE592 and NE5 of Signetics (Slgnetlcs).
In any case, if the input is single, the output is also single, and if the output is differential, the input is also differential.

In this way, the conventional high-frequency amplification IC has a single output as long as it has a single input, so the output signal is vulnerable to external noise. For this reason, it was necessary to provide some kind of barrier at the output end.

On the other hand, there is a method of making the output differential using an interface circuit as shown in FIG. In the figure, an interface circuit 1 includes an emitter follower transistor A for inverting amplification and differential output whose base input is a high frequency signal V1 output from an amplifier 2, and an emitter follower transistor A whose base input is the collector output of this transistor A. An emitter follower transistor B for dynamic output is provided, and an inverted output V 1 is obtained as the emitter output of the transistor 1B, and a non-inverted output V3 is obtained as the emitter output of the transistor IA.

[Three problems to be solved by the invention] By using an interface circuit in this way, it is possible to differentiate a single output and strengthen the resistance to external noise. However, the conventional interface circuit described above can There is a problem in that the gain of transistor A shifts due to the influence of the load connected to the non-inverting output (V3) terminal, that is, the emitter terminal of transistor A. Also, resistors IC, ID, and I are used for gain and phase optimization.
It was inconvenient to adjust the resistance of E [R, R, R].

[Means to solve the problem]

The present invention provides an emitter follower transistor for inverting amplification whose base input is a single output high frequency signal from an amplifier;
In addition to the first differential output emitter follower transistor whose base input is the collector output of this transistor,
A second differential output emitter follower transistor is provided in parallel with the inverting amplification emitter follower transistor, and a variable resistor is connected to the base input terminal of the first or second differential output emitter follower transistor. This is what I did.

[Operation] An inverted output is obtained as the emitter output of the first differential output emitter follower transistor, and a non-inverted output is obtained as the emitter output of the second differential output emitter follower transistor. By separating the inverting amplification transistor, which used to be used for both purposes, and the differential output transistor, which provides a non-inverting output, into separate transistors, the load connected to the non-inverting output terminal allows the inverting amplification transistor to be Interest? 1} can be avoided from changing.

Furthermore, by adjusting the resistance value of the variable resistor, the phase difference between the inverted and non-inverted outputs can be freely adjusted to A.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to FIGS. 1 and 2 of the accompanying drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention. In the figure, the inverting amplification emitter follower transistor 1l inverts (gain -1) the ρ; frequency signal V1 output from the amplifier 2, and sends its collector output to the base of the first differential output emitter follower transistor 12. Enter. As a result, an inverted output V2 is obtained at the emitter end of the first differential output emitter follower transistor 12. On the other hand, for the high frequency signal v1, a second inverting amplifying emitter follower transistor 13 is connected in parallel with the transistor 11, and the non-inverting output V3 is drawn out from the emitter end of the transistor 13 instead of the transistor 11. Therefore, the gain of the transistor 11 does not change due to the load (not shown) applied to the non-inverting output (v3) terminal, and the gain can be set to -1 by setting the resistance values R and -R2 of the resistors 14 and 15. , this can be held stably.

Also, a variable resistor 1 is connected to the base input terminal of the transistor 13.
6 has been inserted. This variable resistor 16 arbitrarily delays the phase of the high frequency signal 1 and adjusts its resistance riRp to freely adjust the phase difference between the non-inverted outputs V, L and therefore V2 and V3. I can do it.

Similarly, from the viewpoint of gain and phase, resistor 17.
The resistance value R of 18, R is 3 to R - R
4 3 4 It has been set.

In this way, the single output obtained from amplifier 2 is V,
It is converted to a differential output consisting of V3 and is strengthened against external noise.

In Figure 2, the ambient temperature is 27°C and the power supply voltage is V. 0-4.8V
An example of the results of investigating how the phase difference between ■2 and ■3 changes depending on the resistance value R under the conditions shown below is shown below. From the same figure, the phase difference of the differential output is R
It can be seen that the adjustment can be made easily with just one value.

p Also, in a similar circuit, when a parallel circuit of a 59F capacitor and a 300Ω resistor was connected as a load to each of the V and ■ ends, almost no difference was observed in the gain of the transistor 1.

The phase difference between V2 and V2 can be adjusted in the same way by inserting a variable resistor into the base input terminal of the transistor 12 and changing the phase of V2.

Further, when this interface circuit itself is integrated into an IC, only the variable resistor 16 is externally attached, and phase adjustment can be easily performed from the outside.

〔Effect of the invention〕

As described above, in configuring an interface circuit that differentializes a single output high frequency signal from an amplifier, the present invention includes an inverting amplification emitter follower transistor whose base input is the high frequency signal, and whose collector output is used as the base input. a first differential output emitter follower transistor, a second differential output emitter follower transistor having an inverting amplification emitter follower transistor connected in parallel with respect to the high frequency signal, and these first or second differential output emitter follower transistors; By using a variable resistor inserted at the base input terminal of the output emitter follower transistor,
This has the effect of providing an interface circuit in which the inversion amplification gain is stable and the phase adjustment of the differential output is simple. If this is applied to a receiver in a high-frequency communication system such as optical communication, the receiver can be made smaller because there is no need to separately provide a barrier against external noise, and a stable received signal can be obtained. Furthermore, phase 2ffi of differential output can be easily performed and is extremely effective.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a diagram showing an example of the relationship between the resistance value of the variable resistor and the phase difference of the differential output, and Fig. 3 shows a conventional example. It is a circuit diagram. 1... Interface circuit, 2... Amplifier, 11.
・・Emitter follower transistor for inverting amplification, 12・
...first differential output emitter follower transistor,
13... Second differential output emitter follower transistor, 16... Variable resistor.

Claims (1)

[Claims] In a differential output interface circuit that differentiates a single output high-frequency signal of an amplifier and takes out a differential output consisting of inverted and non-inverted outputs, an emitter-follower transistor for inverting amplification that receives the above-mentioned high-frequency signal as a base input, and an emitter for this inverting amplification. The first transistor uses the collector output of the follower transistor as the base input and provides an inverted output as the emitter output.
a differential output emitter follower transistor, a second differential output emitter follower transistor which is connected in parallel with the inverting amplification emitter follower transistor for the high frequency signal and provides a non-inverting output as an emitter output; and a first or second differential output emitter follower transistor. A differential output interface circuit comprising a variable resistor inserted at the base input terminal of an emitter follower transistor for differential output.