RU2517698C1 - Broadband attenuator for high-speed analogue and analogue-digital interfaces - Google Patents

Abstract

FIELD: radio engineering, communication.

SUBSTANCE: broadband attenuator for high-speed analogue and analogue-digital interfaces comprises a first resistor (3), an input voltage source (4) connected via alternating current between a common bus (5) and the input of the device (1), a second resistor (6) connected via alternating current between the output of the device (2) and the common bus (5), equivalent capacitance of a load (7), connected via alternating current between the output of the device (2) and the common bus (5), a non-inverting voltage follower (8), a non-inverting current follower (10), and the two-terminal element of a correction circuit (11) is connected between the output of the non-inverting voltage follower (8) and the input of the non-inverting current follower (10).

EFFECT: wider operating frequency range of the device and faster operation thereof when working with high-amplitude pulsed signals.

2 cl, 7 dwg

Description

The present invention relates to the field of measurement technology, electrical engineering, radio engineering, communications and can be used in the structure of various interfaces, measuring instruments, high-speed analog-to-digital (ADC) and digital-to-analog (DAC) converters.

The device information and measuring equipment, communications, automation and radio are widely used resistive voltage dividers - attenuator (AT), providing a predetermined division (weakening) of the input voltage (u _Rin) [1-16]. With an increase in the frequency u _in in such attenuators, significant signal transmission errors arise due to the influence of the parasitic capacitor Co of the load circuit, which is formed, for example, in the parallel ADC by the input capacitance of the comparator. The reduction of these errors is one of the problems of modern information-measuring equipment, which is solved today both due to the AT circuitry and due to the design features of the input circuits (for example, special “probes” of microwave voltmeters, oscilloscopes, antenna systems for radio receivers, etc. .).

Due to the widespread use of resistive attenuators in various fields of technology, they are present in various classes (IPC H03H 7/24, A61B, G01R 31/02, H01P 1/22, H03K 5/08, H03L 5/00, G01R 27/00 , G05F 3/00, H01H 47/00, H03G 3/20).

The proposed circuit solution relates to a subclass of attenuators in which the transmission coefficient can vary widely due to changes in the resistances of the resistors forming its structure. Such tasks are typical in the design of digital-controlled attenuators [patents US 4.837.530, US 4.839.611 fig.2, US 7.477.085, EP 2.337.219 fig. 2] and parallel ADC [patents US 8.076.995 fig. 1,2, 7.394.420 fig. 2, 7.253.700 fig. 1, 5.231.399 fig. 2, 6.437.724, patent applications US 2007/0176664 fig. 5, 2008/0036536 fig. 43, US patents 5.307.067 fig.3, 7.248.192 fig.5].

The closest prototype of the claimed device is the resistive voltage divider of figure 1, presented in patent application US 2012/0086528 fig. 8 V. It has an input 1 and an output 2 of the device, between which the first resistor 3 is connected, the input voltage source 4 is turned on by alternating current between the common bus 5 and the input of the device 1, the second resistor 6 is turned on by alternating current between the output of the device 2 and a common bus 5, the equivalent load capacity 7, connected by alternating current between the output of the device 2 and the common bus 5.

A significant disadvantage of the attenuator prototype of figure 1 is that with increasing frequency of the input signal, its transmission coefficient decreases significantly due to the shunt effect of the equivalent load capacitance 7. This limits the frequency range of the attenuator and, as a result, the speed, for example, parallel ADCs. Even more significant frequency errors in the prototype attenuator arise with a large change in the resistances of its first 3 and second 6 resistors, which in practice is carried out using instead of a resistor 6 a gate-controlled field-effect transistor or digital-controlled impedances.

The main objective of the invention is to significantly expand the range of operating frequencies of the device and increase its speed when working with pulsed signals of large amplitude. Moreover, the achievement of these quality indicators is ensured in a wide range of variation of the transmission coefficients AT (K ₀ ), which is determined by the ratio K ₀ = R ₆ / (R ₆ + R ₃ ). This is one of the remarkable features of the proposed device, which expands the scope of its application, for example, in broadband digital-controlled attenuators, R-2R voltage dividers of high-speed analog-to-digital converters, etc.

This object is achieved in that in the attenuator of Fig. 1, containing the input 1 and output 2 of the device, between which the first resistor 3 is connected, the input voltage source 4 is turned on by alternating current between the common bus 5 and the input of the device 1, the second resistor 6 is turned on for alternating current between the output of device 2 and the common bus 5, the equivalent load capacitance 7, included for alternating current between the output of the device 2 and the common bus 5, new elements and connections are provided - the output of the device 2 is connected via alternating current to the input of non-in tiruyuschego voltage follower 8 and 9 non-inverting current output of current mirror 10, and between the output of non-inverting voltage follower 8 and the noninverting input of the repeater 10 is turned on current bipole correction circuit 11.

Figure 1 shows a diagram of an attenuator prototype.

Figure 2 presents a diagram of the inventive device in accordance with claim 1 and 2 of the claims.

Figure 3 shows the frequency dependence of the transfer coefficient of the attenuator of Figure 2 on the capacitance of the capacitor 12 (C ₁₂ = C _k ) at R ₃ = 10 kOhm, R ₆ = 1 kOhm, i.e. at K ₀ ≈0.1. These, as well as subsequent graphs, were obtained as a result of modeling the circuit of FIG. 2 in the Cadence environment on models of integrated components.

Figure 4 shows the frequency dependence of the transfer coefficient of the attenuator of Figure 2 on the capacitance of the capacitor 12 (C ₁₂ = C _k ) at R ₃ = R ₆ = 1 kOhm, i.e. at K ₀ = 5.

Figure 5 shows the frequency dependence of the transfer coefficient of the attenuator of Figure 2 on the capacitance of the capacitor 12 (C ₁₂ = C _k ) at R3 = 1 kOhm, R ₆ = 100 Ohm, i.e. when K ₀ = R ₆ / (R ₆ + R ₃ ) = 0.09.

Figure 6 shows the frequency dependence of the transfer coefficient of the attenuator of figure 2 with R ₆ = 1 kΩ, C ₁₂ = C _k = l, 9 pF and various values of the resistance of the resistor R3 (1 kΩ, 5 kΩ, 10 kΩ). The given values of the elements correspond to K ₀ = 0.5; 0.166; 0.09.

Figure 7 shows the frequency dependence of the transfer coefficient of the attenuator of figure 2 at R ₆ = 1 kOhm, C ₁₂ = C _k = 2 pF and various values of the resistance of the resistor R3 (1 kOhm, 5 kOhm, 10 kOhm). In this ideal case, with an output of C ₁₂ = C _k = 2 pF, the maximum possible extension of the frequency range AT is ensured independently of K ₀ .

The broadband attenuator of FIG. 2 comprises an input 1 and an output 2 of the device, between which a first resistor 3 is connected, an input voltage source 4 connected by alternating current between the common bus 5 and the input of the device 1, and a second resistor 6 connected by alternating current between the output of the device 2 and common bus 5, equivalent load capacitance 7 connected by alternating current between the output of device 2 and common bus 5. The output of device 2 is connected by alternating current with the input of the non-inverting voltage follower 8 and the current output 9 non-inverting second current repeater 10, and between the output of non-inverting voltage follower 8 and the noninverting input of the repeater 10 is turned on current bipole correction circuit 11.

In Fig.2, in accordance with claim 2 of the claims, the two-terminal correction circuit is made in the form of a capacitor 12, the capacitance of which is functionally related to the equivalent load capacitance 7.

Consider the operation of the device of figure 2.

передается в цепь нагрузки на выход 2:When the voltage transfer coefficient (K _y ) of the non-inverting voltage follower 8 K _y = 0 and the current transfer coefficient (K _i ) of the non-inverting current follower 10 K _i1 = 0 input voltage change $${\dot{U}}_{\mathrm{at}x}$$

transferred to the load circuit on output 2:

$${\dot{U}}_{\mathrm{at}sx.}\approx \frac{{\mathrm{TO}}_0}{\mathrm{one}+j\omega {\tau }_n}{\dot{U}}_{\mathrm{at}x},(\mathrm{one})$$

where τ _n = R _3.6 C ₇ ,

R _3.6 = R ₃ R ₆ / (R ₃ + R ₆ ).

- коэффициент передачи AT в диапазоне низких частот. $${\mathrm{TO}}_0=\frac{U_{\mathrm{at}sx}}{U_{\mathrm{at}h}}=\frac{R_6}{{\mathrm{<figure-callout\; id="6"\; label="R"\; filenames="00000014.png"\; state="\{\{state\}\}">R</figure-callout>}}_6+R_3}$$

- AT transmission coefficient in the low frequency range.

поступает на выход неинвертирующего повторителя напряжения 8 с низким выходным сопротивлением, что создает входной (İ₁₁), а затем выходной (İ₉) токи неинвертирующего повторителя тока 10, который в идеальном случае имеет нулевое входное сопротивление:In the circuit of figure 2, when K _y ≠ 0, K ₁ ≠ 0, the output voltage of the device $${\dot{U}}_{\mathrm{at}sx}$$

goes to the output of the non-inverting voltage follower 8 with a low output resistance, which creates the input (İ ₁₁ ) and then output (İ ₉ ) currents of the non-inverting current follower 10, which ideally has zero input resistance:

$${\dot{I}}_{\mathrm{eleven}}=\frac{{\dot{U}}_{\mathrm{at}sx}{\dot{K}}_{\mathrm{at}}}{\mathrm{one}/j\omega C_{12}},(\mathrm{fourteen})$$

$${\dot{I}}_9=j{\dot{K}}_i{\dot{K}}_{\mathrm{at}}\omega C_{12},(\mathrm{fourteen})$$

- комплекс коэффициента передачи по току неинвертирующего повторителя тока 10;Where $${\dot{K}}_i$$

- complex current transfer coefficient of a non-inverting current follower 10;

- комплекс коэффициента передачи по напряжению неинвертирующего повторителя напряжения 8. $${\dot{K}}_y$$

- complex transmission coefficient for voltage non-inverting voltage follower 8.

) и выходного ( $${\dot{U}}_{вых}$$

) напряжений схемы фиг.2 можно записать следующее уравнение In linear mode for input complexes ( $${\dot{U}}_{\mathrm{at}x}$$

) and output ( $${\dot{U}}_{\mathrm{at}sx}$$

) of the voltage circuit of figure 2, you can write the following equation

$${\dot{U}}_{\mathrm{at}sx}={\dot{U}}_{\mathrm{at}x}\frac{{\mathrm{TO}}_0}{\mathrm{one}+j\omega {\tau }_{3.6}\left(\mathrm{one}-{\dot{K}}_{\mathrm{at}}{\dot{K}}_i\frac{C_{12}}{C_7}\right)},(\mathrm{one})$$

, $${\dot{K}}_i=1$$

, то, как следует из (2), условием существенного уменьшения влияния эквивалентной емкости нагрузки C7 на амплитудно-частотную характеристику аттенюатора фиг.2 будет равенствоIf you provide $${\dot{K}}_y=\mathrm{one}$$

, $${\dot{K}}_i=\mathrm{one}$$

, then, as follows from (2), the condition for a significant reduction in the effect of the equivalent load capacitance C7 on the amplitude-frequency characteristic of the attenuator of FIG. 2 is the equality

$$\frac{C_{12}}{C_7}{K}_{\mathrm{at}}{K}_i=\mathrm{one}(3)$$

In this ideal case, the factor at τ _3.6 in (2) is zero and, as a result, the gain of the attenuator becomes frequency-independent. These findings are confirmed by modeling.

Therefore, in a first approximation, when K _y = K _i = 1, the capacitances of the capacitors C ₁₂ and C ₇ should have the following relationship: C ₁₂ ≤C ₇ .

Thus, in the scheme of figure 2, conditions are created for a significant expansion of the low-signal range of operating frequencies, which in practice will be determined (or limited) by the inertia of the non-inverting current follower 10 and the non-inverting voltage follower 8.

In the event that the equivalent load capacitance 7 is not an ideal capacitor and contains, for example, a parasitic resistor connected in series with the capacitance, then the two-terminal circuit of the correction circuit 11 should contain similar elements.

From the graphs of figure 5, in particular, it follows that the range of operating frequencies of the proposed attenuator (at C ₇ = 2 pF, C ₁₂ -C _to = 1.9 pF and ideal current follower 10 and voltage follower 8) is expanded to 2 GHz, while the upper cutoff frequency of the classical attenuator (at -3dB level) has a value of 100 MHz.

The graphs of Fig.6 show that when the resistance of the resistor 3 (R3) is changed 10 times, the upper cutoff frequency of the transmission coefficient of the inventive attenuator is practically unchanged.

The analysis performed above, as well as the results of computer simulations show that in the circuit of figure 2 one of the problems of modern analog microcircuitry is solved - expanding the frequency range and increasing the speed of signal attenuators, which are the basic unit of analog and analog-to-digital converters.

Bibliographic list.

1. Patent US 5.867.018.

2. US Pat. No. 5,363,070, fig. 2a.

3. Patent US 4.912.394.

4. Patent US 8.076.995.

5. Patent US 4.050.055, fig. 5.

6. US Pat. No. 4,198,988, fig. one.

7. Patent application US 2007/0176664, fig. 2.

8. Patent US 4.839.611, fig. 2.

9. Patent US 4,670,723, fig. 2.

10. Patent US 4,272,739, fig. one.

11. JP patent 10-211-0068595.

12. JP patent 2010-252241.

13. Patent EP 2337219, fig. 2.

14. Patent EP 0753937, fig. one.

15.Patent EP 0612982.

16. Patent US 7.477.085, fig. one.

Claims (2)

1. A broadband attenuator for high-speed analog and analog-to-digital interfaces, comprising an input (1) and an output (2) of a device between which a first resistor (3) is connected, an input voltage source (4) connected by alternating current between a common bus (5 ) and the input of the device (1), the second resistor (6) connected by alternating current between the output of the device (2) and the common bus (5), the equivalent load capacity (7), included by alternating current between the output of the device (2) and the common bus (5), characterized in that the output of the device (2) is connected along TERM current to the input of non-inverting voltage follower (8) and the current output (9) non-inverting current follower (10), wherein between the output of non-inverting voltage follower (8) and the noninverting input of the current mirror (10) included bipole correction circuit (11). 2. A broadband attenuator for high-speed analog and analog-to-digital interfaces according to claim 1, characterized in that the two-terminal correction circuit is made in the form of a capacitor (12), the capacitance of which is functionally connected with the equivalent load capacitance (7).

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