CN102723944B - A kind of method and circuit single-ended signal being converted to differential signal - Google Patents

Abstract

The invention discloses a method and circuit for converting a single-end signal into a differential signal, comprising a transimpedance amplifier, a high-pass filter, an AC coupling resistor, a DC bias circuit, a voltage stabilizing capacitor and a Schmitt trigger. The transimpedance amplifier is connected to the high-pass filter; the high-pass filter is connected to one input terminal of the Schmitt trigger; the voltage stabilizing capacitor is connected between the other input terminal of the Schmitt trigger and the ground; between the two input terminals of the Schmitt trigger; the DC bias circuit is connected between the two outputs of the Schmitt trigger, and is used to provide a DC working voltage for the two input terminals of the Schmitt trigger, so that the Schmitt trigger The DC operating voltages at the two inputs of the flip-flop tend to be equal. The most obvious advantage of adopting the present invention is that it is suitable for both continuous mode transimpedance amplifiers and burst mode transimpedance amplifiers.

Description

A method and circuit for converting single-ended signals into differential signals

technical field

The invention relates to the field of electronic circuits, in particular to a method and a circuit for converting a single-ended signal into a differential signal.

Background technique

A transimpedance amplifier is an electronic circuit that converts a current signal into a voltage signal and amplifies it. One of its most common uses is as a preamplifier for optoelectronic receivers in optoelectronic communication technology. Transimpedance amplifiers used in optical communication signal receivers have two operating modes, namely continuous mode and burst mode. In the burst mode, the signal flow is discontinuous, there will be a pause between the two signals before and after, and the strength of each signal can have a relatively large difference. Burst-mode functional requirements are a new challenge for transimpedance amplifiers. At the same time, with the increase of the speed of the optical communication network, the electrical signal converted from the optical signal generally needs to be in a differential form. The requirement that the output signal be in differential form is another challenge in the design of burst-mode transimpedance amplifiers.

The electrical signal generated by the optical signal converted by the photodiode and amplified by the transimpedance amplifier is generally a single-ended non-differential signal. Single-ended signals contain two parts, DC and AC. Among them, the AC part carries communication information, while the DC part is only related to the structure of the amplifier and has nothing to do with the communication signal. The differential signal generally only contains communication information, and its DC part is approximately zero. Converting a single-ended signal to a differential signal is usually done using a DC restoration circuit. The function of the DC restoration circuit is to use the negative feedback loop to generate a DC reference voltage equal to or similar to the DC component of the single-ended signal. At the same time, the single-ended signal and the DC reference voltage are connected to the input end of the differential amplifier, and the output signal becomes a differential signal. In the existing burst mode transimpedance amplifier, a negative feedback loop time constant selection switch S is added on the basis of the above DC restoration circuit structure to realize the differential output conversion function (as shown in FIG. 1 ).

Therefore, the prior art still needs to be improved and developed.

Contents of the invention

The purpose of the present invention is to provide a method and circuit for converting a single-ended signal into a differential signal, aiming at solving the problem that the existing transimpedance amplifiers in continuous mode and burst mode cannot be interoperable, and the transimpedance amplifier used in burst mode The impedance amplifier needs to add a negative feedback loop time constant selection switch on the basis of the DC restoration circuit structure to realize the differential output conversion function.

Technical scheme of the present invention is as follows:

A method of converting a single-ended signal to a differential signal, wherein,

First use the high-pass filter to eliminate the DC component in the single-ended signal; then use the AC coupling resistor to load the single-ended signal on the differential Schmitt trigger, and finally the differential Schmitt trigger is input according to the DC bias circuit at the input end. The DC working voltage tends to be equal to complete the differential conversion of the signal.

A circuit for converting a single-ended signal into a differential signal, which includes a transimpedance amplifier, a high-pass filter, an AC coupling resistor, a DC bias circuit, a stabilizing capacitor, and a Schmitt trigger. The transimpedance amplifier is connected to the high-pass filter; the high-pass filter is connected to one input terminal of the Schmitt trigger; the voltage stabilization capacitor is connected between the other input terminal of the Schmitt trigger and the ground; the AC coupling resistor is set at between the two input terminals of the Schmitt trigger; the DC bias circuit is connected between the two inputs of the Schmitt trigger, and is used to provide a DC working voltage for the two input terminals of the Schmitt trigger, so that the Schmitt trigger The DC operating voltages at the two input terminals of the flip-flop tend to be equal, and the high-pass filter is used to eliminate the DC component in the single-ended signal, and input the signal to the Schmitt trigger; The operating voltage processes the incoming single-ended signal as a differential signal.

In the circuit for converting a single-ended signal into a differential signal, the Schmitt trigger is a differential Schmitt trigger.

In the circuit for converting a single-ended signal into a differential signal, the input stage of the Schmitt trigger is a CMOS transistor or a bipolar transistor.

The circuit for converting a single-ended signal into a differential signal, wherein, when the input stage of the Schmitt trigger is a CMOS tube, the AC coupling resistance between the two input terminals of the Schmitt trigger is combined into one resistance Connected between the two input ends of the Schmitt trigger, the DC bias circuit is directly connected to any end of the resistor, the capacitor of the high-pass filter is connected to the output end of the transimpedance amplifier, and a Schmitt trigger The input end is connected to the output end of the high-pass filter, and the other input end is grounded through a voltage stabilizing capacitor.

In the circuit for converting single-ended signals into differential signals, an amplifier is added to the front end of the Schmitt trigger to improve the working range of the entire circuit.

In the circuit for converting a single-ended signal into a differential signal, the amplifier added at the front end of the Schmitt trigger is a differential amplifier.

Beneficial effects of the present invention: the present invention first uses a high-pass filter to eliminate the DC component in the signal, and then uses a differential Schmitt trigger to complete the differential conversion of the signal. The most obvious advantage of the new method is that this differential signal conversion method is applicable to both continuous mode transimpedance amplifiers and burst mode transimpedance amplifiers. That is to say, the transimpedance amplifier designed by this method can be compatible with both continuous and burst applications. In burst mode applications, this transimpedance amplifier does not require an external control signal as in the prior art.

Description of drawings

Fig. 1 is a differential conversion structure of an existing burst mode transimpedance amplifier.

Fig. 2 is a functional block diagram of the circuit provided by the present invention.

Fig. 3 is a schematic circuit diagram of the preferred embodiment 1 provided by the present invention.

Fig. 4 is a schematic circuit diagram of the preferred embodiment 2 provided by the present invention.

Fig. 5 is a circuit schematic diagram further improved on the basis of the embodiment of the present invention.

Fig. 6 is a signal waveform diagram processed by the circuit provided by the present invention.

detailed description

In order to make the object, technical solution and advantages of the present invention more clear and definite, the present invention will be further described in detail below with reference to the accompanying drawings and examples.

The differential conversion circuit for the burst mode transimpedance amplifier provided by the present invention includes a transimpedance amplifier, a high-pass filter, an AC coupling resistor, a DC bias circuit, a stabilizing capacitor and a Schmitt trigger. The Schmitt trigger is a differential Schmitt trigger, and the input stage of the Schmitt trigger can be either a CMOS or a bipolar transistor (BJT). A voltage stabilizing capacitor is connected between one input terminal of the Schmitt trigger and the ground GND. For high-frequency signals, this node is equivalent to grounding. The other input of the Schmitt trigger is connected to the output of the high-pass filter. The resistor connected between the two inputs of the Schmitt trigger is the AC coupling resistor. The output signal of the high-pass filter is applied directly between the two inputs of the differential Schmitt trigger. The DC bias circuit is connected to the AC coupling resistor and is used to provide DC working voltage for the two input ends of the Schmitt trigger. The DC bias circuit can be implemented in many ways, provided that the DC operating voltages at the two input terminals of the Schmitt trigger are close to or equal. For a differential Schmitt trigger, the input high-frequency signal is provided by a high-pass filter, and the DC operating voltage is provided by a bias circuit, so its working mode is not substantially different from that of a fully differential coupling. The circuits provided by the present invention may be implemented using typical integrated circuit technology, or may be implemented using discrete components.

The differential Schmitt trigger is a high-speed comparator with hysteresis characteristics. The output of the Schmitt trigger has two stable states: one is the output high state; the other is the output low state. Its state is maintained by the potential of the input signal, and its trigger process, that is, the input mode that causes the flip-flop to switch between two output states, also has two changes: positive trigger (potential positive increasing rising edge) and negative trigger (negative towards the decrementing falling edge). The input potential values (that is, the trigger threshold voltage) at which the two trigger processes occur are different, and are called the positive threshold voltage and the negative threshold voltage respectively.

The input voltage that changes the state of the circuit when the input signal rises from low level to high level is called the positive threshold voltage; the input that changes the state of the circuit when the input signal falls from high level to low level The voltage is called the negative-going threshold voltage. The positive threshold voltage is generally greater than the negative threshold voltage, and the difference between the positive threshold voltage and the negative threshold voltage is called voltage hysteresis.

The response of the Schmitt trigger to the three elements of positive unit width pulse, negative unit width pulse and neutral level also depends on the initial state of its output. If the initial state is a high level state, when encountering a positive unit width pulse, the output state will remain unchanged, that is, maintain its original high level state; when encountering a negative unit width pulse, the output will flip , becomes a low state. Conversely, if the initial state is a low level state, when a negative unit width pulse is encountered, the output will remain unchanged or maintain its original low level state, and the output will flip when a positive unit width pulse is encountered. becomes a high state. When the input is at mid-level, the Schmitt trigger remains in its existing state.

Referring to Fig. 3, it is a preferred embodiment one of the present invention, the signal enters the high-pass filter capacitor C2 after passing through the transimpedance amplifier at first, and directly inputs an input end of the differential Schmitt trigger from the output end of the high-pass filter, and in the Schmitt trigger A first AC coupling resistor R1 and a second AC coupling resistor R2 are connected between the two input terminals of the special trigger. A stabilizing capacitor C1 is connected between the other input terminal of the Schmitt trigger and the ground. A DC bias circuit is connected between the first AC coupling resistor R1 and the second AC coupling resistor R2. The input signal is directly loaded between the two input terminals of the Schmitt trigger, and is processed as a differential signal by the Schmitt trigger.

When the input stage of the Schmitt trigger is a CMOS tube, the present invention also provides the second preferred embodiment shown in Figure 4, since the input stage of the Schmitt trigger is a CMOS tube, the first AC coupling resistor R1 connected in series Combined with the second AC coupling resistor R2, the first resistor R is connected between the two input terminals of the Schmitt trigger, and the DC bias voltage can be added to any end of the resistor R, that is, the Schmitt trigger on any one of the inputs. One input end of the Schmitt trigger is connected to the output end of the high-pass filter, and the other input end is grounded through the voltage stabilizing capacitor C1.

Under some application conditions, the differential conversion circuit of the transimpedance amplifier can be further optimized. As shown in Figure 5, an amplifier is added to the front end of the Schmitt trigger to improve the working range of the entire circuit. This amplifier is also a differential amplifier.

To sum up all the circuits above, the present invention can be summarized as a method for converting a single-ended signal into a differential signal. The processing steps are: first use a high-pass filter to eliminate the DC component in the signal; then use a differential Schmitt trigger to Complete the differential conversion of the signal.

The high-pass filter is equivalent to a step detector in the time domain. See Figure 6, when there is a rising edge on the signal waveform diagram a, a positive pulse of unit width will appear at the rear end of the high-pass filter; conversely, when there is a falling edge on the signal waveform diagram a, there will be an AC A negative pulse of unit width appears at the rear end of the coupling resistor; while in the time period without a step, that is, the horizontal segment of the signal waveform a, the signal at the rear end of the AC coupling resistor remains unchanged at the neutral level. Therefore, the signal waveform after passing through the high-pass filter and the AC coupler becomes composed of three elements: the positive pulse of the unit width, the negative pulse of the pulse of the unit width, and the median level, as shown in b in Figure 6 shown in the waveform.

The Schmitt trigger converts the waveform composed of three elements, the positive pulse of the unit width, the negative pulse of the unit width and the median level, which is generated after the AC coupler and the high-pass filter, into an input signal with amplified amplitude. Waveform, as shown in waveform c in Figure 6.

The invention proposes a method and implementation circuit structure for converting a single-ended signal into a differential signal. This new method of differential signal conversion is to use a high-pass filter to eliminate the DC component in the signal, and then use a differential Schmitt trigger to complete the differential conversion of the signal. When applied to transimpedance amplifiers, the most obvious advantage of the invented method is that it is applicable to both continuous mode transimpedance amplifiers and burst mode transimpedance amplifiers. That is to say, the transimpedance amplifier designed by this method can be compatible with both continuous and burst applications. In burst mode applications, this transimpedance amplifier does not require an external control signal as in the prior art.

It should be understood that the application of the present invention is not limited to the above examples, and those skilled in the art can make improvements or transformations according to the above descriptions, and all these improvements and transformations should belong to the protection scope of the appended claims of the present invention.

Claims (6)

1. single-ended signal is converted to a circuit for differential signal, it is characterized in that, comprise trans-impedance amplifier, high pass filter, AC coupled resistance, direct-flow biasing circuit, electric capacity of voltage regulation and Schmidt trigger, trans-impedance amplifier connects high pass filter; High pass filter connects Schmidt trigger input; Schmidt trigger be connected electric capacity of voltage regulation between another input with ground wire; AC coupled resistance is arranged between two inputs of Schmidt trigger; Described direct-flow biasing circuit is connected between two inputs of Schmidt trigger, for providing direct-current working volts for Schmidt trigger two inputs, the direct-current working volts of Schmidt trigger two inputs are made to tend to equal, signal, for eliminating the flip-flop in single-ended signal, is inputted Schmidt trigger by described high pass filter; Described Schmidt trigger tends to equal direct-current working volts according to input and the single-ended signal of input is treated to differential signal.

2. circuit single-ended signal being converted to differential signal according to claim 1, is characterized in that, described Schmidt trigger is difference Schmidt trigger.

3. circuit single-ended signal being converted to differential signal according to claim 1, is characterized in that, the input stage of Schmidt trigger is CMOS tube or bipolar transistor.

4. circuit single-ended signal being converted to differential signal according to claim 3, it is characterized in that, when the input stage of Schmidt trigger is CMOS tube, AC coupled resistance between two inputs of Schmidt trigger is merged into the first resistance and is connected across between two inputs of Schmidt trigger, described direct-flow biasing circuit is connected directly between any one end of this first resistance, the electric capacity of high pass filter connects the output of trans-impedance amplifier, Schmidt trigger input connects the output of high pass filter, another input is by electric capacity of voltage regulation ground connection.

5. circuit single-ended signal being converted to differential signal according to claim 1, is characterized in that, increases first stage amplifier, for improving the working range of whole circuit in the front end of Schmidt trigger.

6. circuit single-ended signal being converted to differential signal according to claim 5, is characterized in that, the amplifier increased in the front end of Schmidt trigger is differential amplifier.