JPH02260808A - High speed programmable gain amplifier - Google Patents

Abstract

PURPOSE:To attain high speed input changeover and independent phase compensation of each input circuit by providing 2 sets each of current switch differential amplifier circuits to the collector of a transistor(TR) being a component of a differential input circuit so as to switch a current of the differential amplifier circuit to a power supply or the output. CONSTITUTION:Current switch circuits Q21, Q22, Q24 and Q25 are provided to collectors of differential input circuits Q23, Q26 to cause a current not selected to flow to a power supply (+Vcc), and since the differential input circuits Q23, Q26 are not turned off, the on-time is lost, the switching time is decreased, then the processing speed is quickened. Since the differential input circuits Q23, Q26 are provided independently of each input, the phase is compensated independently of the input circuit and optimum phase compensation as to each input is attained.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a high-speed programmable gain amplifier, and more particularly to a high-speed programmable gain amplifier whose inputs are switched at high speed.

(Prior Art) A programmable gain amplifier (abbreviated as PGA) has at least two sets of gain amplifiers built-in, and one set of gain amplifiers is selected by an external switching signal, and the amplifier is set to a predetermined value. The gain is set to .

FIG. 4 is a block diagram showing the general configuration of an A/D conversion system using PGA. A PGAI with a gain of ×1 and a gain of ×2 and a PGA2 with a gain of ×4 and a gain of ×8 are connected in series, and the output of PGA2 is A/
The configuration is such that it enters the D converter 3. These PGAI,
The PGA 2 is configured to be able to select one of two sets of gain amplifiers by a switching signal from the outside.

Therefore, in the system shown in the figure, X4
．． X8. Three types of gains for X16 can be selected, and the A/D converter 3 always receives full-scale input.

FIG. 5 is a circuit diagram showing an example of a conventional configuration of a PGA. As is clear from the figure, PGAs are often realized by integrated circuits. The PGA shown in the figure has an input switching section 11. A input section 12. B input section 13. It is composed of a gain stage section 14 and an output section 15. The input switching unit 11 is a circuit for selecting one of the amplifiers A and B, and mainly includes transistors Q13 . Q14 and current source C8
It consists of 1.

Inside the eight are differential transistors Ql, Q2 . It is composed of a transistor Q5 and a current source CS4. Input section B includes differential transistors Q3. Q4゜Transistor Q
6 and current sources C33 and C34. As is clear from the figure, the current source CS4 is common to the A input section and the B input section. The gain stage section 14 includes transistors Q7. Q8゜Bias circuit 14A that supplies bias to these transistors and these transistors Q7. Q8
It is composed of current sources C82 and C33 that provide drive current to the circuits and a current mirror circuit. A terminal Comp to which a phase compensation capacitor is connected is also included in the gain stage section 14. Transistor Q7 forming the gain stage
．． The collector outputs of the A input section 12 and the B input section 13 are commonly input to Q8. The output section 15 is a so-called diamond buffer circuit, and includes transistors Q9 to Q1.
2 and current source CS5. It is composed of C86.

Output Out is complementary circuit transistor Q
11. It is taken out from the connection point of Q12.

As is clear from the above configuration, the gain stage section 14
The output section 15 is common to amplifiers A and B.

In the circuit configured in this way, the input switching section 11 gives a selection signal to either amplifier A or amplifier B. For example, when a select signal from amplifier A is applied, transistor Q13 is turned on. When 013 is turned on,
A input section turns on. With the internal circuit 12 turned on, a differential input signal is input to the bases of the transistors Ql and Q2.

The collector output of the A input section 12 is converted into a single-ended signal by the gain stage section 14.

The output of the gain stage section 14 enters the output section 15, where it is current-amplified and then output from the output terminal Out.

(Problem to be Solved by the Invention) In the conventional circuit, transistor Q5. Input part A in Q6
, H, the current flowing through the current source C34 is switched (current switch operation). In such a current switch operation, transistor Q5. It is necessary to discharge the charge accumulated in the collector capacitance on the turned-off side of Q6. Therefore, high-speed switching cannot be achieved unless a separate discharge circuit is provided. This collector capacitance also deteriorates the isolation of each input circuit.

Furthermore, since the gain stage section 14 and the output section 15 are shared, there is a problem in that optimal phase compensation cannot be performed separately for the amplifiers A and B.

The present invention has been made in view of these problems, and its purpose is to provide a high-speed programmable gain amplifier that can perform input switching at high speed and perform phase compensation independently for each input circuit. The purpose is to

(Means for Solving the Problems) The present invention, which solves the problems described above, provides a programmable gain amplifier that includes at least two sets of gain amplifiers and selects one of them using an external switching signal. In the amplifier, as many differential input circuits as the number of inputs are provided to receive each input, and two sets of current switch differential circuits are provided on the collector side of the transistors constituting the differential input circuit. One of the collectors is used as a power supply and the other as an output, and an input switching signal is applied to the bases of these differential circuit transistors to switch the current of these differential circuits to the power supply or output.

(Operation) Input switching is performed on the collector side of the transistors forming the differential input section. In addition, this input switching section uses transistors with a differential configuration, so that the amplifier output on the side that is not used is released to the power supply side. With such a configuration, high-speed switching can be performed. Furthermore, since the emitter circuit can be designed freely, phase compensation can also be performed independently depending on the circuit.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is an electrical circuit diagram showing the configuration of essential parts showing an embodiment of the present invention. In the figure, only the input switching circuits of amplifiers A and B are shown, and the gain stage section and output section are not shown. It is assumed that the configurations of the gain stage section and the output section are similar to the circuit shown in FIG. In the figure, 20.21
are two sets of differential input sections. These differential input sections 20.2
1, the lower stage is a differential transistor Q23. Q26 and Q2
9, a differential input circuit using Q32, and the upper stage is a transistor Q21. Q22, Q24. Q25, Q27゜Q28, Q
30. Q31 constitutes a current switch circuit.

Transistor Q21. Q22 and transistor Q24.
The emitters of Q25 are connected in common. Transistor Q21. The common connection point of Q22 is the transistor Q
A transistor Q24.23 is connected to the collector of the transistor Q24. The common connection points of Q25 are respectively connected to the collectors of transistors Q26.

Also, transistor Q21. A switch signal S2 is applied to the base of transistor Q22. A switch signal S1 is connected to the base of each Q25.

Also, transistor Q21. Q24 collector is power supply +
They are commonly connected to Vcc, and the collector of the transistor Q22 becomes the output 0UT1, and the collector of the transistor Q25 becomes the output 0UT2. A current source C810 is connected to the emitter of transistor Q23, and a current source C5IO
The other end is connected to the power supply -Vcc. A current source C811 is connected to the emitter of the transistor Q26, and the other end of the current source C811 is connected to the power supply -Vcc. Furthermore, transistor Q23. A phase compensation resistor Rd is connected between the emitters of Q26.

The configuration of the differential input section 20 described above is exactly the same for the current switch circuit and the differential input circuit of the differential input section 21. However, in the differential input section 21, the differential input circuit transistor Q29. The emitters of Q32 are commonly connected, this common connection point is connected to one current source C312, and the other end of current source C812 is connected to the power supply -Vcc. The operation of the circuit configured as described above will be explained as follows.

Here, circuit A is used at x1, and circuit B is used at x3.
2 (actual gain setting is done using an external resistor). First, circuit A.

The phase compensation of B will be explained. Generally, the smaller the gain, the larger the amount of phase compensation. Therefore, no special phase compensation is performed on the circuit B side, which is in charge of the large gain x32 (actually, a capacitor is connected to the phase compensation terminal of the gain stage section for light phase compensation. Fig. 5 reference). On the other hand, since the gain on the circuit A side is ×1, it is necessary to perform phase compensation. According to the present invention, the current source can be configured to also serve as phase compensation.

For ×1, the day generation (current source) is C3
It is divided into two parts, lO and C3lI, and a resistor Rd is connected between them. With this configuration, the mutual conductance gm is lowered, the phase margin in the Bode diagram is increased, and the circuit is stabilized.

As described above, according to the present invention, since the differential input circuit is provided independently for each input, phase compensation can be performed independently for each input circuit, and optimal phase compensation can be performed for each input. be able to.

Next, the operation of this circuit will be explained with reference to the timing chart shown in FIG. Figure 2 (a).

As shown in (b), when the switch signal S1 is “1” and S2 is “0”, the transistor of the current switch circuit is Q22.
．． Q25. Q28. Q31 is turned on and Q21. Q2
4. Q27. Q30 is off. At this time, among the transistors that are turned on, Q22. Q25 is 0UTI, 0UT2 as shown in (1) (that is, circuit A side potion)
is output as Since the turned-on transistors Q28 and Q31 on the circuit B side are connected to the power supply +Vcc, current flows to the power supply +Vcc side on the B side.

Next, as shown in (a) and (b), the switch signal S1
is "0" and S2 becomes "1", the transistor of the current switch circuit becomes Q21. Q24゜Q27. Q30 is on, Q22. Q25. Q28 and Q31 are turned off.

At this time, among the transistors that are turned on, Q27.
Q30 (that is, circuit B side) is 0U as shown in (c)
Output as TI, 0UT2. Transistor Q21. turned on on the circuit A side. Since Q24 is connected to the power supply +Vcc, current will flow to the power supply +Vcc side on the A side.

Transistor 023. Q26 and current source C3lO, C3
lI constitutes a differential input circuit on the A side, and transistor Q2
2. When Q25 is on, the output is sent to the next stage. Similarly, transistor Q29. Q32 and current source C812 constitute a differential input circuit on the B side, and transistors Q27. When Q30 is on, the output is sent to the next stage. Thus, in the present invention, transistor Q23. Q26 and Q29. Since the differential input circuit consisting of transistors Q32 is always on, no current switching takes place in this part and the transistors Q23.
Q26 and Q29. The collector capacitance of Q32 no longer affects the switching time. Therefore, the switching time in the present invention is the same as that of transistor Q21. Q22.
Q24. Q25゜Q27. Q28. Q30. High-speed switching is possible depending only on the switching time of Q31.

FIG. 3 is an electric circuit diagram showing an example of the main part configuration of another embodiment of the present invention. Components that are the same as those in FIG. 2 are designated by the same reference numerals. In the figure, current sources C810 to C312 are composed of transistors and resistors as shown in the figure.

A bias voltage VM is applied to the base of the transistor constituting the current source. Power supply shown in Figure 2-
Vcc is shown here as VEE. The biggest difference compared to the embodiment shown in FIG. 2 is the transistor that constitutes the current switch circuit, with outputs of
Q22. connected to Q22. Q25. The point is that the bias voltage VP is fixedly applied to the bases of Q27 and Q30.

Transistor Q21 . connected to power supply Vcc.
Q24. Q28. Switch signal SL to the base of Q31,
S2 is applied.

The inputs of circuit A are INI and IN2, and the inputs of circuit B are rN3.
．． It is IN4. Further, a phase compensation capacitor C is connected in parallel to the resistor Rd.

In a circuit configured in this manner, even when the power supply VcC is relatively low (for example, +5V), current can be sent to the next stage without saturating the transistor connected to the output. In addition, by using this connection method,
It is possible to prevent noise from being added to the output. The other operations are the same as those in FIG. 2, so the explanation will be omitted.

In the above explanation, the case where two sets of input circuits A and B are provided, but the present invention is not limited to this.
Three or more sets of circuits can be provided, and one circuit can be selected by switching these circuits. Further, in the above explanation, the case where the phase compensation is provided only on the Yakaji side is taken as an example, but the present invention is not limited to this, and it is also possible to provide it on the B side, and also on the A side, It is also possible not to provide it on any of the B sides.

(Effects of the Invention) As described above in detail, according to the present invention, the current switch circuit is provided on the collector side of the differential input circuit, and the current on the non-selected side is made to flow to the power supply (+Vcc). , since the differential input circuit does not turn off, there is no turn-on time, resulting in shorter switching times and faster speeds. Furthermore, since separate current sources are provided on the emitter side of the differential input circuit, optimal phase compensation can be performed in each current source.

[BRIEF DESCRIPTION OF THE DRAWINGS] Fig. 1 is an electric circuit diagram showing the configuration of main parts showing one embodiment of the present invention, Fig. 2 is a timing chart showing the operation of each part, and Fig. 3 is an electric circuit diagram showing the configuration of main parts showing an embodiment of the present invention. FIG. 4 is a block diagram showing the general configuration of an A/D conversion system using PGA; FIG. 5 is a circuit diagram showing a conventional configuration example of PGA. It is. 20.21...Differential input section

Claims (1)

[Claims] In a programmable gain amplifier that has at least two sets of gain amplifiers built-in, one of which is selected by an external switching signal,
The number of differential input circuits that receive each input is equal to the number of inputs, and two sets of current switch differential circuits are provided on the collector side of the differential transistors constituting the differential input circuit. Power one side of the collector,
A high-speed programmable gain amplifier configured to have the other output as an output, apply an input switching signal to the bases of these differential circuit transistors, and switch the current of these differential circuits to a power supply or an output.