JPS61242103A - Detecting circuit - Google Patents

Abstract

PURPOSE:To obtain the output of wave detection without using a capacitor for DC cut-off by driving a transistor which works with the bias voltage as a control circuit and controlling the working level of a transistor which performs the detecting action by the output voltage of an amplifier. CONSTITUTION:When the base of a transistor TR Q53 is set at a high level, the base of a TR Q54 is set at a low level. Then the TR Q53 and the TR Q54 are turned on and off respectively. When the outputs of both TRs Q51 and Q52 have phases adverse to each other, the base of the TR Q53 is set at a low level and the TR Q53 is turned off. While the base of the TR Q54 is set at high level and the TR Q54 is turned on. Therefore both TRs Q53 and Q54 detect the output signals having phases adverse to each other, and a detection current ID1 undergoes the full-wave rectification. Thus a DC cut-off capacitor can be omitted from a detecting circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a detection circuit, and is suitable for use in channel switching in which a meter is driven by a detection output.

[Background technology]

Figure 2 shows an example of a detection circuit for detecting electric field strength. 9 Publisher: Radio Gijutsu Co., Ltd., page 219).

The above detection circuit is well known to those skilled in the art, so to briefly describe it, Vin is the input signal, and the filter composed of resistor R1 and capacitors C3 to Cs removes AC components. It is something to do. Transistor Qi) Qt p Resistors R, Rm constitute the first stage amplifier 1, transistors Qa, Q4, R
4. Rs operates as a buffer circuit.

The output signal of the first stage amplifier 1 is transferred to the second stage amplifier 2 and the DC cut capacitors C, , C through the emitter resistor R4゜Rs.
, and to the detector 3.

The next stage amplifier 2 includes transistors Qs, Q and resistors R, , R
, and further amplifies the output signal. The transistors Qy, Qs, Re, and Re operate as a buffer circuit, and their output signals are supplied to the detector 4 via DC cut capacitors C, C4f.

The detector 4 performs detection between the pace and emitter of the transistor QstsQ*t, and the detected output is supplied to the pace of the transistor QrssQtq.

Also, since the transistor Qtsn Qs・ also performs detection, the transistor Q! Good Q! ,,resistance R1,,R1
! Two detected outputs are synthesized and appear from the current mirror circuit configured as follows. The detection output Vo corresponds to the strong electric field and is used to drive a field strength meter or as a channel switching signal. Note that the transistors Qms-Qst-resistors R, , R, . . . and the reference voltage Vref constitute a constant current circuit.

According to the inventors' study regarding the above-mentioned detection circuit, in order to obtain a high-level detection output, N (N is an integer) stages of amplifiers are required, and in order to synthesize the respective output signals, 2N stages of amplifiers are required for DC cut. capacitor is required. When this detection circuit is used in an FM receiver, the intermediate frequency signal is
Since the frequency is 0.7 MHz, a small capacity is sufficient.

However, in the case of an AM receiver, the intermediate frequency signal is 450K
Hz and the second intermediate frequency for car telephones is 455 KH.
Since there is z, a large capacity capacitor is required. The inventors have clarified that unless the capacitances of capacitors 01 to C4 are made sufficiently large, the detection characteristics will fluctuate due to variations in capacitance values.

On the other hand, considering the reduction in size and weight of electronic equipment, it is desirable that the detection circuit described above be also integrated. From this point of view, the 2N capacitors mentioned above become an obstacle to IC implementation.

Therefore, the present inventors conducted further technical studies in order to reduce the number of capacitors mentioned above. Then, they realized that the number of capacitors described above could be reduced by utilizing the voltage difference caused by the load resistance of the amplifier, and came to propose the present invention.

[Purpose of the invention]

An object of the present invention is to provide a detection circuit that can obtain a detection output without using a DC-cut ninth capacitor and can be easily integrated into an IC.

The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings.

[Summary of the invention]

Overview of the invention disclosed in this application! Briefly stated, it is as follows.

That is, a bias circuit consisting of resistors R1 and R64 is provided on the output side of the amplifier 11, and the bias voltage drives the transistor Qsw which operates as a control circuit, and the operation of the transistor QsssQ14 which performs all detection operations using the output voltage of the amplifier 11. This achieves the object of the present invention, which is to control the level and obtain a detected output without using a DC cut capacitor.

〔Example〕

Hereinafter, an embodiment of a detection circuit to which the present invention is applied will be described with reference to FIG.

The feature of this embodiment is that a DC cut capacitor is not required when the detection output is obtained from the output signals of two amplifiers and combined.

Resistors R, , connected in series with transistors Q□, Q□
, R■, and further resistors R,,,R,, are the first stage amplifier 11t
- Configure. The resistance R,,,R,, is connected to the AC GNDt
-It is for making.

Here, when comparing points A and B, the transistor Q□
,QI! When the resistors R1 and R1 turn on and off, their phases become opposite to each other (180°).

Since the midpoint of R84 is at 0 potential, the transistor Qss
The pace of will be ACGND. Note that the resistance value is R1
=R□, R□=Rss, and R55=Rh.

Furthermore, the DC biases at point A, point B, and transistor Qss are the same. Therefore, the offset voltage of the transistors Qss and QI4 connected to the differential pair, and the voltage of the transistor Qsa#Q@11 are determined.

The pace of transistor Qia, or transistor Q
When a signal having a higher level than the offset voltage is inputted at a pace of s4, a detection current IDt flows through the transistor Q2 constituting the current mirror circuit.

That is, the pace of transistor Qss becomes low level, the pace of transistor Qa 4 becomes low level, and the pace of transistor Q11. turns on and transistor Qs4 turns off. On the other hand, when the output of transistor QitsQat is in opposite phase, transistor Q. The pace of transistor Qs4 goes low and turns off, and the pace of transistor Qs4 goes high and turns on. Therefore, the transistor QsssQs4 detects output signals having opposite phases to each other, and the detection current IDt becomes a current that is a combination of both signals, that is, a double-wave rectified current.

If the current Io determined by the constant current circuit 13 is set as Rsx<R1, then the gain of the amplifier 11 is 0R due to Io (Rss +R1!)
II is determined, and the offset voltage is determined as 2. Then, the gain and detection characteristics become 1:1, and fluctuations in the detection characteristics are reduced.

Note that the two-stage amplifier 12 has exactly the same circuit configuration as the first-stage amplifier 11 described above. Therefore, the first stage amplifier 1
Based on the output of 1, the two-stage amplifier 12 operates in the same manner as described above, and the detection current IDt flows.

As a result, two detection currents I DI j I DI flow through the transistor Q s s , and the output from the two transistors Q s .

The same current flows through the load resistor R6t. Since the voltage drop across the resistor R6° is large, the load can be sufficiently driven by the detected output Vo obtained from the third terminal, and is also double-wave rectified.

Note that transistor Qst, Qet>resistance R6! ~
Rss Ia constitutes a negative feedback circuit, and capacitor C0~
CtS is for removing alternating current components.

In addition, the transistor Q□~Qyjj resistor RSS~R61
The specific current circuit 13 is composed of a current generator as described above. stipulates.

By the way, the resistors Rm and RA' in the above detection circuit are used for range adjustment IEt-, and the detection current IDtp
When adding Int k, the addition position is finely adjusted. This resistance R, RA/ reduces the deviation when weighing the detection current IDI) Int.

〔effect〕

(1) Obtain output voltages with opposite phases from the load circuits of the amplifiers that amplify the input signal, obtain a detection current for each output of each phase, and offset the output voltages with the opposite phases to generate an AC signal. Since the configuration is configured to obtain a grounded bias voltage and regulate all of the above detection current, the bias voltage can be set without using a DC cut capacitor, and a detection circuit with reduced DC cut capacitors can be obtained. This effect can be obtained.

(2) By providing a plurality of detectors as described in (1) above and combining their detection currents, a detection output with a large amplitude and a wide dynamic range can be obtained.

(3) The above (1) makes it easy to integrate the detection circuit into an IC.

(4) Since a range adjustment means is provided for the multiple detection circuits shown in (1) above when combining the detection currents, the nonlinearity of the combined detection currents can be reduced and the dynamic range can be widened. This effect can be obtained.

(5) In addition to the above (1), since the frequency-dependent capacitor can be removed, it is possible to obtain the effect that the entire frequency range to which the detection circuit is applied can be expanded.

(6) Since the gain of the amplifier and the amplitude of the output voltage can be set at t-1:1, it is possible to reduce fluctuations in detection characteristics.

Although the invention made by the present inventor has been specifically explained based on Examples above, the present invention is not limited to the above Examples and can be modified in various ways without departing from the gist thereof. Needless to say.

For example, one of the transistors QsssQI4 can be deleted to provide a half-wave output.

[Application field]

In the above description, the invention made by the present inventor has mainly been explained with reference to the detection circuit, which is a field in which the invention is useful, but the invention is not limited thereto.

The present invention can be used at least in various radio receivers and wireless communication devices that require electric field strength.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an embodiment of a detection circuit to which the present invention is applied, and FIG. 2 is a circuit diagram of nine detection circuits that were studied prior to the present invention. 11.12... Amplifier, 13... Constant current circuit, Qs
1~Q? l...transistor, R11 to R6
,...Resistance, Rm, Rm'...Range adjustment resistance, W
im...input signal, Vo...detection output, IDt p
IDt detection current.ゝ・１、-ノ. Figure 2 C

Claims (1)

[Claims] 1. A detector that obtains a detection output based on output voltages in opposite phases appearing on the output side of the amplifier 2, and a detector that cancels out the output voltages in opposite phases to become zero potential in terms of alternating current. 1. A detection circuit comprising: a bias circuit that obtains a bias voltage; and a control circuit that controls an operating level of the detector using the bias voltage. 2. The detection circuit according to claim 1, wherein the detection circuit includes a plurality of detection circuits, and the detection outputs of each detection circuit are synthesized.