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参数资料
| 型号： | ACVTX1018A-FREQ-C20-H5-OUT23 |
| 厂商： | ABRACON CORP |
| 元件分类： | XO, clock |
| 英文描述： | TCVCXO, CLOCK, 1 MHz - 26 MHz, CMOS/TTL OUTPUT |
| 封装： | COMPACT, DIP-4 |
| 文件页数： | 5/6页 |
| 文件大小： | 177K |
| 代理商： | ACVTX1018A-FREQ-C20-H5-OUT23 |
29 Journey Aliso Viejo, CA 92656 USA
(949) 448-7070
FAX: (949) 448-8484
E-MAIL:
abinfo @ abracon.com INTERNET ADDRESS: www.abracon.com
ABRACON IS
ISO 9001 / QS 9000
CERTIFIED
CORPORA TION
ABRACON
-59 -
VCXOs and TCXOs
QUESTIONS AND ANSWERS
Q: What are the factors that affect frequency pullability?
A: The frequency pullability or deviation in VCXO is the change in
the output frequency with respect to
change in control voltage.
Pullability is usually specified as min-
imum; however, in some applications,
a maximum pulling value is also
specified to avoid circuit instability.
Please refer to figure 1 for a typical
Colpitts VCXO circuit:
Some major factors that affect the frequency deviation in VCXO:
Load capacitance value C1 and C2.
Frequency.
Crystal characteristics (C1, C0/C1, size)
Varactor type and capacitance.
Voltage control Vc.
Operating temperature.
The frequency pullability can be increased either by using a
low capacitance with sharp slope varactor, connect in series
another varactor or an inductor, adjusting load capacitor val-
ues C1 and C2, or increasing control voltage.
Be very careful when considering any above methods because
it may create circuit instability which has a severe effect on jit-
ter, linearity, unwanted modes, frequency hysteresis, or fre-
quency shift over temperature.
Q: What is the typical input impedance?
The input impedance is a function of modulation frequency. Its
minimum input impedance is 50kW at 10kHz.
Q: What is the transfer function?
A: The transfer function is the direction of change in frequency
versus the change in control voltage. Most applications
require a positive transfer function, which the frequency rises
when increasing control voltage.
Q: What is linearity and what are the factors that affect it?
A: Linearity is the deviation
from the best straight-
line slope of the
frequency versus control
voltage curve. The typi-
cal linearity in Abracon
VCXO is ±10% maxi-
mum for standard pulla-
bility. Larger pulling may
worsen the linearity.
Q: What is the modulation bandwidth?
A: The modulation bandwidth is the minimum ±3dB bandwidth
frequency, relative to a 1kHz to 10kHz modulation frequency.
Unless otherwise specified as default, other values of modula-
tion bandwidth and frequency must be specified when ordering.
Q: What is the control voltage?
A: The control voltage is the external voltage applied to the input
of the VCXO. It consists of a minimum, a maximum, and a
center voltage. The center control voltage is the nominal volt-
age that sets the oscillation frequency to its minimal value.
Standard control voltages:
Vc min = 0.5Vdc; Vc max. = 4.5Vdc; Vc center = 2.5Vdc ± 0.5V
Q: What is a TCXO?
A: A TCXO (Temperature-Compensated Crystal Oscillator) is a
crystal oscillator that has a high-precision crystal, a tempera-
ture-compensated network. There are several methods to
design a compensated network, which could vary from simple,
less expensive to, complicate and very expensive:
Method 1: Thermistor/Capacitor networks
(Direct compensation). Lowest cost, no varactor needed.
Method 2: Traditional thermistor network.
Method 3: Analog Polynomial Generator
Method 4: Digitally segmented analog
Method 5: Digital compensation
Method 6: Digital compensation with DAC voltage summers.
Figure 3
shows a
traditional
thermistor
network:
Q: Why and when we need to use a TCXO?
A: We need to use a TCXO when the frequency stability of the
oscillator falls beyond the design limitation of a standard simple
(fixed) crystal oscillator which is typically less than ±5ppm over a
standard or extended temperature window. The TCXO costs
more due to its complex circuit and manufacturing.
Q: Why there is an internal trimmer or control voltage on a
TCXO?
A: The purpose of the internal trimmer (variable capacitor) or a
control voltage is to re-adjust the frequency to its nominal fre-
quency for aging compensation or initial setting.
The internal trimmer is accessible via a hole on top of the
TCXO can and can be adjusted with a special tool.
The control voltage can be set with a voltage divider or an
external voltage. Both methods of adjustment usually can not
produce large frequency deviation rather than 5 to 15ppm
enough to offset the frequency due to standard aging.
Q: How to specify frequency stability on a TCXO?
A: Unless otherwise specified, the frequency stability on a TCXO
is specified as follows:
Due to temperature change: ± 2.5ppm @ -20°C to +70°C
Due to aging: ± 1ppm per year max.
Due to supply voltage (±5%): ± 0.3ppm max.
The frequency drift due to temperature change is referred to nom-
inal frequency set at 25°C.
Figure 1
Figure 3
Figure 2
22355 Abracon CORX 2-29.qxd
3/6/00
6:55 AM
Page 59
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相关代理商/技术参数 |
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|---|---|
| ACVTX1018S | 制造商:ABRACON 制造商全称:Abracon Corporation 功能描述:5Vdc or 3.3Vdc TTL / CMOSAND SINE WAVE TEMPERATURE-COMPENSATED XTAL OSCILLATORS |
| ACVX1220 | 制造商:ABRACON 制造商全称:Abracon Corporation 功能描述:TTL/CMOS FULL-SIZE DIP VOLTAGE CONTROLLED CRYSTAL OSCILLATOR |
| ACVX1220_07 | 制造商:ABRACON 制造商全称:Abracon Corporation 功能描述:TTL/CMOS FULL-SIZE DIP VOLTAGE CONTROLLED CRYSTAL OSCILLATOR |
| ACVX1220L | 制造商:ABRACON 制造商全称:Abracon Corporation 功能描述:TTL/CMOS 3.3Vdc VOLTAGE CONTROLLED CRYSTAL OSCILLATOR |
| ACVX1220L-27.000-E-R-S-N20-Q15 | 制造商:Abracon Corporation 功能描述:ACVX1220L Series 120 MHz 20.8 x 12.6 mm 3.3 V 25 ppm Crystal Oscillator |
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