JPH04119011A - Semiconductor device - Google Patents

Abstract

PURPOSE:To quicken the falling of an output of an emitter follower output stage without incurring increase in power consumption by increasing a current of a current source of an emitter follower whose output falls down and decreasing a current of a current source of an emitter follower whose output rises. CONSTITUTION:When an output X changes from H to L and an output Y changes from L to H, a current in a path comprising diodes D2, D4 and a resistor R6 is increased and a current in a path comprising diodes D1, D3 and a resistor R7 is decreased, a transistor(TR) T6 is conductive deeper, then the current of the current source is increased and a TR T7 is less conductive, then the current of the current source is decreased. Thus, the falling of the output X is steep and the output Y is promoted. When the output X changes from L to H and the output Y changes from H to L, the current in the path comprising diodes D2, D4 and the resistor R6 is decreased and the current in the path comprising diodes D1, D3 and the resistor R7 is increased, the TR T7 is conductive deeper to make the falling of the output Y steep. Moreover, the TR T6 is less conductive to promote the rising of the output X. Thus, the power consumption is reduced more than the case with increasing currents of both the current sources.

Description

[Detailed Description of the Invention] (Summary of the Invention) An object of the present invention is to speed up the falling edge of an emitter follower output stage without increasing power consumption in a semiconductor device, particularly an emitter follower circuit with high speed operation and low power consumption. In a semiconductor device comprising an ECL circuit main body and a pair of emitter followers at its output stage, upon receiving the outputs of the pair of emitter followers, the current of the current source of the emitter follower on the side where the output falls is increased, and the output rises. The configuration includes a control circuit that reduces the current of the side emitter follower.

[Industrial application field]

The present invention relates to a semiconductor device, particularly an emitter follower circuit that operates at high speed and consumes low power.

2. Description of the Related Art In recent years, as systems have become faster and more highly integrated, there has been a demand for semiconductor circuits (LSIs) that are faster, more integrated, and have lower power consumption.

[Conventional technology]

ECL circuits are often used in high-speed LSIs, and a conventional example of the ECL circuit is shown in FIG.

T, , T are npn) transistors forming a differential pair, R
3-R2 is the load resistance, T, and R4 are the npn) transistor and resistor that constitute the constant current source.

These constitute the main body of the ECL. T, ,T, is np
The nl-transistors, T6 and R1, and T7 and R7 are npn transistors and resistors that constitute a constant current source, and these T, and T, and R6, T, and T, and R6 constitute an emitter follower. Transistor T"4."T゛.

The base receives the output from the ECL main body, and the output ends X and Y of the emitter follower become the output ends of this circuit.

C, , C, is the capacitance attached to the output wiring.

Differential power, I) is added to the base of the differential pair transistors T, , T, and if D > 100, T1 is on, T2 is on,
Output X is high, and output Y is high. Conversely, if D is T, off, T2 is on, output X is H1, output Y is L.

When the output X changes from L to H, the wiring capacitor C1 is charged. Correctly, the output X changes from L to H as the wiring capacitance CI is charged.
However, CI is charged by the low-resistance transistor T.
4, so it is fast. Output X is H-L
When the voltage changes to , the wiring capacitance C1 is discharged. Correctly, the output X falls from H to L with the discharge of the wiring capacitance C1, but
This discharge occurs through the constant current source T&1R5, which is slow due to its high resistance (the output current of the constant current source is small). This tendency increases as the wiring capacitance C1 increases and as the current of the constant current source decreases. The same applies to the output Y.

[Problem to be solved by the invention]

In a conventional ECL circuit, in order to speed up the H-L fall of the output, it is possible to increase the current of the constant current source (emitter follower current), but this constantly flows, leading to an increase in power consumption ( .

The object of the present invention is to improve the above points and to speed up the fall of the emitter-follower output stage without increasing power consumption.

[Means to solve the problem]

As shown in FIG. 1, in the present invention, a control circuit receives the outputs X and Y of a pair of output stage emitter followers, controls the current of the current source of the emitter follower on the other side, and increases the current when the output falls. A CCT will be provided.

As in all figures, parts that are the same as in other figures are given the same reference numerals. Output stage emitter follower current source T6
and R5, T7 and R6 are the current source T3 of the differential pair in FIG.
and the same constant voltage as R4 ■. .

A constant current source is constructed based on the voltage given by the constant voltage ■
. , only the current sources of the differential pair receive the output of the control circuit CCT.

[Effect]

In this circuit, when the output X falls from H to L, the output Y rises from L to H. Using this, the control circuit OCT raises the base potential of the transistor T, and the current source T b,
Increase the current of Rs. Therefore, the output X falls quickly.

The same is true when the output Y falls from H to L. At this time, the output X rises from L to H. The control circuit OCT uses this to raise the base potential of the transistor T, and the current source T?
, increase the current in R6. Therefore, the output Y falls rapidly.

When output X falls and output Y rises, current sources Th and R
Although the current of s becomes large, the current of current source T7R6 becomes small at this time. When the output Y falls and the output
The currents of i, , and Rs become small.

In other words, the current of the current source with the H side output is small, and the current of the current source with the L side output is large. Therefore, compared to increasing the current of both current sources, the power consumption can be reduced.

[Example] FIG. 2 shows an example of the present invention. In this example, the control circuit OCT is composed of CCT and CCT2, CCT1 is composed of a series circuit of diodes DI, D3 and resistor R7, diode D1 is inserted between emitter follower transistors T4 and I6, and diode 'D3 and The resistor R7 is connected in series between the connection point a of I6 and the low potential power supply ■, and the connection point of D3 and R1 is connected to the base of the current source transistor T of the emitter follower on the other side. Ru.

The control circuit CCT also has a similar configuration.

To explain the operation, when the output X changes to HL and the output Y changes to 1--H, the current in the path Dz, Da, R, l becomes large, D,, D3. The current in the path R becomes small, transistor T increases its conductivity and the current of this current source becomes large, and transistor T decreases its conductivity and the current of this current source becomes small. Therefore, the fall of the output X becomes rapid, and the rise of the output Y is also promoted.

Conversely, when the output X changes to L-H1 and the output Y changes to HL, D2. D,, the current in the RB path is small, D1D3. R
The current in path 7 becomes large, transistor T increases its conductivity and the fall of the output Y becomes rapid, and transistor T6 decreases its conductivity to promote the rise of the output X.

Figure 3 shows the diode D3. D- is replaced with resistors R9 and RIO, and the operation is the same as in FIG. 2.

To give an example of the numerical values of the circuit shown in FIG. 2, the L level of the outputs X and Y is -1,6■, and the H level is -1,0■. In other words, in this example, the high potential side power supply ■. . is ground, low potential side power supply■. is set to a negative potential (-5.2V). Current source T6
Let the currents of T7 and R5 be 11, and the currents of current sources T7 and R7 be I2, and when these become large, the diodes D+ and D
Assume that the voltage drop r of z is 0.85V, and conversely, when it becomes smaller, it is 0.8V.

In this state, when the output X changes to H-L, the note a
The potential of is -1,6V-0,85V=-2,45'V, /
-)" b (7) The potential is -1,0-0,8=-1
, 8V 2.

Assuming that the voltage drop across the diodes D, D, is 0.85 V when the current is large and 0.8 V when the current is small, the base of the transistor T is -1.8 V - 0,
85V=-2,65V, the base of transistor T7 is -
2,45V-0,8V=-3,25V.

In this way, the base potential of the transistor T6 becomes sufficiently higher than the base potential of the transistor T, and the current ■1 changes to the current I
2 (than at H level) (for example, I,
=1.4mA, Iz -0,75mA), wiring capacitance C1
The charge is rapidly extracted.

The current of the transistor T7 is smaller than that of the transistor T6 (when at L level), so that the rise of the output Y can be promoted and power consumption can be reduced.

The current flowing through the diodes D, D, can be very small since it is only necessary to turn on these diodes D, D4.
Therefore, no increase in current consumption occurs.

The diodes D and -D are for level shifting, and their presence requires only a small resistance to supply the required base potential to the transistors T and T7. Further, the diodes DI and Dz ensure that a normal voltage is applied between the bases and collectors of the transistors Tb and I7. For example, as shown above, node a
As mentioned above, when the voltage is -2,45 and the node b is -1,8, the base of I6 is 2,65 V, which is lower than the collector potential.

If the bases of T, excluding D2, are connected to the output terminal Y via a resistor, note a will be -1,6■, and the base of I6 will be -1,0■ at the highest, and the base will be higher than the collector. There is a risk of potential. At this point, the diode DI"' D
In FIG. 2, where the collector potential and base potential of the transistors T b and T'r are determined in step 4, a bias point can be set reliably.

Also, the glue in Figure 2 and R? , D4 and Rs, R9 and R in Figure 3? , R.I. and RIl are part of the emitter follower current (therefore, they are not extra currents for control that are not directly related to circuit operation), and contribute to the fall of the output when the output falls.

〔Effect of the invention〕

As described above, the present invention makes it possible to speed up the fall of the output without substantially increasing the emitter follower current, and greatly contributes to improving the performance of LSI.

[Brief explanation of drawings]

FIG. 1 is a principle diagram of the present invention, FIGS. 2 and 3 are circuit diagrams showing embodiments of the present invention, and FIG. 4 is a circuit diagram showing a conventional example. In FIG. 1, T, T2 are emitter-coupled transistors of the ECL body, T4, T, and R5, T. and T, and R6 are emitter followers, X and Y are their outputs, and C
CT is a control circuit. Figure 3: Circuit diagram showing a conventional example Figure 4

Claims (1)

[Claims] 1. In a semiconductor device comprising an ECL circuit main body and a pair of emitter followers at its output stage, the output of the emitter follower on the side where the output falls (X, Y) is received. A semiconductor device comprising a control circuit (CCT) that increases the current of a current source and decreases the current of an emitter follower on the side where the output rises. 2. The control circuit uses diodes (D_1, D_2) inserted between the emitter follower transistor and its current source.
), and diodes (D_3, D_4) connected between the connection point (a, b) between the diode and the current source and the low potential side power supply.
and a resistor (R_7, R_8) in series, and the series connection point of the diode and the resistor is connected to the base of the current source transistor (T_6, T_7) of the emitter follower on the other side. 1. The semiconductor device according to 1. 3. The control circuit uses diodes (D_1, D_2) inserted between the emitter follower transistor and its current source.
), and a first resistor (R_9, R_1_
0) and second resistors (R_7, R_8), and the series connection point of the first and second resistors is connected to the base of the emitter follower transistor (T_6, T_7) on the other side. The semiconductor device according to claim 1, characterized in that: