RF64 datasheet(14/76 Pages) ETC2

14 / 76 page

ADVANCED COMMUNICATIONS & SENSING

Page 14 of 76

RF64

Tel: +86-755-82973805 Fax: +86-755-82973550 E-mail: sales@hoperf.com http://www.hoperf.com

÷75.

PFD

÷(R +1)

Vtu

Fcomp

3.2.3. PLL Architecture

The crystal oscillator (XO) forms the reference oscillator of an Integer-N Phase Locked Loop (PLL), whose

operation is discussed in the following section. Figure 5 shows a block schematic of the RF64 PLL. Here the crystal

reference frequency and the software controlled dividers R, P and S determine the output frequency of the PLL.

XT_M

XT_P

LF_M

LF_P

VCO_M

VCO_P

VR_VCO

Figure 5: Frequency Synthesizer Description

The VCO tank inductors are connected on an external differential input. Similarly, the loop filter is also located

externally. However, there is an internal 8pF capacitance at VCO input that should be subtracted from the desired

loop filter capacitance.

The output signal of the VCO is used as the input to the local oscillator (LO) generator stage, illustrated in Figure 6.

The VCO frequency is subdivided and used in a series of up (down) conversions for transmission (reception).

÷8

VCO Output

90°

LO1 Rx

LO2 Rx

Receiver

LOs

90°

÷8

LO1 Tx

LO2 Tx

Transmitter

LOs

90°

Figure 6: LO Generator

3.2.4. PLL Tradeoffs

With an integer-N PLL architecture, the following criterion must be met to ensure correct operation:

 The comparison frequency, Fcomp, of the Phase Frequency Detector (PFD) input must remain higher than six

times the PLL bandwidth (PLLBW) to guarantee loop stability and to reject harmonics of the comparison

frequency Fcomp. This is expressed in the inequality:

PLLBW ≤

Fcomp

 However the PLLBW has to be sufficiently high to allow adequate PLL lock times

 Because the divider ration R determines Fcomp, it should be set close to 119, leading to Fcomp

≈100 kHz

which will ensure suitable PLL stability and speed.

RF64 датащи(PDF) 14 Page - List of Unclassifed Manufacturers

RF64 датащи(HTML) 14 Page - List of Unclassifed Manufacturers

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76

датащи скачать

ссылки URL