Method for solving crosstalk among channels of multiple audio ADC (Analog to Digital Converter)

Abstract

The invention relates to a method for solving crosstalk among channels of a multi-channel audio ADC (Analog to Digital Converter), which is realized on the basis of a signal amplitude limiting and comparison circuit of an operational amplifier, and comprises an operational amplifier U3A, an operational amplifier U3D, a diode D9, a diode D12 which are 1N4148, a capacitor C13 and a capacitor C14. According to the invention, the signal and the reference voltage are compared through the operational amplifier, the output amplitude is limited to be + / -1.65 V (reference voltage VERF) through the diode, and finally the output signal with the controlled amplitude is obtained. The signals cannot be overloaded after passing through the ADC chip, reference voltage in the ADC chip cannot be affected, and signal acquisition of other channels cannot be affected.

Description

Technical Field

[0001] This patent application belongs to the field of audio signal processing technology. More specifically, it relates to a method for solving crosstalk between multiple audio ADC channels. It can be widely used in various scenarios such as audio systems, audio amplifiers, recording equipment, and communication terminals, and is applicable to all ADC audio decoders with more than 2 channels. Background Technology

[0002] Currently available multi-channel ADCs suffer from parasitic capacitances between the source, drain, and substrate of their internal multiplexers. When the signal in one channel changes, it couples through these capacitances to the signal paths of adjacent channels, especially high-frequency signals, which are more prone to significant capacitive crosstalk due to their larger dV / dt ratios. Capacitive crosstalk is a type of intrinsic crosstalk, determined by the ADC chip's internal design and cannot be completely eliminated by external circuitry. This is unacceptable in high-end professional audio equipment. (See the related issue...) Figure 1 When a large signal is input to CH1, it is clearly visible that the input signal is transmitted to CH2 through crosstalk, causing channel 2 to also record corresponding sound. This overloads the signal on CH1, leading to instability in the chip's internal reference voltage, which in turn affects other channels.

[0003] Existing technology typically involves adding a Zener diode in front of the ADC to achieve amplitude limiting. However, this method has poor limiting performance (the amplitude cannot be limited to the specified range when the signal is very strong), which can significantly affect the audio signal and degrade the THD+N quality, which is unacceptable. Summary of the Invention

[0004] The technical problem this invention aims to solve is to provide a method for resolving crosstalk between multiple audio ADC channels. This method uses an operational amplifier to compare the signal with a reference voltage, and then uses a diode to limit the output amplitude to within ±1.65V (the reference voltage VERF), ultimately obtaining an amplitude-controlled output signal. Such a signal will not overload the ADC chip, and the internal reference voltage of the ADC chip will not be affected, thus ensuring that signal acquisition from other channels is not affected.

[0005] To solve the above problems, the technical solution adopted by the present invention is as follows: A method for resolving crosstalk between multiple audio ADC channels is based on a signal limiting and comparator circuit using operational amplifiers, comprising operational amplifiers U3A to U3D, diodes D9 to D12, capacitor C13, and capacitor C14. Operational amplifier U3A has its pin 3 connected to the reference voltage ERF + 1.65V, pin 2 connected to the input signal IN1_P, pin 4 connected to VCC + 10V, pin 1 connected to the base of diode D9, and pin 11 connected to VEE - 10V. Pin 4 of operational amplifier U3A is also connected to GND through capacitor C13, and pin 11 is also connected to GND through capacitor C14. The emitter of diode D9 is connected to the input signal IN1_P. Operational amplifier U3B has its pin 5 connected to the reference voltage ERF - 1.65V, pin 6 connected to the input signal IN1_P, and pin 7 connected to the base of diode D10. The emitter of diode D10 is connected to the input signal IN1_P. The operational amplifier U3C has its pin 10 connected to the reference voltage ERF + 1.65V, pin 9 connected to the input signal IN1_N, and pin 8 connected to the emitter of diode D11. The base of diode D11 is connected to the input signal IN1_N. Pin 12 of operational amplifier U3D is connected to the reference voltage ERF - 1.65V, pin 13 is connected to the input signal IN1_N, pin 14 is connected to the base of diode D12, and the emitter of diode D12 is connected to the input signal IN1_N.

[0006] Furthermore, operational amplifiers U3A through U3D are all TL074DR.

[0007] Furthermore, diodes D9 through D12 are all 1N4148.

[0008] Furthermore, capacitors C13 and C14 are both power supply filter capacitors.

[0009] Due to the adoption of the above technical solution, the beneficial effects achieved by this invention are: This invention limits the maximum signal between each channel by adding an audio limiting circuit to the front stage of the ADC audio decoder, preventing crosstalk without affecting the performance and specifications of all analog circuits and the ADC.

[0010] Adding this audio limiting circuit with a comparator completely solves the crosstalk problem between channels, and testing shows that all performance aspects are unaffected by the circuit. Severe crosstalk requires complex software algorithms to compensate for errors, which not only consumes CPU resources but may also have limited effectiveness due to inaccurate compensation models. Solving crosstalk simplifies the calibration process and reduces software development and maintenance costs. Furthermore, the ADC's applicability broadens, covering scenarios with higher accuracy and stability requirements.

[0011] The selected operational amplifiers U3A to U3D are all TL074DR. U3A uses dual power supplies: VCC +10V and VEE -10V. U3A, U3B, U3C, and U3D are the same chip. ABCD represents the schematic diagram of the four internal sections of the chip, so only one set of power supply labels is needed. Capacitors C13 and C14 are power supply filter capacitors, used to filter out high-frequency noise on the power lines and stabilize the power supply voltage. Attached Figure Description

[0012] Figure 1 The graph shows test data that was not used in accordance with this invention.

[0013] Figure 2 The test data diagram is for using the present invention.

[0014] Figure 3 This is the circuit schematic diagram of the present invention. Detailed Implementation

[0015] The present invention will be further described in detail below with reference to the embodiments.

[0016] One method to resolve crosstalk between multiple audio ADC channels is achieved through an audio limiting circuit located between the gain amplifier input circuit and the ADC audio decoder. The schematic diagram of the audio limiting circuit is shown below. Figure 3 .

[0017] This invention is based on a signal limiting and comparison circuit using operational amplifiers, including operational amplifiers U3A to U3D, diodes D9 to D12, capacitor C13, and capacitor C14. Operational amplifier U3A has its pin 3 connected to the reference voltage ERF + 1.65V, pin 2 connected to the input signal IN1_P, pin 4 connected to VCC + 10V, pin 1 connected to the base of diode D9, and pin 11 connected to VEE - 10V. Pin 4 of operational amplifier U3A is also connected to GND through capacitor C13, and pin 11 is also connected to GND through capacitor C14. The emitter of diode D9 is connected to the input signal IN1_P. Operational amplifier U3B has its pin 5 connected to the reference voltage ERF - 1.65V, pin 6 connected to the input signal IN1_P, and pin 7 connected to the base of diode D10. The emitter of diode D10 is connected to the input signal IN1_P. The operational amplifier U3C has its pin 10 connected to the reference voltage ERF + 1.65V, pin 9 connected to the input signal IN1_N, and pin 8 connected to the emitter of diode D11. The base of diode D11 is connected to the input signal IN1_N. Pin 12 of operational amplifier U3D is connected to the reference voltage ERF - 1.65V, pin 13 is connected to the input signal IN1_N, pin 14 is connected to the base of diode D12, and the emitter of diode D12 is connected to the input signal IN1_N.

[0018] Operational amplifiers U3A through U3D are all TL074DR. Diodes D9 through D12 are all 1N4148. Capacitors C13 and C14 are power supply filter capacitors.

[0019] As can be seen, this invention limits the maximum signal between each channel by adding an audio limiting circuit to the front stage of the ADC audio decoder, preventing crosstalk without affecting the performance and specifications of all analog circuits and the ADC. Adding this comparator limiting circuit completely solves the crosstalk problem between channels, and testing shows that all performance is unaffected by the circuit. If crosstalk is severe, complex software algorithms are needed to compensate for the error, which not only consumes CPU resources but may also have limited effectiveness due to inaccurate compensation models. Solving crosstalk simplifies the calibration process and reduces software development and maintenance costs. Furthermore, the ADC's applicability is broadened, covering scenarios with higher requirements for accuracy and stability. Figure 2 These are the test data after the problem was solved.

[0020] This circuit mainly consists of an operational amplifier TL074DR, a diode 1N4148, and a filter capacitor. It can be viewed as a signal limiting and comparison circuit based on an operational amplifier, and its working principle is as follows: 1. The working principle of operational amplifiers The TL074DR is a four-channel JFET input operational amplifier characterized by high input impedance and low noise. The circuit provides dual power supplies for the operational amplifier: VCC +10V and VEE -10V, ensuring its operation over a wide voltage range. Capacitors C13 and C14 are power supply filter capacitors used to filter out high-frequency noise on the power lines and stabilize the power supply voltage.

[0021] 2. In-phase comparison and amplification logic Operational amplifiers U3A and U3C: Their non-inverting inputs (pin 3 of U3A and pin 10 of U3C) are connected to the reference voltage ERF + 1.65V. Input signals IN1_P and IN1_N are directly connected to the inverting inputs of the operational amplifiers (pin 2 of U3A and pin 9 of U3C). Based on the operational amplifier's characteristic that "the voltage at the non-inverting input determines the output trend," when the input signal voltage is lower than ERF + 1.65V, the operational amplifier will output a high level close to VCC + 10V; when the input signal voltage is higher than ERF + 1.65V, the operational amplifier will output a low level VEE - 10V.

[0022] Operational amplifiers U3B and U3D: Their non-inverting inputs, pin 5 of U3B and pin 12 of U3D, are connected to the reference voltage ERF -1.65V. Input signals IN1_P and IN1_N are also directly connected to the inverting inputs of the operational amplifiers, pin 6 of U3B and pin 13 of U3D. Similarly, when the input signal voltage is higher than ERF -1.65V, the operational amplifier outputs a high level; when the input signal voltage is lower than ERF -1.65V, the operational amplifier outputs a low level.

[0023] 3. Limiting effect of diodes The diodes D9 / D10 / D11 / D12 in the circuit are ordinary switching diodes with a forward voltage drop of about 0.7V, and their model number is 1N4148 (1N4148 SOD123).

[0024] When the operational amplifier outputs a high level, if the voltage exceeds the forward voltage drop of the corresponding diode, the corresponding diode will conduct, clamping the output voltage to near the "reference voltage + diode forward voltage drop"; When the operational amplifier outputs a low level, if the voltage is lower than the "ground potential - diode forward voltage drop", the corresponding diode will be reverse cut off (or forward conduction, depending on the current direction), further constraining the range of the output voltage.

[0025] 4. Overall signal flow The input differential signals IN1_P and IN1_N enter the upper and lower branches, respectively, which consist of operational amplifiers and diodes. The upper branch (U3A, U3B, D9, D10) processes the IN1_P signal, and the lower branch (U3C, U3D, D11, D12) processes the IN1_N signal. Through comparison with the reference voltage by the operational amplifier and limiting by the diodes, signals constrained within a specific amplitude range are finally output from OUT1_P and OUT1_N, which can be used in subsequent circuits with strict signal amplitude requirements.

[0026] 5. Reference power supply requirements For an ADC chip with a full-amplitude voltage of 3.3Vrms corresponding to 0dBFS, a reference voltage of ±1.65V is selected. ADC chips with other parameters can use appropriate reference voltages. Furthermore, the temperature drift, error, and noise of the reference voltage will affect the limiting effect and audio signal specifications. In actual product manufacturing, the reference voltage value needs to be fine-tuned to correct for errors in the chip manufacturing process and the limiting diode manufacturing process.

[0027] Figure 1 The graph shows test data not using this invention. It can be seen that the red line clearly has a peak. Blue represents CH1, with a value of +1.870 dBFS. Red represents CH2, with a value of -23.377 dBFS. Figure 1 The +1.870dBFS value refers to the digital signal at the input of channel 1, while the maximum value for the digital input is 0dBFS. This indicates that the signal input to channel 1 is a very strong overload signal. The value -23.377dBFS refers to the signal at the input of channel 2, which is -23.377dBFS. However, during the test, only channel 1 had a signal input, while channel 2 had no input signal. Therefore, it can be determined that -23.377dBFS indicates crosstalk between channel 1 and channel 2 within the ADC decoding chip. A large input signal from channel 1 can easily crosstalk to channel 2, causing channel 2 to hear the same input sound as channel 1 even when no signal is inserted.

[0028] Figure 2 The test data graph used in this invention shows that the red line is a straight line, and the peaks or bumps no longer exist. Blue represents CH1, with a value of +1.875 dBFS. Red represents CH2, with a value of -110.746 dBFS. Similarly, Figure 2 The +1.870dBFS value refers to the digital signal at the input of channel 1, while the maximum value at the digital input is 0dBFS. This indicates that the signal input to channel 1 is a very strong overload signal. The -110.746dBFS value for channel 2 refers to the value obtained after testing through this limiting circuit. The signal at the input of channel 2 is -110.746dBFS, thus proving that this limiting circuit can perfectly solve the crosstalk problem between channel 1 and channel 2 within the ADC decoding chip.

Claims

1. A method for resolving crosstalk between multiple audio ADC channels, characterized in that: This is implemented using a signal limiting and comparator circuit based on operational amplifiers, including operational amplifiers U3A to U3D, diodes D9 to D12, capacitor C13, and capacitor C14. Operational amplifier U3A has its pin 3 connected to the reference voltage ERF + 1.65V, pin 2 connected to the input signal IN1_P, pin 4 connected to VCC + 10V, pin 1 connected to the base of diode D9, and pin 11 connected to VEE - 10V. Pin 4 of operational amplifier U3A is also connected to GND through capacitor C13, and pin 11 is also connected to GND through capacitor C14. The emitter of diode D9 is connected to the input signal IN1_P. Operational amplifier U3B has its pin 5 connected to the reference voltage ERF - 1.65V, pin 6 connected to the input signal IN1_P, and pin 7 connected to the base of diode D10. The emitter of diode D10 is connected to the input signal IN1_P. The operational amplifier U3C has its pin 10 connected to the reference voltage ERF + 1.65V, pin 9 connected to the input signal IN1_N, and pin 8 connected to the emitter of diode D11. The base of diode D11 is connected to the input signal IN1_N. Pin 12 of operational amplifier U3D is connected to the reference voltage ERF - 1.65V, pin 13 is connected to the input signal IN1_N, pin 14 is connected to the base of diode D12, and the emitter of diode D12 is connected to the input signal IN1_N.

2. The method for solving crosstalk between multiple audio ADC channels according to claim 1, characterized in that: Operational amplifiers U3A through U3D are all TL074DR.

3. The method for solving crosstalk between multiple audio ADC channels according to claim 1, characterized in that: Diodes D9 through D12 are all 1N4148.

4. The method for solving crosstalk between multiple audio ADC channels according to claim 1, characterized in that: Capacitors C13 and C14 are both power supply filter capacitors.

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