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參數資料
| 型號： | TUA6024-S |
| 廠商： | SIEMENS A G |
| 元件分類： | 調諧器 |
| 英文描述： | 2-BAND, VIDEO TUNER, PDSO28 |
| 封裝： | PLASTIC, TSSOP-28 |
| 文件頁數： | 2/25頁 |
| 文件大小： | 456K |
| 代理商： | TUA6024-S |
Preliminary Data Sheet
TUA6022, TUA6024
Semiconductor Group
6
22.3.99
9
Circuit Description
9.1
Mixer-Oscillator block
The mixer oscillator section includes two balanced mixers (double balanced mixer), two balanced oscillators
for VHF and / or HYPER band and UHF, a reference voltage source and a band switch.
Filters between tuner input and IC separate the TV frequency signals into two bands. The band switching in
the tuner front-end is done by using two or three port outputs. In the selected band the signal passes a tuner
input stage with MOSFET amplier, a double-tuned bandpass lter and is then fed to the balanced mixer input
of the IC which has in case of VHF / Hyperband a high-impedance input and in case of UHF a low-impedance
input. The input signal is mixed there with the signal from the activated on chip oscillator to the IF frequency
which is ltered out at the balanced high-impedance output pair by means of a parallel tuned circuit. The fol-
lowing SAW preamplier has a low output impedance to drive the SAW lter directly.
9.2
PLL block
The mixer-oscillator signal VCO/VCOx is internally DC-coupled as a differential signal at the programmable
divider inputs. The signal subsequently passes through a programmable divider with ratio N = 256 through
32767 and is then compared in a digital frequency / phase detector to a reference frequency fref = 62.5 kHz.
This frequency is derived from a unbalanced, low-impedance 4 MHz crystal oscillator (pin Q) divided by
Q = 64.
The phase detector has two outputs UP and DOWN that drive two current sources I+ and I- of a charge pump.
If the negative edge of the divided VCO signal appears prior to the negative edge of the reference signal, the
I+ current source pulses for the duration of the phase difference. In the reverse case the I- current source
pulses. If the two signals are in phase, the charge pump output (CHGPMP) goes into the high-impedance
state (PLL is locked). An active low-pass lter integrates the current pulses to generate the tuning voltage for
the VCO (internal amplier, external pullup resistor at TUNE and external RC circuitry). The charge pump out-
put is also switched into the high-impedance state when the control bit T0 = 1. Here it should be noted, how-
ever, that the tuning voltage can alter over a long period in the high-impedance state as a result of self-
discharge in the peripheral circuity. TUNE may be switched off by the control bit OS to allow external adjust-
ments.
If the VCO is not working the PLL locks to a tuning voltage of 33V.
By means of control bit 5I the pump current can be switched between two values by software. This program-
mability permits alteration of the control response of the PLL in the locked-in state. In this way different VCO
gains can be compensated, for example.
The software-switched ports P0, P1 and P2 are general-purpose open-collector outputs. The test bit
T1 = 1, switches the test signals fref (4 MHz / 64) and Cy (divided input signal) to P0 and P1 respectively. P0,
P1 are bidirectional.
The lock detector resets the lock ag FL when the width of the charge pump current pulses is greater than the
period of the crystal oscillator (i.e. 250 ns). Hence, when FL = 1, the maximum deviation of the input fre-
quency from the programmed frequency is given by
f = ± I
P (KVCO / fQ) (C1+C2) / (C1C2)
where IP is the charge pump current, KVCO the VCO gain, fQ the crystal oscillator frequency and C1, C2 the
capacitances in the loop lter (see application circuit). As the charge pump pulses at 62.5 kHz (= fref), it takes
a maximum of 16
s for FL to be reset after the loop has lost lock state.
Once FL has been reset, it is set only if the charge pump pulse width is less than 250 ns for eight consecutive
fref periods. Therefore it takes between 128 and 144 s for FL to be set after the loop regains lock.
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| TUA6024-S | 2-BAND, VIDEO TUNER, PDSO28 |
| TUA6026K | 2-BAND, VIDEO TUNER, PDSO28 |
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