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參數(shù)資料
| 型號： | TUA6026K |
| 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(shù)： | 2/30頁 |
| 文件大小： | 381K |
| 代理商： | TUA6026K |
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TUA 6026
Semiconductor Group
10
1998-09-01
2
Circuit Description
2.1
Mixer-Oscillator Block
The mixer oscillator section includes two balanced mixers (double balanced mixer), two
balanced oscillators for VHF low 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 amplifier, a
double-tuned bandpass filter 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 filtered out at the balanced high-impedance output pair by means
of a parallel tuned circuit. The following SAW preamplifier has a low output impedance
to drive a 75
load directly.
2.2
PLL Block
The mixer-oscillator signal VCO/VCO 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
f
ref = 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 filter integrates the current pulses to generate
the tuning voltage for the VCO (internal amplifier, external pullup resistor at TUNE and
external RC circuitry). The charge pump output is also switched into the high-impedance
state when the control bit T0 = 1. Here it should be noted, however, 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 adjustments.
If the VCO is not working the PLL locks to a tuning voltage of 33 V.
By means of control bit 5I the pump current can be switched between two values by
software. This programmability 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.
相關PDF資料 |
PDF描述 |
|---|---|
| TUA6026S | 2-BAND, VIDEO TUNER, PDSO28 |
| TUA6026-K | 2-BAND, VIDEO TUNER, PDSO28 |
| TUA6026-S | 2-BAND, VIDEO TUNER, PDSO28 |
| TUA6028XS | 2-BAND, VIDEO TUNER, PDSO28 |
| TUA6028-S | 2-BAND, VIDEO TUNER, PDSO28 |
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