没有合适的资源?快使用搜索试试~ 我知道了~
UAF42是美国Burr-Brown公司推出的高集成度通用有源滤波器,它具有设计方便、使用灵活的特点。通过改变UAF42的电路参数可以构成各种满足工程实际需要的滤波器。文中介绍了UAF42的引脚功能、内部结构和工作原理,并给出了由UAF42构成的双极有源滤波器及60Hz限波电路的具体电路和参数设计
资源推荐
资源详情
资源评论
1
FIGURE 1. Two-Pole Low-Pass Filter Using UAF42.
NOTE: A UAF42 and two external resistors make a unity-gain, two-pole, 1.25dB ripple
Chebyshev low-pass filter. With the resistor values shown, cutoff frequency is 10kHz.
Although active filters are vital in modern electronics, their
design and verification can be tedious and time consuming.
To aid in the design of active filters, Burr-Brown provides a
series of FilterPro™ computer-aided design programs. Us-
ing the FILTER42 program and the UAF42 it is easy to
design and implement all kinds of active filters. The UAF42
is a monolithic IC which contains the op amps, matched
resistors, and precision capacitors needed for a state-variable
filter pole-pair. A fourth, uncommitted precision op amp is
also included on the die.
Filters implemented with the UAF42 are time-continuous,
free from the switching noise and aliasing problems of
switched-capacitor filters. Other advantages of the state-
variable topology include low sensitivity of filter parameters
to external component values and simultaneous low-pass,
high-pass, and band-pass outputs. Simple two-pole filters
can be made with a UAF42 and two external resistors—see
Figure 1.
The DOS-compatible program guides you through the de-
sign process and automatically calculates component values.
Low-pass, high-pass, band-pass, and band-reject (or notch)
filters can be designed.
Active filters are designed to approximate an ideal filter
response. For example, an ideal low-pass filter completely
eliminates signals above the cutoff frequency (in the stop-
band), and perfectly passes signals below it (in the pass-
band). In real filters, various trade-offs are made in an
attempt to approximate the ideal. Some filter types are
optimized for gain flatness in the pass-band, some trade-off
gain variation or ripple in the pass-band for a steeper rate of
attenuation between the pass-band and stop-band (in the
transition-band), still others trade-off both flatness and rate
of roll-off in favor of pulse-response fidelity. FILTER42
supports the three most commonly used all-pole filter types:
Butterworth, Chebyshev, and Bessel. The less familiar In-
verse Chebyshev is also supported. If a two-pole band-pass
or notch filter is selected, the program defaults to a resonant-
circuit response.
Butterworth (maximally flat magnitude). This filter has the
flattest possible pass-band magnitude response. Attenuation
is –3dB at the design cutoff frequency. Attenuation beyond
the cutoff frequency is a moderately steep –20dB/decade/
pole. The pulse response of the Butterworth filter has mod-
erate overshoot and ringing.
Chebyshev (equal ripple magnitude). (Other transliterations
of the Russian Heby]ov are Tschebychev, Tschebyscheff
or Tchevysheff). This filter response has steeper initial rate
of attenuation beyond the cutoff frequency than Butterworth.
A
1
R
2
50kΩ
A
2
A
3
R
4
50kΩ
UAF42
11
R
1
50kΩ
R
F1
15.8kΩ
R
F2
15.8kΩ
C
1
1000pF
C
2
1000pF
13 8 7 14
2
V
IN
R
3
50kΩ
V
O
1
FILTER DESIGN PROGRAM FOR
THE UAF42 UNIVERSAL ACTIVE FILTER
By Johnnie Molina and R. Mark Stitt (602) 746-7592
APPLICATION BULLETIN
®
Mailing Address: PO Box 11400 • Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd. • Tucson, AZ 85706
Tel: (602) 746-1111 • Twx: 910-952-111 • Telex: 066-6491 • FAX (602) 889-1510 • Immediate Product Info: (800) 548-6132
©
1991 Burr-Brown Corporation AB-035C Printed in U.S.A. July, 1993
SBFA002
2
This advantage comes at the penalty of amplitude variation
(ripple) in the pass-band. Unlike Butterworth and Bessel
responses, which have 3dB attenuation at the cutoff fre-
quency, Chebyshev cutoff frequency is defined as the fre-
quency at which the response falls below the ripple band.
For even-order filters, all ripple is above the dc-normalized
passband gain response, so cutoff is at 0dB (see Figure 2A).
For odd-order filters, all ripple is below the dc-normalized
passband gain response, so cutoff is at –(ripple) dB (see
Figure 2B). For a given number of poles, a steeper cutoff can
be achieved by allowing more pass-band ripple. The
Chebyshev has more ringing in its pulse response than the
Butterworth—especially for high-ripple designs.
Inverse Chebyshev (equal minima of attenuation in the stop
band). As its name implies, this filter type is cousin to the
Chebyshev. The difference is that the ripple of the Inverse
Chebyshev filter is confined to the stop-band. This filter type
has a steep rate of roll-off and a flat magnitude response in
the pass-band. Cutoff of the Inverse Chebyshev is defined as
the frequency where the response first enters the specified
stop-band—see Figure 3. Step response of the Inverse
Chebyshev is similar to the Butterworth.
Bessel (maximally flat time delay), also called Thomson.
Due to its linear phase response, this filter has excellent
pulse response (minimal overshoot and ringing). For a given
number of poles, its magnitude response is not as flat, nor is
its initial rate of attenuation beyond the –3dB cutoff fre-
quency as steep as the Butterworth. It takes a higher-order
Bessel filter to give a magnitude response similar to a given
Butterworth filter, but the pulse response fidelity of the
Bessel filter may make the added complexity worthwhile.
Tuned Circuit (resonant or tuned-circuit response). If a
two-pole band-pass or band-reject (notch) filter is selected,
the program defaults to a tuned circuit response. When band-
pass response is selected, the filter design approximates the
response of a series-connected LC circuit as shown in Figure
4A. When a two-pole band-reject (notch) response is se-
lected, filter design approximates the response of a parallel-
connected LC circuit as shown in Figure 4B.
CIRCUIT IMPLEMENTATION
In general, filters designed by this program are implemented
with cascaded filter subcircuits. Subcircuits either have a
two-pole (complex pole-pair) response or a single real-pole
response. The program automatically selects the subcircuits
required based on function and performance. A program
option allows you to override the automatic topology selec-
tion routine to specify either an inverting or noninverting
pole-pair configuration.
FIGURE 3. Response vs Frequency for 5-pole, –60dB
Stop-Band, Inverse Chebyshev Low-Pass Filter
Showing Cutoff at –60dB.
FILTER RESPONSE vs FREQUENCY
Normalized Frequency
f /100
C
f /10
C
f
C
10f
C
+10
0
–10
–20
–30
–40
–50
Filter Response (dB)
5-Pole Chebyshev
3dB Ripple
Ripple
FILTER RESPONSE vs FREQUENCY
Normalized Frequency
f /100
C
f /10
C
f
C
10f
C
+10
0
–10
–20
–30
–40
–50
Filter Response (dB)
4-Pole Chebyshev
3dB Ripple
Ripple
FIGURE 2A. Response vs Frequency for Even-Order (4-
pole) 3dB Ripple Chebyshev Low-Pass Filter
Showing Cutoff at 0dB.
FIGURE 2B. Response vs Frequency for Odd-Order (5-
pole) 3dB Ripple Chebyshev Low-Pass Filter
Showing Cutoff at –3dB.
FILTER RESPONSE vs FREQUENCY
f
C
/10
Normalized Frequency
f
C
10f
C
100f
C
Normalized Gain (dB)
20
0
–20
–40
–60
–80
–100
A
MIN
f
STOPBAND
3
FIGURE 6. Multiple-Stage Filter Made with Two or More
Subcircuits.
NOTES:
(1) Subcircuit will be a real-pole high-pass (HP), real-pole low-pass
(LP), or complex pole-pair (PP1 through PP6) subcircuit specified
on the
UAF42 Filter Component Values
and
Filter Block Diagram
program outputs.
(2) If the subcircuit is a pole-pair section, HP Out, BP Out, LP Out, or
Aux Out will be specified on the UAF42
Filter Block Diagram
program output.
V
IN
V
O
Subcircuit N
In Out
(2)
(1)
Subcircuit 1
In Out
(2)
(1)
NOTES:
(1) Subcircuit will be a complex pole-pair (PP1 through PP6)
subcircuit specified on the
UAF42 Filter Component Values
and
Filter Block Diagram
program outputs.
(2) HP Out, BP Out, LP Out, or Aux Out will be specified on the
UAF42
Filter Block Diagram
program output.
V
IN
V
O
Subcircuit 1
In Out
(2)
(1)
FIGURE 5. Simple Filter Made with Single Complex Pole-
Pair Subcircuit.
FIGURE 4B. n = 2 Band-Reject (Notch) Filter Using
UAF42 (approximates the response of a par-
allel-connected tuned L, C, R circuit).
FIGURE 4A. n = 2 Band-Pass Filter Using UAF42 (ap-
proximates the response of a series-connected
tuned L, C, R circuit).
The simplest filter circuit consists of a single pole-pair
subcircuit as shown in Figure 5. More complex filters
consist of two or more cascaded subcircuits as shown in
Figure 6. Even-order filters are implemented entirely with
UAF42 pole-pair sections and normally require no external
capacitors. Odd-order filters additionally require one real
pole section which can be implemented with the fourth
uncommitted op amp in the UAF42, an external resistor, and
an external capacitor. The program can be used to design
filters up to tenth order.
The program guides you through the filter design and gen-
erates component values and a block diagram describing the
filter circuit. The Filter Block Diagram program output
shows the subcircuits needed to implement the filter design
labeled by type and connected in the recommended order.
The Filter Component Values program output shows the
values of all external components needed to implement the
filter.
C
L
V
IN
V
O
R
C
L
V
IN
V
O
R
SUMMARY OF FILTER TYPES
Butterworth
Advantages: Maximally flat magnitude
response in the pass-band.
Good all-around performance.
Pulse response better than
Chebyshev.
Rate of attenuation better than
Bessel.
Disadvantages: Some overshoot and ringing in
step response.
Chebyshev
Advantages: Better rate of attenuation
beyond the pass-band than
Butterworth.
Disadvantages: Ripple in pass-band.
Considerably more ringing in
step response than Butterworth.
Inverse Chebyshev
Advantages: Flat magnitude response in
pass-band with steep rate of
attenuation in transition-band.
Disadvantages: Ripple in stop-band.
Some overshoot and ringing in
step response.
Bessel
Advantages: Best step response—very little
overshoot or ringing.
Disadvantages: Slower initial rate of attenua-
tion beyond the pass-band than
Butterworth.
剩余14页未读,继续阅读
资源评论
tj0803741177
- 粉丝: 7
- 资源: 17
上传资源 快速赚钱
- 我的内容管理 展开
- 我的资源 快来上传第一个资源
- 我的收益 登录查看自己的收益
- 我的积分 登录查看自己的积分
- 我的C币 登录后查看C币余额
- 我的收藏
- 我的下载
- 下载帮助
安全验证
文档复制为VIP权益,开通VIP直接复制
信息提交成功