TWI222270B - On-chip high-pass filter with large time constant - Google Patents

Abstract

An on-chip high-pass filter with large time constant comprising a capacitor, a first transistor having a first terminal connected to a first voltage source and a second terminal connected to the capacitor, and a second transistor having a first terminal connected to the second terminal of the first transistor and a second terminal connected to ground, wherein the first transistor and the second transistor are for operating as a large-resistance resistor. The electrical equivalent large-resistance resistor and the capacitor together form a high-pass filter between the input port and the output port.

Description

1222270 V. Description of the invention (1) Technical field to which the invention belongs The present invention provides a high-pass filter, especially a high-pass filter with a large time constant. Prior art In order to filter the DC portion of the signal or reduce the DC offset (DC 0 f f s e t), many circuits require the use of high-pass filters. Circuits like DC voltage blocking capacitor, DC voltage level shifter, and DC servo loop are all designed to implement the function of a high-pass filter. In a circuit using two voltage sources with different DC levels, it is not possible to directly connect a signal from one power supply domain to another. In order to connect signals in two power domains, a DC level converter can be used to convert the DC level of the first power domain to the DC level of the second power domain. However, with the improvement of the integrated circuit and device manufacturing process, the operating voltage on the chip has been greatly reduced, and it is actually low enough to meet the operation requirements of the DC level converter. In this case, a high-pass filter can be used to block the DC signal and filter the desired signal. If the corner frequency of the high tear wave device is low enough, using a high pass tear wave device will not have an adverse effect on the system. ° ^

1222270 V. Description of the invention (2) 'DC offset voltage' is not available in zero intermediate frequency receivers, mixers and low pass filters (low pass fi 1 ters) Neglected points. If not removed, unwanted dc offsets can cause sensitive devices such as analog-to-digital converters (ADC converters) to fail due to oversaturation. The general solution to this problem is to add a DC servo loop. The DC servo loop uses feedback to keep the DC level stable. However, the smaller the feedback window (meaning the angular frequency is very low), the longer the stabilization time (s e 111 i ng t i m e) will be. When the angular frequency is low, not only the resistance value of the resistor in the filter and the capacitance of the capacitor are large, but also the stabilization time is usually too long. Using a simple high-pass filter, not only can achieve the same function as the DC servo return, but there is no problem that the closed loop stabilization time is too long. Question 1 Figure 1 shows a conventional high-pass filter. A capacitor 丨 2 is connected to an input port 14 and an output port 16, and a resistor i 8 is connected to the output port j 6 and ground. When using a standard resistor / capacitor high-pass filter i0 as shown in Figure 1, a resistor with two impedances 18 and a capacitor with high capacitance must be used to generate the ideal low angular frequency. If the angular frequency energy is to be as low as 100 Hz (or ~ 2 times), the resistance value of the resistor 18 must be millions of ohms (Mohm) and the capacitance of the capacitor 12 will reach hundreds of picofarads (pF). Range. For example, if the desired angular frequency (Fc) is 100Hz, the formula Fc = 1/1

Page 7 1222270 V. Description of the invention (3) (2ττ R * C) It can be seen that the capacitance of the capacitor 12 is 50pF, and the impedance of the resistor 18 must be as high as 33Mohm. Such large values of impedance and capacitance require a very large IC area. In fact, the IC area required for the high-pass filter 10 may be several times that of other design parts. Rong Neiming has a wide range of timings and low frequency angles. The eye-catcher's clear and high-frequency data of the main filter is often due to the general preparation of the crystal • IL | Species one by one revealed first, the system, the electric range: Li Hanzhuan Please include, the number of the application of the application of the device of the Ming-Fu Ming-duo to the second end of the first two •, the second terminal of the first and second terminal connected to the second terminal and the second terminal of the first and second to the source The crimping electrical terminal 1 is connected to the crystal terminal reactance and common resistance, and the large terminal is an output group and the input terminal is the input body. Body reactor Crystal resistance wave Electric Dadu Yixiaotong High school should be one of them. The resistance and ground power are the same as the embodiment. Please refer to FIG. 2 for a schematic diagram of the high-pass filter 20 of the present invention. The high-pass filter 20 includes an input port 22, an output port 24, a capacitor 26, a p-type transistor 28, an n-type transistor 30, and a voltage source 32. Capacitor 26 is connected between input port 2 2 and output port 2 4. Source of p-type transistor 2 8

1222270 V. Description of the invention (4) Electrode body 28 connected to a voltage transistor 3 0 and n-type transistor bone voltage source 32 are mainly electrodeless (L) and width of the transistor operating in mode (Operation, the drain current I j is fixed. However, there is a slight change between the drain and the source. The electricity is at the drain-source voltage ^ Off. VDS = 1 / "If the transistor is at full impedance from the drain The current I can be regarded as an equivalent electric current 2 2 and the output port 24. The magnitude of the current I ranges from uA to 100 μm. Therefore, a chip supply VDDa drain can be easily connected to the output Port 24. The n-type is connected to the output bee 24 and the source is grounded. The gates of the p-type transistor 3 0 are connected to the output of the voltage source 32. Both p-type transistors and n-type transistors are provided. It can be at a full potential. The current size is calculated according to the channel length determined in the process.) When the transistor is operated in the saturation mode, the size is maintained in the actual circuit due to the channel length modulation effect. The voltage VD will change and the output impedance R of the drain current crystal is l / (ID *; l), where the parameter input! Is in the saturation region and is in linear phase with the drain current. I is the early voltage. Therefore, the mode operation can be regarded as an equivalent resistance. Decided. Therefore, the ρ-type transistor and the n-type transistor both resist, and the equivalent resistance and the capacitor 26 together form a high-pass wave wave between the input 。. Usually between 0 · 01 to 0 · 03 V-1 And the drain electrode m Α. In this method, the output impedance r 〇 can reach the way that the digital transistor operates as a large impedance resistor, with a high-pass filter with a large time constant 1222270 V. Description of the invention (5) Please Note two, of course, the detailed description of the above preferred embodiment uses a Mos transistor, but it is just an example, and the present invention is also applicable to a BJT transistor. &Amp; Output of transistor 28 and n-type transistor 3 The impedance value of the impedance is very sensitive to the gate potential provided by the voltage source 32. In theory, if there is no process error in the process of the integrated circuit (pr0cess van at ion ', that is, the parameter difference caused by the process error ), The electric dust source 3 2 will produce the same The voltage signal will have the same output impedance impedance as the? -Type transistor 28 and the n-type transistor 30. The angular frequency of the related high-pass filter 2 will be the same for all integrated circuits. In practice, 'the parameter values of the transistor will be slightly different due to process differences', so these variations must be considered to determine that in different integrated circuit processes, the p-type transistor 28 and the n-type transistor The equivalent impedance of 30 is the same as that of the impedance. The schematic diagram of a high-pass filter 40 with a bias replica voltage generator 42 is shown in FIG. 3. The bias replication voltage source 42 includes a p-type transistor 44 that is substantially the same size as the p-type transistor & and an n-type transistor 4 that is substantially the same size as the n-type transistor 3 0 6. The source of the p-type transistor 44 is connected to a voltage source V D D and its terminal is connected to a voltage source node A. The drain of the n-type transistor 46 is connected to the voltage source node A and its source is grounded. The gates of both the p-type transistor 4 4 and the n-type transistor 4 6 are connected to 1222270 V. Description of the invention (6) To the voltage source node A. Since the size and design of the P-type transistor 44 and the n-type transistor 46 are the same as those of the p-type transistor 28 and the n-type transistor 30 in the high-pass filter 40, the voltage source of the voltage source 42 is copied by the deviation The level signal generated by the node A can be used to represent process differences in different integrated circuit processes. By adjusting the length and width of the transistor channels of the p-type transistor 28 and the n-type transistor 30, and selecting a capacitor 26 of an appropriate size, the angular frequency and time constant formed by the high-pass filter can be directly controlled. The offset replication voltage source 42 ensures that the same angular frequency response can be achieved regardless of process differences. Please refer to FIG. 48 for the frequency response of the high-pass filter 40 proposed by the present invention shown in FIG. As shown in Figure 4, ρ-type transistors 28 and 44 with a channel width of W = m and a length of L = 2 0 // m are selected; η-type transistors with a channel width of W = 1 // m and a length of L = 2 0 / zm Crystals 30 and 46; and the capacitance C of the capacitor 26 is selected to be 13 pF, the angular frequency (Fc) obtained by the high-pass filter will be equal to 100 Hz. Such a high-pass filter 40 is easier to implement on integrated circuits and more economical in design space compared to conventional techniques. Please refer to FIG. 5, which shows a schematic diagram of a high-pass filter 50 with a variable bias replica voltage generator 52. The variable bias replication voltage source 5 2 includes a p-type transistor 54 that is substantially the same as a p-type transistor 2 8 and a p-type transistor 54 that is substantially the same as a p-type transistor.

Page 11 1222270 V. Description of the invention (7) ^ ----- = 3 0-type n-type transistor 5 6 and an amplifier having a non-inverting input, an inverting input and an output 58. The source of ^ is connected to the voltage source VDD and its drain is connected to the amplifier 58 = = input. The drain of the n-type transistor 56 is connected to the non-inverting input terminal of the amplifier 58 and its source is grounded. The gates of both the P-type transistor 54 and the n-type transistor 56 are connected to a voltage source node A. A quasi-signal Vb? As is connected to the inverting input terminal of the amplifier 58 and the output terminal of the amplifier 58 is connected to the voltage source node A. Similar to the bias replication voltage source 4 2 shown in Fig. 3, because the p-type transistor 5 4 considers the size and design of the n-type transistor 5 6 and local filtering, wave | ρ-type transistor 2 in § 5 2 The 8 and n-type transistors 30 are the same, so the level signal generated by the voltage source node A of the variable bias replica voltage source 52 can be targeted at the process difference in the integrated circuit manufacturing process. By adjusting the length and width of the transistor channels of the p-type transistor 28 and the n-type transistor 3 0, and selecting a proper size of each 2 6 ′, the angular frequency and Time hanging number. Selected p-type transistors 28 and 54 with channel width W = 2 / zm and length L = 20 // m; n-type transistors 30 and 56 with channel width W = l // m and length L = 20 // m; And select the capacitance of the capacitor 26 6 = 13 mouth? The resulting angular frequency (F c) is equal to 100 〇 ζ and the same frequency response as shown in Figure 4 will be obtained. An additional advantage of this variable bias replica voltage source is that the level shift of the output port 24 of the high-pass filter 50 will track the level signal Vb i as input to the inverting wheel input 60 of the amplifier 58. . The variable bias replica voltage source 52 can directly control the DC offset of the high-pass filter 50. Level signal Vb i as can be connected

1222270 V. Description of the invention (8) The acceptance range is as follows: ¥ 1: < 乂 1) 133 < (丫 00- ¥ 1 :). The voltage gain of the amplifier 58 should be high enough to provide the desired accuracy of the output DC of f set error. The higher the voltage gain of the amplifier 58, the lower the DC offset error of the output port 24 of the high-pass filter 50 appears. See Figure 6 for the intention of a differential Nantong crossing ^ § 70. This differential implementation is usually used in high-speed integrated circuit environments and has much higher common mode noise rejection capabilities. The differential Nantong crossing wave device 70 includes a forward input port 72, a forward output port 74, a forward capacitor 76, a forward p-type transistor 78, a forward p-type transistor 80, and a negative input. Port 82, a negative output port 84, a negative capacitor 86 that is the same as the positive capacitor 76, a negative p-type transistor 8 8 that is the same as the positive P-type transistor 78, and a positive n-type Transistor 80 is the same negative-type n-type transistor 90, and a bias replication voltage source 42 is used. The bias is the same between 7 4 and 8 4. The poles are connected to the positive and are connected to the transistor. The components and operating modes of the positive and negative voltage replication voltage source 42 are the same as those in Figure 3. The forward power valley 7 6 is connected to the forward input port 7 2 and the forward output port. A negative capacitor 86 is connected to the negative input port § 2 and the negative output port. The source of the forward p-type transistor 78 is connected to the power supply VDD and it is drawn to the forward output port 74, and the drain of the forward n-type transistor 80 is connected to the output port 74 and its source is grounded. The source of the negative p-type transistor 88 is VDD and its drain is connected to the negative output port 84, and the drain of the negative n body 90 is connected to the negative output port 84 and its source is grounded. Xiangcheng is connected to the gates of n-type transistors 7 8, 8 0, 8 8, 9 0

Page 13 1222270 V. Description of the invention (9) To the voltage source node A, which is connected to the output terminal of the bias copy voltage source 42. The operation of the differential high-pass filter 70 is very similar to the single-end version shown in FIG. 3, but the difference is that in FIG. 6, the forward high-pass filter is copied to produce A negative high-pass filter required for differential operation. The positive and negative operating modes of this circuit are the same as the high-pass filter shown in Figure 3. Please refer to FIG. 7 for a schematic diagram of another differential high-pass filter 100. The differential high-pass filter 100 can be used when the DC offset of the positive and negative output ports 74, 84 needs to be controlled. The schematic diagram of this circuit is very similar to the differential high-pass filter 70 shown in Fig. 6 except that the level signal of the voltage source node A is generated by the variable bias replica voltage source 52. The positive and negative high-pass filters of this circuit operate in the same way as the components shown in Figure 6. The components and operation modes of the variable bias replication voltage source 52 are the same as those shown in FIG. Compared with the conventional technology, the present invention uses a p-type transistor and an n-type transistor to form a predetermined impedance value, so that a high-pass filter can be implemented on the integrated circuit. The predetermined impedance value and a capacitor together form a high-pass filter between the input port and the output port, so that it can be achieved without adding resistance and capacitance values to the integrated circuit. The present invention obtains a predictable impedance value by a combination of a bias replication voltage source, a p-type and an n-type transistor. The present invention reproduces voltage by using a variable bias

Page 14 1222270 V. Description of the invention (10) The source can directly control the DC offset of the output port of the high-pass filter. In addition, it can also maintain a predictable impedance value regardless of the program variation when the integrated circuit is manufactured. The above description is only a preferred embodiment of the present invention, and all equivalent changes and modifications made in accordance with the scope of the patent application for the present invention shall fall within the scope of the patent of the present invention. End of chapter

Page 15 1222270 Brief description of the diagram Brief description of the diagram Figure 1 is a schematic diagram of a high-pass filter in the conventional technology. FIG. 2 is a schematic diagram of a high-pass filter according to the present invention. Figure 3 is a schematic diagram of the high-pass filter in Figure 2 equipped with a biased replica voltage source. Figure 4 shows the frequency response of the high-pass filter in Figure 3. FIG. 5 is a schematic diagram of the high-pass filter in FIG. 2 provided with a variable bias replicating voltage source. FIG. 6 is a schematic diagram of a differential type of the high-pass filter in FIG. 3. FIG. 7 is a schematic diagram of a differential type of the high-pass filter in FIG. 5. Schematic symbol description

Page 16 10, 20 > 40, 50 ~ 70 > 100-pass filter 48 Frequency response graph 12 ^ 26 '76 > 86 capacitor 14, 22 > Ί2, 82 input port 16 > 24, 74' 84 output port 18 resistance 28 , 44-54 '78 ~ 88 P-type transistor 30, 46 > 56' 80 > 90 N-type transistor 32 Voltage source 42 Bias voltage source 1222270 Brief description of the diagram 52 Variable bias voltage source 5 8 Amplifier 60 Inverting input of amplifier 5 8 IHI1 Page 17

Claims (1)

1222270 6. Scope of patent application 1. A high-pass filter comprising: a capacitor; a first transistor having a first terminal connected to a first voltage source and a second terminal connected to the capacitor; and a second capacitor The first end of the crystal is connected to the second end of the first transistor, and the second end of the crystal is grounded. The time constant of the high-pass filter is determined by the first transistor and the second transistor. 2. The high-pass filter according to item 1 of the scope of patent application, wherein the first transistor is an n-type transistor. 3. The high-pass filter according to item 1 of the patent application scope, wherein the second transistor is a P-type transistor. 4. The high-pass filter according to item 1 of the patent application scope, further comprising a second voltage source connected to the third terminals of the first and second transistors, so that the first and second transistors can Operates in a saturated mode. 5. The high-pass filter according to item 4 of the scope of patent application, wherein the second voltage source includes: a third transistor, a first terminal of which is connected to the first voltage source, and a second terminal of which is connected to the The third terminal of the first and the second transistor, the third terminal of which is connected Page 18 1222270 6. The scope of the patent application is to its second end; and a fourth transistor whose first end is connected to the second end of the first transistor, whose second end is grounded, and whose third end is connected to Its first end. 6. The high-pass filter according to item 4 of the scope of patent application, wherein the second voltage source includes: a third transistor including a first terminal, a second terminal, and a third terminal, One terminal is connected to the first voltage source. A fourth transistor includes a first terminal, a second terminal, and a third terminal. The first terminal is connected to the second terminal of the first transistor. The second terminal is grounded; and an amplifier whose first input terminal is connected to the second terminal of the first transistor, its second input terminal is connected to a bias source, and its output terminal is connected to the first, second, The third terminal of the third and fourth transistors. 7. The high-pass filter according to item 1 of the patent application scope, wherein the high-pass filter is built in a chip. 8. The high-pass filter according to item 1 of the patent application, wherein the first and second transistors are capable of operating in a saturation mode. Page 19