Linear LT5554 数字可控增益200MHz放大方案

Linear公司的LT5554是7位 200MHz数字控制可编程增益放大器,增益控制范围16dB,它集成了50欧姆输入可变衰减器,和高线性可变跨导放大器.各种增益下的带宽为1GHz,200MHz时的OIP3为48dBm,IMD3为-88dBc,每次增益控制为0.125dB,增益设定时间为5ns,输入参考噪音(RTI)为1.4nV/√Hz,可用在差分ADC驱动器,IF取样收器,VGA IF功率放大器,50欧姆驱动器和仪表.本文介绍了LT5554的主要特性,方框图,应用电路以及单端输入和输出配置, 单端变压器测试板简化电路图, 单端测试板简化电路图以及宽带差分输出测试板简化电路图, PG6和STROBE时序测试简化电路图与评估板电路图.

The LT5554 is a 7-bit digitally controlled programmable gain (PG) amplifier with 16dB gain control range. It consists of a 50Ω input variable attenuator, followed by a high linearity variable transconductance amplifier. The coarse 4dB input attenuator step is implemented via 2-bits of digital control (PG5, PG6). The fine transconductance amplifier 0.125dB step within 3.875dB gain control range is set via 5-bits digital control (PG0 to PG4). The LT5554 gain control inputs (PGx) and the STROBE input can be directly coupled to TTL or ECL drivers. The seven parallel gain control inputs time skew can be eliminated by using the STROBE input positive transition.

The internal output resistor RO = 400Ω limits the maximum overall gain to 36dB for open outputs. The internal circuitry of open output collectors enables the LT5554 to be unconditionally stable over any loading conditions (including external SAW fi lters) and provides –80dB reverse isolation at 300MHz.

The LT5554 is internally protected during overdrive and has an on-chip power supply regulator. With 0.125dB step resolution and 5ns settling time, the LT5554 is suitable in applications where continuous gain control is required.

LT5554主要特性:

1GHz Bandwidth at all Gains
48dBm OIP3 at 200MHz, 2VP-P into 50Ω, ROUT = 100Ω
–88dBc IMD3 at 200MHz, 2VP-P into 50Ω, ROUT = 100Ω
1.4nV/√Hz Input-Referred-Noise (RTI)
20dBm Output P1dB at 70MHz, ROUT = 130Ω
2dB to 18dB Gain Range (ROUT = 50Ω)
0.125dB Gain Step Size
30ps Group Delay Variation
5ns Fast Gain Settling Time
5ns Fast Overdrive Recovery
–80dB Reverse Isolation

LT5554应用:
Differential ADC Driver
IF Sampling Receivers
VGA IF Power Amplifier
50Ω Driver
Instrumentation



图1.LT5554典型应用电路图



图2. LT5554方框图



图3.推荐的LT5554单端输入和输出配置:HD2 = –80dBc (10dBm, 140MHz)



图4.LT5554单端变压器测试板简化电路图



图5.LT5554单端测试板简化电路图



图6.LT5554宽带差分输出测试板简化电路图



图7.LT5554 PG6和STROBE时序测试简化电路图



图8.LT5554评估板电路图