Output Limiting. HS-1135RH Datasheet
August 1999 File Number 4099.2
Radiation Hardened, High Speed, Low
Power Current Feedback Ampliﬁer with
Programmable Output Limiting
The HS-1135RH is a radiation hardened, high speed, low
power current feedback ampliﬁer built with Intersil’s
proprietary complementary bipolar UHF-1 (DI bonded wafer)
process. They are QML approved and processed in full
compliance with MIL-PRF-38535. This ampliﬁer features
user programmable output limiting, via the VH and VL pins.
The HS-1135RH is the ideal choice for high speed, low
power applications requiring output limiting (e.g., ﬂash A/D
drivers), especially those requiring fast overdrive recovery
times. The limiting function allows the designer to set the
maximum and minimum output levels to protect downstream
stages from damage or input saturation. The sub-
nanosecond overdrive recovery time ensures a quick return
to linear operation following an overdrive condition.
Component and composite video systems also beneﬁt from
this op amp’s performance, as indicated by the gain ﬂatness,
and differential gain and phase speciﬁcations.
Speciﬁcations for Rad Hard QML devices are controlled
by the Defense Supply Center in Columbus (DSCC). The
SMD numbers listed here must be used when ordering.
Detailed Electrical Speciﬁcations for these devices are
contained in SMD 5962-96767. A “hot-link” is provided
on our homepage for downloading.
-55 to 125
-55 to 125
HS7-1135RH/PROTO HS7-1135RH/PROTO -55 to 125
• Electrically Screened to SMD # 5962-96767
• QML Qualiﬁed per MIL-PRF-38535 Requirements
• User Programmable Output Voltage Limiting
• Fast Overdrive Recovery . . . . . . . . . . . . . . . . . <1ns (Typ)
• Low Supply Current . . . . . . . . . . . . . . . . . . . . 6.9mA (Typ)
• Wide -3dB Bandwidth. . . . . . . . . . . . . . . . . .360MHz (Typ)
• High Slew Rate. . . . . . . . . . . . . . . . . . . . . .1200V/µs (Typ)
• High Input Impedance . . . . . . . . . . . . . . . . . . . 2MΩ (Typ)
• Excellent Gain Flatness (to 50MHz). . . . . . ±0.07dB (Typ)
• Total Gamma Dose. . . . . . . . . . . . . . . . . . . . 300kRAD(Si)
• Latch Up . . . . . . . . . . . . . . . . . . . . . None (DI Technology)
• Flash A/D Driver
• Video Switching and Routing
• Pulse and Video Ampliﬁers
• Wideband Ampliﬁers
• RF/IF Signal Processing
• Imaging Systems
OR CDIP2-TI (SBDIP)
1 CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 321-724-7143 | Copyright © Intersil Corporation 1999
The HS-1135RH features user programmable output clamps
to limit output voltage excursions. Clamping action is obtained
by applying voltages to the VH and VL terminals (pins 8 and 5)
of the amplifier. VH sets the upper output limit, while VL sets
the lower clamp level. If the amplifier tries to drive the output
above VH, or below VL, the clamp circuitry limits the output
voltage at VH or VL ( the clamp accuracy), respectively. The
low input bias currents of the clamp pins allow them to be
driven by simple resistive divider circuits, or active elements
such as amplifiers or DACs.
Figure 1 shows a simpliﬁed schematic of the HS-1135RH
input stage, and the high clamp (VH) circuitry. As with all
current feedback ampliﬁers, there is a unity gain buffer (QX1
- QX2) between the positive and negative inputs. This buffer
forces -IN to track +IN, and sets up a slewing current of (V-
IN - VOUT)/RF. This current is mirrored onto the high
impedance node (Z) by QX3-QX4, where it is converted to a
voltage and fed to the output via another unity gain buffer. If
no clamping is utilized, the high impedance node may swing
within the limits deﬁned by QP4 and QN4. Note that when the
output reaches it’s quiescent value, the current ﬂowing
through -IN is reduced to only that small current (-IBIAS)
required to keep the output at the ﬁnal voltage.
FIGURE 1. HS-1135RH SIMPLIFIED VH CLAMP CIRCUITRY
Tracing the path from VH to Z illustrates the effect of the
clamp voltage on the high impedance node. VH decreases
by 2VBE (QN6 and QP6) to set up the base voltage on QP5.
QP5 begins to conduct whenever the high impedance node
reaches a voltage equal to QP5’s base + 2VBE (QP5 and
QN5). Thus, QP5 clamps node Z whenever Z reaches VH.
R1 provides a pull-up network to ensure functionality with
the clamp inputs ﬂoating. A similar description applies to the
symmetrical low clamp circuitry controlled by VL.
When the output is clamped, the negative input continues to
source a slewing current (ICLAMP) in an attempt to force the
output to the quiescent voltage defined by the input. QP5 must
sink this current while clamping, because the -IN current is
always mirrored onto the high impedance node. The clamping
current is calculated as (V-IN - VOUT)/RF. As an example, a
unity gain circuit with VIN = 2V, VH = 1V, and RF = 510Ω would
have ICLAMP = (2-1)/510Ω = 1.96mA. Note that ICC will
increase by ICLAMP when the output is clamp limited.
The clamped output voltage will not be exactly equal to the
voltage applied to VH or VL. Offset errors, mostly due to VBE
mismatches, necessitate a clamp accuracy parameter which is
found in the device specifications. Clamp accuracy is a function
of the clamping conditions. Referring again to Figure 1, it can
be seen that one component of clamp accuracy is the VBE
mismatch between the QX6 transistors, and the QX5 transistors.
If the transistors always ran at the same current level there
would be no VBE mismatch, and no contribution to the
inaccuracy. The QX6 transistors are biased at a constant
current, but as described earlier, the current through QX5 is
equivalent to ICLAMP. VBE increases as ICLAMP increases,
causing the clamped output voltage to increase as well. ICLAMP
is a function of the overdrive level (V-IN -VOUTCLAMPED) and
RF, so clamp accuracy degrades as the overdrive increases, or
as RF decreases. As an example, the specified accuracy of
±60mV for a 2X overdrive with RF = 510Ω degrades to ±220mV
for RF = 240Ω at the same overdrive, or to ±250mV for a 3X
overdrive with RF = 510Ω.
Consideration must also be given to the fact that the clamp
voltages have an effect on ampliﬁer linearity. The
“Nonlinearity Near Clamp Voltage” curve in the data sheet
illustrates the impact of several clamp levels on linearity.
Unlike some competitor devices, both VH and VL have usable
ranges that cross 0V. While VH must be more positive than VL,
both may be positive or negative, within the range restrictions
indicated in the specifications. For example, the HS-1135RH
could be limited to ECL output levels by setting VH = -0.8V and
VL = -1.8V. VH and VL may be connected to the same voltage
(GND for instance) but the result won’t be in a DC output
voltage from an AC input signal. A 150 - 200mV AC signal will
still be present at the output.
Recovery from Overdrive
The output voltage remains at the clamp level as long as the
overdrive condition remains. When the input voltage drops
below the overdrive level (VCLAMP/AVCL) the ampliﬁer will
return to linear operation. A time delay, known as the
Overdrive Recovery Time, is required for this resumption of
linear operation. The plots of “Unclamped Performance” and
“Clamped Performance” highlight the HS-1135RH’s